Gave the word biology

Last Update: Jan 03, 2023

This is a question our experts keep getting from time to time. Now, we have got the complete detailed explanation and answer for everyone, who is interested!

Asked by: Dr. Gussie Kihn DVM

Score: 4.3/5
(57 votes)

The word biology is derived from the greek words /bios/ meaning /life/ and /logos/ meaning /study/ and is defined as the science of life and living organisms. An organism is a living entity consisting of one cell e.g. bacteria, or several cells e.g. animals, plants and fungi.

Who gave biology word?

The term biology in its modern sense appears to have been introduced independently by Thomas Beddoes (in 1799), Karl Friedrich Burdach (in 1800), Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and Jean-Baptiste Lamarck (Hydrogéologie, 1802).

Who is the father of biology?

Therefore, Aristotle is called the Father of biology. He was a great Greek philosopher and polymath. His theory of biology also known as the “Aristotle’s biology” describes five major biological processes, namely, metabolism, temperature regulation, inheritance, information processing and embryogenesis.

Who first invented biology?

The science of biology was invented by Aristotle (384–322 BC).

What are the 8 characters of life?

All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, growth and development, regulation, homeostasis, and energy processing. When viewed together, these eight characteristics serve to define life.

25 related questions found

From Simple English Wikipedia, the free encyclopedia

Biology is the science that studies life, living things, and the evolution of life. Living things include animals, plants, fungi (such as mushrooms), and microorganisms such as bacteria and archaea.

The term ‘biology’ is relatively modern. It was introduced in 1799 by a physician, Thomas Beddoes.^[1]

People who study biology are called biologists. Biology looks at how animals and other living things behave and work, and what they are like. Biology also studies how organisms react with each other and the environment. It has existed as a science for about 200 years, and before that it was called «natural history». Biology has many research fields and branches. Like all sciences, biology uses the scientific method. This means that biologists must be able to show evidence for their ideas and that other biologists must be able to test the ideas for themselves.

Biology attempts to answer questions such as:

• «What are the characteristics of this living thing?» (comparative anatomy)
• «How do the parts work?» (physiology)
• «How should we group living things?» (classification, taxonomy)
• «What does this living thing do?» (behaviour, growth)
• «How does inheritance work?» (genetics)
• «What is the history of life?» (palaeontology)
• «How do living things relate to their environment?» (ecology)

Modern biology is influenced by evolution, which answers the question: «How has the living world come to be as it is?»

History[change | change source]

The word biology comes from the Greek word βίος (bios), «life», and the suffix -λογία (logia), «study of».^[2][3]

Branches[change | change source]

• Algalogy
• Anatomy
• Arachnology
• Bacteriology
• Biochemistry
• Biogeography
• Biophysics
• Botany
• Bryology
• Cell biology
• Cytology
• Dendrology
• Developmental biology
• Ecology
• Endocrinology
• Entomology
• Embryology
• Ethology
• Evolution / Evolutionary biology
• Genetics / Genomics
• Herpetology
• Histology
• Human biology / Anthropology / Primatology
• Ichthyology
• Limnology
• Mammalology
• Marine biology
• Microbiology / Bacteriology
• Molecular biology
• Morphology
• Mycology / Lichenology
• Ornithology
• Palaeontology
• Parasitology
• Phycology
• Phylogenetics
• Physiology
• Taxonomy
• Virology
• Zoology

References[change | change source]

Biology is the scientific study of life.^[1][2][3] It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field.^[1][2][3] For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life.^[1][2][3] Energy processing is also important to life as it allows organisms to move, grow, and reproduce.^[1][2][3] Finally, all organisms are able to regulate their own internal environments.^{[1][2][3][4][5]}

Biologists are able to study life at multiple levels of organization,^[1] from the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations.^[1][6] Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use.^[7][8][9] Like other scientists, biologists use the scientific method to make observations, pose questions, generate hypotheses, perform experiments, and form conclusions about the world around them.^[1]

Life on Earth, which emerged more than 3.7 billion years ago,^[10] is immensely diverse. Biologists have sought to study and classify the various forms of life, from prokaryotic organisms such as archaea and bacteria to eukaryotic organisms such as protists, fungi, plants, and animals. These various organisms contribute to the biodiversity of an ecosystem, where they play specialized roles in the cycling of nutrients and energy through their biophysical environment.

History

The earliest of roots of science, which included medicine, can be traced to ancient Egypt and Mesopotamia in around 3000 to 1200 BCE.^[11][12] Their contributions shaped ancient Greek natural philosophy.^{[11][12][13][14]} Ancient Greek philosophers such as Aristotle (384–322 BCE) contributed extensively to the development of biological knowledge. He explored biological causation and the diversity of life. His successor, Theophrastus, began the scientific study of plants.^[15] Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dīnawarī (828–896), who wrote on botany,^[16] and Rhazes (865–925) who wrote on anatomy and physiology. Medicine was especially well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew heavily on Aristotelian thought.

Biology began to quickly develop with Anton van Leeuwenhoek’s dramatic improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop techniques of microscopic dissection and staining.^[17] Advances in microscopy had a profound impact on biological thinking. In the early 19th century, biologists pointed to the central importance of the cell. In 1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, although they opposed the idea that (3) all cells come from the division of other cells, continuing to support spontaneous generation. However, Robert Remak and Rudolf Virchow were able to reify the third tenet, and by the 1860s most biologists accepted all three tenets which consolidated into cell theory.^[18][19]

Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735, and in the 1750s introduced scientific names for all his species.^[20] Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent.^[21]

Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who presented a coherent theory of evolution.^[23] The British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Malthus’s writings on population growth, and his own morphological expertise and extensive natural observations, forged a more successful evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel Wallace to independently reach the same conclusions.^[24][25]

The basis for modern genetics began with the work of Gregor Mendel in 1865.^[26] This outlined the principles of biological inheritance.^[27] However, the significance of his work was not realized until the early 20th century when evolution became a unified theory as the modern synthesis reconciled Darwinian evolution with classical genetics.^[28] In the 1940s and early 1950s, a series of experiments by Alfred Hershey and Martha Chase pointed to DNA as the component of chromosomes that held the trait-carrying units that had become known as genes. A focus on new kinds of model organisms such as viruses and bacteria, along with the discovery of the double-helical structure of DNA by James Watson and Francis Crick in 1953, marked the transition to the era of molecular genetics. From the 1950s onwards, biology has been vastly extended in the molecular domain. The genetic code was cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain codons. The Human Genome Project was launched in 1990 to map the human genome.^[29]

Chemical basis

Atoms and molecules

All organisms are made up of chemical elements;^[30] oxygen, carbon, hydrogen, and nitrogen account for most (96%) of the mass of all organisms, with calcium, phosphorus, sulfur, sodium, chlorine, and magnesium constituting essentially all the remainder. Different elements can combine to form compounds such as water, which is fundamental to life.^[30] Biochemistry is the study of chemical processes within and relating to living organisms. Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms, and interactions.

Water

Life arose from the Earth’s first ocean, which formed some 3.8 billion years ago.^[31] Since then, water continues to be the most abundant molecule in every organism. Water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. Once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life.^[31] In terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen (H) atoms to one oxygen (O) atom (H₂O).^[31] Because the O–H bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge.^[31] This polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive.^[31] Surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid.^[31] Water is also adhesive as it is able to adhere to the surface of any polar or charged non-water molecules.^[31] Water is denser as a liquid than it is as a solid (or ice).^[31] This unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above.^[31] Water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol.^[31] Thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor.^[31] As a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again.^[31] In pure water, the number of hydrogen ions balances (or equals) the number of hydroxyl ions, resulting in a pH that is neutral.

Organic compounds

Organic compounds are molecules that contain carbon bonded to another element such as hydrogen.^[31] With the exception of water, nearly all the molecules that make up each organism contain carbon.^[31][32] Carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules.^[31][32] For example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide (CO₂), or a triple covalent bond such as in carbon monoxide (CO). Moreover, carbon can form very long chains of interconnecting carbon–carbon bonds such as octane or ring-like structures such as glucose.

The simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other elements such as oxygen (O), hydrogen (H), phosphorus (P), and sulfur (S), which can change the chemical behavior of that compound.^[31] Groups of atoms that contain these elements (O-, H-, P-, and S-) and are bonded to a central carbon atom or skeleton are called functional groups.^[31] There are six prominent functional groups that can be found in organisms: amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group.^[31]

In 1953, the Miller-Urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early Earth, thus suggesting that complex organic molecules could have arisen spontaneously in early Earth (see abiogenesis).^[33][31]

Macromolecules

Macromolecules are large molecules made up of smaller subunits or monomers.^[34] Monomers include sugars, amino acids, and nucleotides.^[35] Carbohydrates include monomers and polymers of sugars.^[36]
Lipids are the only class of macromolecules that are not made up of polymers. They include steroids, phospholipids, and fats,^[35] largely nonpolar and hydrophobic (water-repelling) substances.^[37]
Proteins are the most diverse of the macromolecules. They include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. The basic unit (or monomer) of a protein is an amino acid.^[34] Twenty amino acids are used in proteins.^[34]
Nucleic acids are polymers of nucleotides.^[38] Their function is to store, transmit, and express hereditary information.^[35]

Cells

Cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division.^[39] Most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope.^[40] There are generally two types of cells: eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. Prokaryotes are single-celled organisms such as bacteria, whereas eukaryotes can be single-celled or multicellular. In multicellular organisms, every cell in the organism’s body is derived ultimately from a single cell in a fertilized egg.

Cell structure

Every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space.^[41] A cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. Cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions.^[42] Cell membranes also contains membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell.^[43] Cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton.

Within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids.^[44] In addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units.^[45] These organelles include the cell nucleus, which contains most of the cell’s DNA, or mitochondria, which generates adenosine triphosphate (ATP) to power cellular processes. Other organelles such as endoplasmic reticulum and Golgi apparatus play a role in the synthesis and packaging of proteins, respectively. Biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. Plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds.^[45] Eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles.^[45] In terms of their structural composition, the microtubules are made up of tubulin (e.g., α-tubulin and β-tubulin whereas intermediate filaments are made up of fibrous proteins.^[45] Microfilaments are made up of actin molecules that interact with other strands of proteins.^[45]

Metabolism

All cells require energy to sustain cellular processes. Metabolism is the set of chemical reactions in an organism. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conversion of food/fuel to monomer building blocks; and the elimination of metabolic wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolic reactions may be categorized as catabolic—the breaking down of compounds (for example, the breaking down of glucose to pyruvate by cellular respiration); or anabolic—the building up (synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy, and anabolism consumes energy. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts—they allow a reaction to proceed more rapidly without being consumed by it—by reducing the amount of activation energy needed to convert reactants into products. Enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell’s environment or to signals from other cells.

Cellular respiration

Cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.^[46] The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. Respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. The overall reaction occurs in a series of biochemical steps, some of which are redox reactions. Although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions.

Sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. Cellular respiration involving oxygen is called aerobic respiration, which has four stages: glycolysis, citric acid cycle (or Krebs cycle), electron transport chain, and oxidative phosphorylation.^[47] Glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of ATP being produced at the same time.^[47] Each pyruvate is then oxidized into acetyl-CoA by the pyruvate dehydrogenase complex, which also generates NADH and carbon dioxide. Acetyl-Coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. At the end of the cycle, the total yield from 1 glucose (or 2 pyruvates) is 6 NADH, 2 FADH₂, and 2 ATP molecules. Finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. Oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from NADH and FADH₂ that is coupled to the pumping of protons (hydrogen ions) across the inner mitochondrial membrane (chemiosmosis), which generates a proton motive force.^[47] Energy from the proton motive force drives the enzyme ATP synthase to synthesize more ATPs by phosphorylating ADPs. The transfer of electrons terminates with molecular oxygen being the final electron acceptor.

If oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD⁺ so it can be re-used in glycolysis. In the absence of oxygen, fermentation prevents the buildup of NADH in the cytoplasm and provides NAD⁺ for glycolysis. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by NADH. During anaerobic glycolysis, NAD⁺ regenerates when pairs of hydrogen combine with pyruvate to form lactate. Lactate formation is catalyzed by lactate dehydrogenase in a reversible reaction. Lactate can also be used as an indirect precursor for liver glycogen. During recovery, when oxygen becomes available, NAD⁺ attaches to hydrogen from lactate to form ATP. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate-level phosphorylation, which does not require oxygen.

Photosynthesis

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism’s metabolic activities via cellular respiration. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water.^[48][49][50] In most cases, oxygen is released as a waste product. Most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the Earth’s atmosphere, and supplies most of the energy necessary for life on Earth.^[51]

Photosynthesis has four stages: Light absorption, electron transport, ATP synthesis, and carbon fixation.^[47] Light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. The absorbed light energy is used to remove electrons from a donor (water) to a primary electron acceptor, a quinone designated as Q. In the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a final electron acceptor, which is usually the oxidized form of NADP⁺, which is reduced to NADPH, a process that takes place in a protein complex called photosystem I (PSI). The transport of electrons is coupled to the movement of protons (or hydrogen) from the stroma to the thylakoid membrane, which forms a pH gradient across the membrane as hydrogen becomes more concentrated in the lumen than in the stroma. This is analogous to the proton-motive force generated across the inner mitochondrial membrane in aerobic respiration.^[47]

During the third stage of photosynthesis, the movement of protons down their concentration gradients from the thylakoid lumen to the stroma through the ATP synthase is coupled to the synthesis of ATP by that same ATP synthase.^[47] The NADPH and ATPs generated by the light-dependent reactions in the second and third stages, respectively, provide the energy and electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate (RuBP) in a sequence of light-independent (or dark) reactions called the Calvin cycle.^[52]

Cell signaling

Cell signaling (or communication) is the ability of cells to receive, process, and transmit signals with its environment and with itself.^[53][54] Signals can be non-chemical such as light, electrical impulses, and heat, or chemical signals (or ligands) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell.^[55][54] There are generally four types of chemical signals: autocrine, paracrine, juxtacrine, and hormones.^[55] In autocrine signaling, the ligand affects the same cell that releases it. Tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self-division. In paracrine signaling, the ligand diffuses to nearby cells and affects them. For example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. In juxtacrine signaling, there is direct contact between the signaling and responding cells. Finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. Once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. For instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. Other types of receptors include protein kinase receptors (e.g., receptor for the hormone insulin) and G protein-coupled receptors. Activation of G protein-coupled receptors can initiate second messenger cascades. The process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction

Cell cycle

The cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division.^[56] In eukaryotes (i.e., animal, plant, fungal, and protist cells), there are two distinct types of cell division: mitosis and meiosis.^[57] Mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA is replicated) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis all together define the mitotic phase of an animal cell cycle—the division of the mother cell into two genetically identical daughter cells.^[58] The cell cycle is a vital process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. After cell division, each of the daughter cells begin the interphase of a new cycle. In contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions.^[59] Homologous chromosomes are separated in the first division (meiosis I), and sister chromatids are separated in the second division (meiosis II). Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor.

Prokaryotes (i.e., archaea and bacteria) can also undergo cell division (or binary fission). Unlike the processes of mitosis and meiosis in eukaryotes, binary fission takes in prokaryotes takes place without the formation of a spindle apparatus on the cell. Before binary fission, DNA in the bacterium is tightly coiled. After it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. Growth of a new cell wall begins to separate the bacterium (triggered by FtsZ polymerization and «Z-ring» formation)^[60] The new cell wall (septum) fully develops, resulting in the complete split of the bacterium. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids.

Genetics

Inheritance

Genetics is the scientific study of inheritance.^[61][62][63] Mendelian inheritance, specifically, is the process by which genes and traits are passed on from parents to offspring.^[27] It has several principles. The first is that genetic characteristics, alleles, are discrete and have alternate forms (e.g., purple vs. white or tall vs. dwarf), each inherited from one of two parents. Based on the law of dominance and uniformity, which states that some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the phenotype of that dominant allele. During gamete formation, the alleles for each gene segregate, so that each gamete carries only one allele for each gene. Heterozygotic individuals produce gametes with an equal frequency of two alleles. Finally, the law of independent assortment, states that genes of different traits can segregate independently during the formation of gametes, i.e., genes are unlinked. An exception to this rule would include traits that are sex-linked. Test crosses can be performed to experimentally determine the underlying genotype of an organism with a dominant phenotype.^[64] A Punnett square can be used to predict the results of a test cross. The chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by Thomas Morgans’s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects.^[65]

Genes and DNA

Further information: Gene and DNA

A gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid (DNA) that carries genetic information that controls form or function of an organism. DNA is composed of two polynucleotide chains that coil around each other to form a double helix.^[66] It is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell is collectively known as its genome. In eukaryotes, DNA is mainly in the cell nucleus.^[67] In prokaryotes, the DNA is held within the nucleoid.^[68] The genetic information is held within genes, and the complete assemblage in an organism is called its genotype.^[69]
DNA replication is a semiconservative process whereby each strand serves as a template for a new strand of DNA.^[66] Mutations are heritable changes in DNA.^[66] They can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical (e.g., nitrous acid, benzopyrene) or radiation (e.g., x-ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes).^[66] Mutations can lead to phenotypic effects such as loss-of-function, gain-of-function, and conditional mutations.^[66]
Some mutations are beneficial, as they are a source of genetic variation for evolution.^[66] Others are harmful if they were to result in a loss of function of genes needed for survival.^[66] Mutagens such as carcinogens are typically avoided as a matter of public health policy goals.^[66]

Gene expression

Gene expression is the molecular process by which a genotype encoded in DNA gives rise to an observable phenotype in the proteins of an organism’s body. This process is summarized by the central dogma of molecular biology, which was formulated by Francis Crick in 1958.^[70][71][72] According to the Central Dogma, genetic information flows from DNA to RNA to protein. There are two gene expression processes: transcription (DNA to RNA) and translation (RNA to protein).^[73]

Gene regulation

The regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, RNA splicing, translation, and post-translational modification of a protein.^[74] Gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the DNA sequence close to or at a promoter.^[74] A cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes (e.g., Caenorhabditis elegans).^[74][75] In positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. Negative regulation occurs when another transcription factor called a repressor binds to a DNA sequence called an operator, which is part of an operon, to prevent transcription. Repressors can be inhibited by compounds called inducers (e.g., allolactose), thereby allowing transcription to occur.^[74] Specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active.^[74] In contrast to both, structural genes encode proteins that are not involved in gene regulation.^[74] In addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of DNA and protein found in eukaryotic cells.^[74]

Genes, development, and evolution

Development is the process by which a multicellular organism (plant or animal) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle.^[76] There are four key processes that underlie development: Determination, differentiation, morphogenesis, and growth. Determination sets the developmental fate of a cell, which becomes more restrictive during development. Differentiation is the process by which specialized cells from less specialized cells such as stem cells.^[77][78] Stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell.^[79] Cellular differentiation dramatically changes a cell’s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself.^[80] Thus, different cells can have very different physical characteristics despite having the same genome. Morphogenesis, or the development of body form, is the result of spatial differences in gene expression.^[76] A small fraction of the genes in an organism’s genome called the developmental-genetic toolkit control the development of that organism. These toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. Differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. Among the most important toolkit genes are the Hox genes. Hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva.^[81]

Evolution

Evolutionary processes

Evolution is a central organizing concept in biology. It is the change in heritable characteristics of populations over successive generations.^[82][83] In artificial selection, animals were selectively bred for specific traits.
^[84] Given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, Darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits.^[84] Darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals.^[84] He further inferred that this would lead to the accumulation of favorable traits over successive generations, thereby increasing the match between the organisms and their environment.^{[85][86][87][84][88]}

Speciation

A species is a group of organisms that mate with one another and speciation is the process by which one lineage splits into two lineages as a result of having evolved independently from each other.^[89] For speciation to occur, there has to be reproductive isolation.^[89] Reproductive isolation can result from incompatibilities between genes as described by Bateson–Dobzhansky–Muller model. Reproductive isolation also tends to increase with genetic divergence. Speciation can occur when there are physical barriers that divide an ancestral species, a process known as allopatric speciation.^[89]

Phylogeny

A phylogeny is an evolutionary history of a specific group of organisms or their genes.^[90] It can be represented using a phylogenetic tree, a diagram showing lines of descent among organisms or their genes. Each line drawn on the time axis of a tree represents a lineage of descendants of a particular species or population. When a lineage divides into two, it is represented as a fork or split on the phylogenetic tree.^[90] Phylogenetic trees are the basis for comparing and grouping different species.^[90] Different species that share a feature inherited from a common ancestor are described as having homologous features (or synapomorphy).^[91][92][90] Phylogeny provides the basis of biological classification.^[90] This classification system is rank-based, with the highest rank being the domain followed by kingdom, phylum, class, order, family, genus, and species.^[90] All organisms can be classified as belonging to one of three domains: Archaea (originally Archaebacteria); bacteria (originally eubacteria), or eukarya (includes the protist, fungi, plant, and animal kingdoms).^[93]

History of life

The history of life on Earth traces how organisms have evolved from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago and all life on Earth, both living and extinct, descended from a last universal common ancestor that lived about 3.5 billion years ago.^[94][95] Geologists have developed a geologic time scale that divides the history of the Earth into major divisions, starting with four eons (Hadean, Archean, Proterozoic, and Phanerozoic), the first three of which are collectively known as the Precambrian, which lasted approximately 4 billion years.^[96] Each eon can be divided into eras, with the Phanerozoic eon that began 539 million years ago^[97] being subdivided into Paleozoic, Mesozoic, and Cenozoic eras.^[96] These three eras together comprise eleven periods (Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary).^[96]

The similarities among all known present-day species indicate that they have diverged through the process of evolution from their common ancestor.^[98] Biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes.^{[99][10][100][101]} Microbal mats of coexisting bacteria and archaea were the dominant form of life in the early Archean epoch and many of the major steps in early evolution are thought to have taken place in this environment.^[102] The earliest evidence of eukaryotes dates from 1.85 billion years ago,^[103][104] and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions.^[105]

Algae-like multicellular land plants are dated back even to about 1 billion years ago,^[106] although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 billion years ago.^[107] Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician period. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event.^[108]

Ediacara biota appear during the Ediacaran period,^[109] while vertebrates, along with most other modern phyla originated about 525 million years ago during the Cambrian explosion.^[110] During the Permian period, synapsids, including the ancestors of mammals, dominated the land,^[111] but most of this group became extinct in the Permian–Triassic extinction event 252 million years ago.^[112] During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates;^[113] one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods.^[114] After the Cretaceous–Paleogene extinction event 66 million years ago killed off the non-avian dinosaurs,^[115] mammals increased rapidly in size and diversity.^[116] Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.^[117]

Diversity

Bacteria and Archaea

Bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. Typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste,^[118] and the deep biosphere of the earth’s crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory.^[119]

Archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), a term that has fallen out of use.^[120] Archaeal cells have unique properties separating them from the other two domains, Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla. Archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of Haloquadratum walsbyi.^[121] Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes,^[122] including archaeols. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria, no known species of Archaea form endospores.

The first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. Improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet.

Archaea are a major part of Earth’s life. They are part of the microbiota of all organisms. In the human microbiome, they are important in the gut, mouth, and on the skin.^[123] Their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles: carbon fixation; nitrogen cycling; organic compound turnover; and maintaining microbial symbiotic and syntrophic communities, for example.^[124]

Eukaryotes

Eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria (or symbiogenesis) that gave rise to mitochondria and chloroplasts, both of which are now part of modern-day eukaryotic cells.^[125] The major lineages of eukaryotes diversified in the Precambrian about 1.5 billion years ago and can be classified into eight major clades: alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals.^[125] Five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals.^[125] While it is likely that protists share a common ancestor (the last eukaryotic common ancestor),^[126] protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. Like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience.^[125][127] Most protists are unicellular; these are called microbial eukaryotes.^[125]

Plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom Plantae, which would exclude fungi and some algae. Plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts.^[128] The first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related.^[128] Algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of Plantae.^[128] Unlike glaucophytes, the other algal clades such as red and green algae are multicellular. Green algae comprise three major clades: chlorophytes, coleochaetophytes, and stoneworts.^[128]

Fungi are eukaryotes that digest foods outside their bodies,^[129] secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. Many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems.^[129]

Animals are multicellular eukaryotes. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. They have complex interactions with each other and their environments, forming intricate food webs.^[130]

Viruses

Viruses are submicroscopic infectious agents that replicate inside the cells of organisms.^[131] Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.^[132][133] More than 6,000 virus species have been described in detail.^[134] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.^[135][136]

The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction.^[137] Because viruses possess some but not all characteristics of life, they have been described as «organisms at the edge of life»,^[138] and as self-replicators.^[139]

Ecology

Ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment.^[140]

Ecosystems

The community of living (biotic) organisms in conjunction with the nonliving (abiotic) components (e.g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil) of their environment is called an ecosystem.^{[141][142][143]} These biotic and abiotic components are linked together through nutrient cycles and energy flows.^[144] Energy from the sun enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one another, animals move matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.^[145]

Populations

A population is the group of organisms of the same species that occupies an area and reproduce from generation to generation.^{[146][147][148][149][150]} Population size can be estimated by multiplying population density by the area or volume. The carrying capacity of an environment is the maximum population size of a species that can be sustained by that specific environment, given the food, habitat, water, and other resources that are available.^[151] The carrying capacity of a population can be affected by changing environmental conditions such as changes in the availability resources and the cost of maintaining them. In human populations, new technologies such as the Green revolution have helped increase the Earth’s carrying capacity for humans over time, which has stymied the attempted predictions of impending population decline, the most famous of which was by Thomas Malthus in the 18th century.^[146]

Communities

A community is a group of populations of species occupying the same geographical area at the same time. A biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or of different species (interspecific interactions). These effects may be short-term, like pollination and predation, or long-term; both often strongly influence the evolution of the species involved. A long-term interaction is called a symbiosis. Symbioses range from mutualism, beneficial to both partners, to competition, harmful to both partners.^[153] Every species participates as a consumer, resource, or both in consumer–resource interactions, which form the core of food chains or food webs.^[154] There are different trophic levels within any food web, with the lowest level being the primary producers (or autotrophs) such as plants and algae that convert energy and inorganic material into organic compounds, which can then be used by the rest of the community.^{[51][155][156]} At the next level are the heterotrophs, which are the species that obtain energy by breaking apart organic compounds from other organisms.^[154] Heterotrophs that consume plants are primary consumers (or herbivores) whereas heterotrophs that consume herbivores are secondary consumers (or carnivores). And those that eat secondary consumers are tertiary consumers and so on. Omnivorous heterotrophs are able to consume at multiple levels. Finally, there are decomposers that feed on the waste products or dead bodies of organisms.^[154]
On average, the total amount of energy incorporated into the biomass of a trophic level per unit of time is about one-tenth of the energy of the trophic level that it consumes. Waste and dead material used by decomposers as well as heat lost from metabolism make up the other ninety percent of energy that is not consumed by the next trophic level.^[157]

Biosphere

In the global ecosystem or biosphere, matter exists as different interacting compartments, which can be biotic or abiotic as well as accessible or inaccessible, depending on their forms and locations.^[159] For example, matter from terrestrial autotrophs are both biotic and accessible to other organisms whereas the matter in rocks and minerals are abiotic and inaccessible. A biogeochemical cycle is a pathway by which specific elements of matter are turned over or moved through the biotic (biosphere) and the abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. There are biogeochemical cycles for nitrogen, carbon, and water.

Conservation

Conservation biology is the study of the conservation of Earth’s biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.^{[160][161][162]} It is concerned with factors that influence the maintenance, loss, and restoration of biodiversity and the science of sustaining evolutionary processes that engender genetic, population, species, and ecosystem diversity.^{[163][164][165][166]} The concern stems from estimates suggesting that up to 50% of all species on the planet will disappear within the next 50 years,^[167] which has contributed to poverty, starvation, and will reset the course of evolution on this planet.^[168][169] Biodiversity affects the functioning of ecosystems, which provide a variety of services upon which people depend. Conservation biologists research and educate on the trends of biodiversity loss, species extinctions, and the negative effect these are having on our capabilities to sustain the well-being of human society. Organizations and citizens are responding to the current biodiversity crisis through conservation action plans that direct research, monitoring, and education programs that engage concerns at local through global scales.^{[170][163][164][165]}

See also

References

Further reading

External links

• Biology at Curlie
• OSU’s Phylocode
• Biology Online – Wiki Dictionary
• MIT video lecture series on biology
• OneZoom Tree of Life

Journal links

• PLOS Biology A peer-reviewed, open-access journal published by the Public Library of Science
• Current Biology: General journal publishing original research from all areas of biology
• Biology Letters: A high-impact Royal Society journal publishing peer-reviewed biology papers of general interest
• Science: Internationally renowned AAAS science journal – see sections of the life sciences
• International Journal of Biological Sciences: A biological journal publishing significant peer-reviewed scientific papers
• Perspectives in Biology and Medicine: An interdisciplinary scholarly journal publishing essays of broad relevance

English[edit]

Wikibooks

Etymology[edit]

A classical compound, being a naturalization into English via the German Biologie from the New Latin coinage biologia, with components derived from Ancient Greek βίος (bíos, “bio-, life”) +‎ -λογία (-logía, “-logy, branch of study, to speak”). The term *βιολογία (*biología) did not exist in Ancient Greek. The New Latin word was coined in the 18th century but did not yet have the sense that it now has. That sense was developed circa 1800 when the German word Biologie was naturalized from the New Latin word; see Wikipedia at Biology § Etymology for the details. The modern sibling cognates came into various European languages in the 19th century (e.g., French biologie, English biology). As the scientific era progressed in the 19th century, the modern surface analysis of the English word developed, as a compound using the combining forms bio- +‎ -logy. As for modern Greek βιολογία (viología): it is borrowed from both English and French biologie via international scientific vocabulary.

Pronunciation[edit]

• enPR: bī-ŏl′-əjē
• (Received Pronunciation) IPA^(key): /baɪˈɒl.ə.d͡ʒɪ/
• (General American) IPA^(key): /baɪˈɑ.lə.d͡ʒi/, /baɪˌɑl(ə)ˈd͡ʒi/
• Rhymes: -ɒlədʒi

Noun[edit]

biology (countable and uncountable, plural biologies)

1. The study of all life or living matter.

   • 2012 January 1, Robert M. Pringle, “How to Be Manipulative”, in American Scientist‎^[1], volume 100, number 1, page 31:

     As in much of biology, the most satisfying truths in ecology derive from manipulative experimentation. Tinker with nature and quantify how it responds.

2. The living organisms of a particular region.

   • 1893, “Prizes for original work with the microscope”, in Proceedings of the American Microscopical Society‎^[2], volume 14, page 38:

     The object of these prizes is to stimulate and encourage original investigation by the aid of the microscope in the biology of North America, and, while the competition is open to all, it is especially commended to advanced students in biology in such of our universities and colleges as furnish opportunity for suitable work.

3. The structure, function, and behavior of an organism or type of organism.

   the biology of the whale

Synonyms[edit]

• lifelore, life science, life sciences

Meronyms[edit]

• See also Thesaurus:biology

Derived terms[edit]

[edit]

• biological
• biologically
• biologic
• biologism
• biologist
• biologize

Translations[edit]

See also[edit]

• Category:Biology

The history of biology traces the study of the living world from ancient to modern times. Although the concept of biology as a single coherent field arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to Galen and Aristotle in ancient Greece. During the Renaissance and early modern period, biological thought was revolutionized by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Vesalius and Harvey, who used experimentation and careful observation in physiology, and naturalists such as Linnaeus and Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms. Microscopy revealed the previously unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology, partly a response to the rise of mechanical philosophy, encouraged the growth of natural history (although it entrenched the argument from design).

Over the 18th and 19th centuries, biological sciences such as botany and zoology became increasingly professional scientific disciplines. Lavoisier and other physical scientists began to connect the animate and inanimate worlds through physics and chemistry. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography—laying the foundations for biogeography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life. These developments, as well as the results from embryology and paleontology, were synthesized in Charles Darwin’s theory of evolution by natural selection. The end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery.

In the early 20th century, the rediscovery of Mendel’s work led to the rapid development of genetics by Thomas Hunt Morgan and his students, and by the 1930s the combination of population genetics and natural selection in the «neo-Darwinian synthesis». New disciplines developed rapidly, especially after Watson and Crick proposed the structure of DNA. Following the establishment of the Central Dogma and the cracking of the genetic code, biology was largely split between organismal biology—the fields that deal with whole organisms and groups of organisms—and the fields related to cellular and molecular biology. By the late 20th century, new fields like genomics and proteomics were reversing this trend, with organismal biologists using molecular techniques, and molecular and cell biologists investigating the interplay between genes and the environment, as well as the genetics of natural populations of organisms.

History of science
Background
Theories/sociology
Historiography
Pseudoscience
By era
In early cultures
in Classical Antiquity
In the Middle Ages
In the Renaissance
Scientific Revolution
By topic
Natural sciences
Astronomy
Biology
Chemistry
Ecology
Geography
Geology
Paleontology
Physics
Social sciences
Economics
Linguistics
Political science
Psychology
Sociology
Technology
Agricultural science
Computer science
Materials science
Medicine
Navigational pages
Timelines
Portal

Etymology of «biology»

The word biology is formed by combining the Greek βίος (bios), meaning «life», and the suffix ‘-logy’, meaning «science of», «knowledge of», «study of», based on the Greek verb λεγειν, ‘legein’ = «to select», «to gather» (cf. the noun λόγος, ‘logos’ = «word»). The term biology in its modern sense appears to have been introduced independently by Karl Friedrich Burdach (in 1800), Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and Jean-Baptiste Lamarck (Hydrogéologie, 1802).^[1][2] The word itself appears in the title of Volume 3 of Michael Christoph Hanov’s Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia, phytologia generalis et dendrologia, published in 1766.

Before biology, there were several terms used for the study of animals and plants. Natural history referred to the descriptive aspects of biology, though it also included mineralogy and other non-biological fields; from the Middle Ages through the Renaissance, the unifying framework of natural history was the scala naturae or Great Chain of Being. Natural philosophy and natural theology encompassed the conceptual and metaphysical basis of plant and animal life, dealing with problems of why organisms exist and behave the way they do, though these subjects also included what is now geology, physics, chemistry, and astronomy. Physiology and (botanical) pharmacology were the province of medicine. Botany, zoology, and (in the case of fossils) geology replaced natural history and natural philosophy in the 18th and 19th centuries before biology was widely adopted.^[3][4]

Ancient and medieval knowledge

Biological knowledge in early cultures

See also: History of the world and History of agriculture

The earliest humans must have had and passed on knowledge about plants and animals to increase their chances of survival. This may have included knowledge of human and animal anatomy and aspects of animal behavior (such as migration patterns). However, the first major turning point in biological knowledge came with the Neolithic Revolution about 10,000 years ago. Humans first domesticated plants for farming, then livestock animals to accompany the resulting sedentary societies.^[5]

The ancient cultures of Mesopotamia, Egypt, the Indian subcontinent, and China (among others) had sophisticated systems of philosophical, religious, and technical knowledge that encompassed the living world, and creation myths often centered on some aspect of life. However, the roots of modern biology are usually traced back to the secular tradition of ancient Greek philosophy.^[6]

Ancient Greek biological traditions

See also: Medicine in ancient Greece

The Pre-Socratic philosophers asked many questions about life but produced little systematic knowledge of specifically biological interest—though the attempts of the atomists to explain life in purely physical terms would recur periodically through the history of biology. However, the medical theories of Hippocrates and his followers, especially humorism, had a lasting impact.^[7]

The philosopher Aristotle was the most influential scholar of the living world from antiquity. Though his early work in natural philosophy was speculative, Aristotle’s later biological writings were more empirical, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, which he devoted considerable attention to categorizing. In all, Aristotle classified 540 animal species, and dissected at least 50. He believed that intellectual purposes, formal causes, guided all natural processes.^[8]

Aristotle, and nearly all scholars after him until the 18th century, believed that creatures were arranged in a graded scale of perfection rising from plants on up to humans: the scala naturae or Great Chain of Being.^[9] Aristotle’s successor at the Lyceum, Theophrastus, wrote a series of books on botany—the History of Plants—which survived as the most important contribution of antiquity to botany, even into the Middle Ages. Many of Theophrastus’ names survive into modern times, such as carpos for fruit, and pericarpion for seed vessel. Pliny the Elder was also known for his knowledge of plants and nature, and was the most prolific compiler of zoological descriptions.^[10]

A few scholars in the Hellenistic period under the Ptolemies—particularly Herophilus of Chalcedon and Erasistratus of Chios—amended Aristotle’s physiological work, even performing experimental dissections and vivisections.^[11] Claudius Galen became the most important authority on medicine and anatomy. Though a few ancient atomists such as Lucretius challenged the teleological Aristotelian viewpoint that all aspects of life are the result of design or purpose, teleology (and after the rise of Christianity, natural theology) would remain central to biological thought essentially until the 18th and 19th centuries. In the words of Ernst Mayr, «Nothing of any real consequence happened in biology after Lucretius and Galen until the Renaissance.»^[12] The ideas of the Greek traditions of natural history and medicine survived, but they were generally taken unquestioningly.^[13]

Medieval knowledge

The decline of the Roman Empire led to the disappearance or destruction of much knowledge, though physicians still incorporated many aspects of the Greek tradition into training and practice. In Byzantium and the Islamic world, many of the Greek works were translated into Arabic and many of the works of Aristotle were preserved. During the High Middle Ages, a few European scholars such as Hildegard of Bingen, Albertus Magnus, and Frederick II expanded the natural history canon. The rise of European universities, though important for the development of physics and philosophy, had little impact on biological scholarship.^[14]

Renaissance and early modern developments

See also: History of anatomy and Scientific Revolution

The European Renaissance brought expanded interest in both empirical natural history and physiology. In 1543, Andreas Vesalius inaugurated the modern era of Western medicine with his seminal human anatomy treatise De humani corporis fabrica, which was based on dissection of corpses. Vesalius was the first in a series of anatomists who gradually replaced scholasticism with empiricism in physiology and medicine, relying on first-hand experience rather than authority and abstract reasoning. Via herbalism, medicine was also indirectly the source of renewed empiricism in the study of plants. Otto Brunfels, Hieronymus Bock and Leonhart Fuchs wrote extensively on wild plants, the beginning of a nature-based approach to the full range of plant life.^[15] Bestiaries—a genre that combines both the natural and figurative knowledge of animals—also became more sophisticated, especially with the work of William Turner, Pierre Belon, Guillaume Rondelet, Conrad Gessner, and Ulisse Aldrovandi.^[16]

Artists such as Albrecht Dürer and Leonardo da Vinci, often working with naturalists, were also interested in the bodies of animals and humans, studying physiology in detail and contributing to the growth of anatomical knowledge.^[17] The traditions of alchemy and natural magic, especially in the work of Paracelsus, also laid claim to knowledge of the living world. Alchemists subjected organic matter to chemical analysis and experimented liberally with both biological and mineral pharmacology.^[18] This was part of a larger transition in world views (the rise of the mechanical philosophy) that continued into the 17th century, as the traditional metaphor of nature as organism was replaced by the nature as machine metaphor.^[19]

Seventeenth and eighteenth centuries

See also: History of plant systematics

Extending the work of Vesalius into experiments on still living bodies (of both humans and animals), William Harvey and other natural philosophers investigated the roles of blood, veins and arteries. Harvey’s De motu cordis in 1628 was the beginning of the end for Galenic theory, and alongside Santorio Santorio’s studies of metabolism, it served as an influential model of quantitative approaches to physiology.^[20]

In the early 17th century, the micro-world of biology was just beginning to open up. A few lensmakers and natural philosophers had been creating crude microscopes since the late 16th century, and Robert Hooke published the seminal Micrographia based on observations with his own compound microscope in 1665. But it was not until Antony van Leeuwenhoek’s dramatic improvements in lensmaking beginning in the 1670s—ultimately producing up to 200-fold magnification with a single lens—that scholars discovered spermatozoa, bacteria, infusoria and the sheer strangeness and diversity of microscopic life. Similar investigations by Jan Swammerdam led to new interest in entomology and built the basic techniques of microscopic dissection and staining.^[21]

As the microscopic world was expanding, the macroscopic world was shrinking. Botanists such as John Ray worked to incorporate the flood of newly discovered organisms shipped from across the globe into a coherent taxonomy, and a coherent theology (natural theology).^[22] Debate over another flood, the Noachian, catalyzed the development of paleontology; in 1669 Nicholas Steno published an essay on how the remains of living organisms could be trapped in layers of sediment and mineralized to produce fossils. Although Steno’s ideas about fossilization were well known and much debated among natural philosophers, an organic origin for all fossils would not be accepted by all naturalists until the end of the 18th century due to philosophical and theological debate about issues such as the age of the earth and extinction.^[23]

Systematizing, naming and classifying dominated natural history throughout much of the 17th and 18th centuries. Carolus Linnaeus published a basic taxonomy for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced scientific names for all his species.^[24] While Linnaeus conceived of species as unchanging parts of a designed hierarchy, the other great naturalist of the 18th century, Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent. Though he was opposed to evolution, Buffon is a key figure in the history of evolutionary thought; his work would influence the evolutionary theories of both Lamarck and Darwin.^[25]

The discovery and description of new species and the collection of specimens became a passion of scientific gentlemen and a lucrative enterprise for entrepreneurs; many naturalists traveled the globe in search of scientific knowledge and adventure.^[26]

Nineteenth century: the emergence of biological disciplines

Up through the nineteenth century, the scope of biology was largely divided between medicine, which investigated questions of form and function (i.e., physiology), and natural history, which was concerned with the diversity of life and interactions among different forms of life and between life and non-life. By 1900, much of these domains overlapped, while natural history and (and its counterpart natural philosophy) had largely given way to more specialized scientific disciplines—cytology, bacteriology, morphology, embryology, geography, and geology.

Natural history and natural philosophy

See also: Humboldtian science

Widespread travel by naturalists in the early- to mid-nineteenth century resulted in a wealth of new information about the diversity and distribution of living organisms. Of particular importance was the work of Alexander von Humboldt, which analyzed the relationship between organisms and their environment (i.e., the domain of natural history) using the quantitative approaches of natural philosophy (i.e., physics and chemistry). Humboldt’s work laid the foundations of biogeography and inspired several generations of scientists.^[27]

Geology and paleontology

See also: History of geology and History of paleontology

The emerging discipline of geology also brought natural history and natural philosophy closer together; the establishment of the stratigraphic column linked the spacial distribution of organisms to their temporal distribution, a key precursor to concepts of evolution. Georges Cuvier and others made great strides in comparative anatomy and paleontology in the late 1790s and early 1800s. In a series of lectures and papers that made detailed comparisons between living mammals and fossil remains Cuvier was able to establish that the fossils were remains of species that had become extinct—rather than being remains of species still alive elsewhere in the world, as had been widely believed.^[28] Fossils discovered and described by Gideon Mantell, William Buckland, Mary Anning, and Richard Owen among others helped establish that there had been an ‘age of reptiles’ that had preceded even the prehistoric mammals. These discoveries captured the public imagination and focused attention on the history of life on earth.^[29] Most of these geologists held to catastrophism, but Charles Lyell’s influential Principles of Geology (1830) popularised Hutton’s uniformitarianism, a theory that explained the geological past and present on equal terms.^[30]

Evolution and biogeography

See also: History of evolutionary thought

The most significant evolutionary theory before Darwin’s was that of Jean-Baptiste Lamarck; based on the inheritance of acquired characteristics (an inheritance mechanism that was widely accepted until the 20th century), it described a chain of development stretching from the lowliest microbe to humans.^[31] The British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Thomas Malthus’s writings on population growth, and his own morphological expertise, created a more successful evolutionary theory based on natural selection; similar evidence lead Alfred Russel Wallace to independently reach the same conclusions.^[32]

The 1859 publication of Darwin’s theory in On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life is often considered the central event in the history of modern biology. Darwin’s established credibility as a naturalist, the sober tone of the work, and most of all the sheer strength and volume of evidence presented, allowed Origin to succeed where previous evolutionary works such as the anonymous Vestiges of Creation had failed. Most scientists were convinced of evolution and common descent by the end of the 19th century. However, natural selection would not be accepted as the primary mechanism of evolution until well into the 20th century, as most contemporary theories of heredity seemed incompatible with the inheritance of random variation.^[33]

Wallace, following on earlier work by de Candolle, Humbolt and Darwin, made major contributions to zoogeography. Because of his interest in the transmutation hypothosis, he paid particular attention to the geographical distribution of closely allied species during his field work first in South America and then in the Malay archipelago. While in the archipelago he identified the Wallace line, which runs through the spice islands dividing the fauna of the archipelago between an Asian zone and a New Guinea/Australian zone. His key question, as to why the fauna of islands with such similar climates should be so different, could only be answered by considering their origin. In 1876 he wrote The geographical distribution of animals, which was the standard reference work for over half a century, and a sequel, Island Life, in 1880 that focused on island biogeography. He extended the 6 zone system developed by Philip Sclater for describing the geographical distribution of birds to animals of all kinds. His method of tabulating data on animal groups in geographic zones highlighted the discontinuities; and his appreciation of evolution allowed him to propose rational explanations, which had not been done before.^[34][35]

The scientific study of heredity grew rapidly in the wake of Darwin’s Origin of Species with the work of Francis Galton and the biometricians. The origin of genetics is usually traced to the 1866 work of the monk Gregor Mendel, who would later be credited with the laws of inheritance. However, his work was not recognized as significant until 35 years afterward. In the meantime, a variety of theories of inheritance (based on pangenesis, orthogenesis, or other mechanisms) were debated and investigated vigorously.^[36] Embryology and ecology also became central biological fields, especially as linked to evolution and popularized in the work of Ernst Haeckel. Most of the 19th century work on heredity, however, was not in the realm of natural history, but that of experimental physiology.

Physiology

Over the course of the 19th century, the scope of physiology expanded greatly, from a primarily medically-oriented field to a wide-ranging investigation of the physical and chemical processes of life—including plants, animals, and even microorganisms in addition to man. Living things as machines became a dominant metaphor in biological (and social) thinking.^[37]

Cell theory, embryology and germ theory

Advances in microscopy also had a profound impact on biological thinking. In the early 19th century, a number of biologists pointed to the central importance of the cell. In 1838 and 1839, Schleiden and Schwann began promoting the ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, though they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory.^[38]

Cell theory led biologists to re-envision individual organisms as interdependent assemblages of individual cells. Scientists in the rising field of cytology, armed with increasingly powerful microscopes and new staining methods, soon found that even single cells were far more complex than the homogeneous fluid-filled chambers of described by earlier microscopists. Robert Brown had described the nucleus in 1831, and by the end of the 19th century cytologists identified many of the key cell components: chromosomes, centrosomes mitochondria, chloroplasts, and other structures made visible through staining. Between 1874 and 1884 Walther Flemming described the discrete stages of mitosis, showing that they were not artifacts of staining but occurred in living cells, and moreover, that chromosomes doubled in number just before the cell divided and a daughter cell was produced. Much of the research on cell reproduction came together in August Weismann’s theory of heredity: he identified the nucleus (in particular chromosomes) as the hereditary material, proposed the distinction between somatic cells and germ cells (arguing that chromosome number must be halved for germ cells, a precursor to the concept of meiosis), and adopted Hugo de Vries’s theory of pangenes. Weismannism was extremely influential, especially in the new field of experimental embryology.^[39]

By the mid 1850s the miasma theory of disease was largely superseded by the germ theory of disease, creating extensive interest in microorganisms and their interactions with other forms of life. By the 1880s, bacteriology was becoming a coherent discipline, especially through the work of Robert Koch, who introduced methods for growing pure cultures on agar gels containing specific nutrients in Petri dishes. The long-held idea that living organisms could easily originate from nonliving matter (spontaneous generation) was attacked in a series of experiments carried out by Louis Pasteur, while debates over vitalism vs. mechanism (a perennial issue since the time of Aristotle and the Greek atomists) continued apace.^[40]

Rise of organic chemistry and experimental physiology

In chemistry, one central issue was the distinction between organic and inorganic substances, especially in the context of organic transformations such as fermentation and putrefaction. Since Aristotle these had been considered essentially biological (vital) processes. However, Friedrich Wöhler, Justus Liebig and other pioneers of the rising field of organic chemistry—building on the work of Lavoisier—showed that the organic world could often be analyzed by physical and chemical methods. In 1828 Wöhler showed that the organic substance urea could be created by chemical means that do not involve life, providing a powerful argument against vitalism. Cell extracts («ferments») that could effect chemical transformations were discovered, beginning with diastase in 1833, and by the end of the 19th century the concept of enzymes was well established, though equations of chemical kinetics would not be applied to enzymatic reactions until the early 20th century.^[41]

Physiologists such as Claude Bernard explored (through vivisection and other experimental methods) the chemical and physical functions of living bodies to an unprecedented degree, laying the groundwork for endocrinology (a field that developed quickly after the discovery of the first hormone, secretin, in 1902), biomechanics, and the study of nutrition and digestion. The importance and diversity of experimental physiology methods, within both medicine and biology, grew dramatically over the second half of the 19th century. The control and manipulation of life processes became a central concern, and experiment was placed at the center of biological education.^[42]

Twentieth century biological sciences

At the beginning of the 20th century, biological research was largely a professional endeavour. However, most work was still done in the natural history mode, which emphasized morhphological and phylogenetic analysis over experiment-based causal explanations. However, anti-vitalist experimental physiologists and embryologists, especially in Europe, were increasingly influential. The tremendous success of experimental approaches to development, heredity, and metabolism in the 1900s and 1910s demonstrated the power of experimentation in biology. In the following decades, experimental work replaced natural history as the dominant mode of research.^[43]

Ecology and environmental science

See also: History of ecology

In the early 20th century, naturalists were faced with increasing pressure to add rigor and preferably experimentation to their methods, as the newly prominent laboratory-based biological disciplines had done. Ecology had emerged as a combination of biogeography with the biogeochemical cycle concept pioneered by chemists; field biologists developed quantitative methods such as the quadrat and adapted laboratory instruments and cameras for the field to further set their work apart from traditional natural history. Zoologists and botanists did what they could to mitigate the unpredictability of the living world, performing laboratory experiments and studying semi-controlled natural environments such as gardens; new institutions like the Carnegie Station for Experimental Evolution and the Marine Biological Laboratory provided more controlled environments for studying organisms through their entire life cycles.^[44]

The ecological succession concept, pioneered in the 1900s and 1910s by Henry Chandler Cowles and Frederic Clements, was important in early plant ecology. Alfred Lotka’s predator-prey equations, G. Evelyn Hutchinson’s studies of the biogeography and biogeochemical structure of lakes and rivers (limnology) and Charles Elton’s studies of animal food chains were pioneers among the succession of quantitative methods that colonized the developing ecological specialties. Ecology became an independent discipline in the 1940s and 1950s after Eugene P. Odum synthesized many of the concepts of ecosystem ecology, placing relationships between groups of organisms (especially material and energy relationships) at the center of the field.^[45]

In the 1960s, as evolutionary theorists explored the possibility of multiple units of selection, ecologists turned to evolutionary approaches. In population ecology, debate over group selection was brief but vigorous; by 1970, most biologists agreed that natural selection was rarely effective above the level of individual organisms. The evolution of ecosystems, however, became a lasting research focus. Ecology expanded rapidly with the rise of the environmental movement; the International Biological Program attempted to apply the methods of big science (which had been so successful in the physical sciences) to ecosystem ecology and pressing environmental issues, while smaller-scale independent efforts such as island biogeography and the Hubbard Brook Experimental Forest helped redefine the scope of an increasingly diverse discipline.^[46]

Classical genetics, the modern synthesis, and evolutionary theory

See also: History of genetics, History of model organisms, and Modern evolutionary synthesis

 
1900 marked the so-called rediscovery of Mendel: Hugo de Vries, Carl Correns, and Erich von Tschermak independently arrived at Mendel’s laws (which were not actually present in Mendel’s work).^[47] Soon after, cytologists (cell biologists) proposed that chromosomes were the hereditary material. Between 1910 and 1915, Thomas Hunt Morgan and the «Drosophilists» in his fly lab forged these two ideas—both controversial—into the «Mendelian-chromosome theory» of heredity.^[48] They quantified the phenomenon of genetic linkage and postulated that genes reside on chromosomes like beads on string; they hypothesized crossing over to explain linkage and constructed genetic maps of the fruit fly Drosophila melanogaster, which became a widely used model organism.^[49]

Hugo de Vries tried to link the new genetics with evolution; building on his work with heredity and hybridization, he proposed a theory of mutationism, which was widely accepted in the early 20th century. Lamarckism also had many adherents. Darwinism was seen as incompatible with the continuously variable traits studied by biometricians, which seemed only partially heritable. In the 1920s and 1930s—following the acceptance of the Mendelian-chromosome theory— the emergence of the discipline of population genetics, with the work of R.A. Fisher, J.B.S. Haldane and Sewall Wright, unified the idea of evolution by natural selection with Mendelian genetics, producing the modern synthesis. The inheritance of acquired characters was rejected, while mutationism gave way as genetic theories matured.^[50]

In the second half of the century the ideas of population genetics began to be applied in the new discipline of the genetics of behavior, sociobiology, and, especially in humans, evolutionary psychology. In the 1960s W.D. Hamilton and others developed game theory approaches to explain altruism from an evolutionary perspective through kin selection. The possible origin of higher organisms through endosymbiosis, and contrasting approaches to molecular evolution in the gene-centered view (which held selection as the predominant cause of evolution) and the neutral theory (which made genetic drift a key factor) spawned perennial debates over the proper balance of adaptationism and contingency in evolutionary theory.^[51]

In the 1970s Stephen Jay Gould and Niles Eldredge proposed the theory of punctuated equilibrium which holds that stasis is the most prominent feature of the fossil record, and that most evolutionary changes occur rapidly over relatively short periods of time.^[52] In 1980 Luis Alvarez and Walter Alvarez proposed the hypothesis that an impact event was responsible for the Cretaceous-Tertiary extinction event.^[53] Also in the early 1980s, statistical analysis of the fossil record of marine organisms published by Jack Sepkoski and David M. Raup lead to a better appreciation of the importance of mass extinction events to the history of life on earth.^[54]

Biochemistry, microbiology, and molecular biology

See also: History of biochemistry and History of molecular biology

By the end of the 19th century all of the major pathways of drug metabolism had been discovered, along with the outlines of protein and fatty acid metabolism and urea synthesis.^[55] In the early decades of the twentieth century, the minor components of foods in human nutrition, the vitamins, began to be isolated and synthesized. Improved laboratory techniques such as chromatography and electrophoresis led to rapid advances in physiological chemistry, which—as biochemistry—began to achieve independence from its medical origins. In the 1920s and 1930s, biochemists—led by Hans Krebs and Carl and Gerty Cori—began to work out many of the central metabolic pathways of life: the citric acid cycle, glycogenesis and glycolysis, and the synthesis of steroids and porphyrins. Between the 1930s and 1950s, Fritz Lipmann and others established the role of ATP as the universal carrier of energy in the cell, and mitochondria as the powerhouse of the cell. Such traditionally biochemical work continued to be very actively pursued throughout the 20th century and into the 21st.^[56]

Origins of molecular biology

Following the rise of classical genetics, many biologists—including a new wave of physical scientists in biology—pursued the question of the gene and its physical nature. Warren Weaver—head of the science division of the Rockefeller Foundation—issued grants to promote research that applied the methods of physics and chemistry to basic biological problems, coining the term molecular biology for this approach in 1938; many of the significant biological breakthroughs of the 1930s and 1940s were funded by the Rockefeller Foundation.^[57]

Like biochemistry, the overlapping disciplines of bacteriology and virology (later combined as microbiology), situated between science and medicine, developed rapidly in the early 20th century. Félix d’Herelle’s isolation of bacteriophage during World War I initiated a long line of research focused of phage viruses and the bacteria they infect.^[58]

The development of standard, genetically uniform organisms that could produce repeatable experimental results was essential for the development of molecular genetics. After early work with Drosophila and maize, the adoption of simpler model systems like the bread mold Neurospora crassa made it possible to connect genetics to biochemistry, most importantly with Beadle and Tatum’s «one gene, one enzyme» hypothesis in 1941. Genetics experiments on even simpler systems like tobacco mosaic virus and bacteriophage, aided by the new technologies of electron microscopy and ultracentrifugation, forced scientists to re-evaluate the literal meaning of life; virus heredity and reproducing nucleoprotein cell structures outside the nucleus («plasmagenes») complicated the accepted Mendelian-chromosome theory.^[59]

Oswald Avery showed in 1943 that DNA was likely the genetic material of the chromosome, not its protein; the issue was settled decisively with the 1952 Hershey-Chase experiment—one of many contribution from the so-called phage group centered around physicist-turned-biologist Max Delbrück. In 1953 James D. Watson and Francis Crick, building on the work of Maurice Wilkins and Rosalind Franklin, suggested that the structure of DNA was a double helix. In their famous paper «Molecular structure of Nucleic Acids», Watson and Crick noted coyly, «It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.»^[61] After the 1958 Meselson-Stahl experiment confirmed the semiconservative replication of DNA, it was clear to most biologists that nucleic acid sequence must somehow determine amino acid sequence in proteins; physicist George Gamow proposed that a fixed genetic code connected proteins and DNA. Between 1953 and 1961, there were few known biological sequences—either DNA or protein—but an abundance of proposed code systems, a situation made even more complicated by expanding knowledge of the intermediate role of RNA. To actually decipher the code, it took an extensive series of experiments in biochemistry and bacterial genetics, between 1961 and 1966—most importantly the work of Nirenberg and Khorana.^[62]

Expansion of molecular biology

In addition to the Division of Biology at Caltech, the Laboratory of Molecular Biology (and its precursors) at Cambridge, and a handful of other institutions, the Pasteur Institute became a major center for molecular biology research in the late 1950s.^[63] Scientists at Cambridge, led by Max Perutz and John Kendrew, focused on the rapidly developing field of structural biology, combining X-ray crystallography with molecular modelling and the new computational possibilities of digital computing (benefiting both directly and indirectly from the military funding of science). A number of biochemists led by Fred Sanger later joined the Cambridge lab, bringing together the study of macromolecular structure and function.^[64] At the Pasteur Institute, François Jacob and Jacques Monod followed the 1959 PaJaMo experiment with a series of publications regarding the lac operon that established the concept of gene regulation and identified what came to be known as messenger RNA.^[65] By the mid-1960s, the intellectual core of molecular biology—a model for the molecular basis of metabolism and reproduction— was largely complete.^[66]

The late 1950s to the early 1970s was a period of intense research and institutional expansion for molecular biology, which had only recently become a somewhat coherent discipline. In what organismic biologist E. O. Wilson called «The Molecular Wars», the methods and practitioners of molecular biology spread rapidly, often coming to dominate departments and even entire disciplines.^[67] Molecularization was particularly important in genetics, immunology, embryology, and neurobiology, while the idea that life is controlled by a «genetic program»—a metaphor Jacob and Monod introduced from the emerging fields of cybernetics and computer science—became an influential perspective throughout biology.^[68] Immunology in particular became linked with molecular biology, with innovation flowing both ways: the clonal selection theory developed by Niels Jerne and Frank Macfarlane Burnet in the mid 1950s helped shed light on the general mechanisms of protein synthesis.^[69]

Resistance to the growing influence molecular biology was especially evident in evolutionary biology. Protein sequencing had great potential for the quantitative study of evolution (through the molecular clock hypothesis), but leading evolutionary biologists questioned the relevance of molecular biology for answering the big questions of evolutionary causation. Departments and disciplines fractured as organismic biologists asserted their importance and independence: Theodosius Dobzhansky made the famous statement that «nothing in biology makes sense except in the light of evolution» as a response to the molecular challenge. The issue became even more critical after 1968; Motoo Kimura’s neutral theory of molecular evolution suggested that natural selection was not the ubiquitous cause of evolution, at least at the molecular level, and that molecular evolution might be a fundamentally different process from morphological evolution. (Resolving this «molecular/morphological paradox» has been a central focus of molecular evolution research since the 1960s.)^[70]

Biotechnology, genetic engineering, and genomics

See also: History of biotechnology

Biotechnology in the general sense has been an important part of biology since the late 19th century. With the industrialization of brewing and agriculture, chemists and biologists became aware of the great potential of human-controlled biological processes. In particular, fermentation proved a great boon to chemical industries. By the early 1970s, a wide range of biotechnologies were being developed, from drugs like penicillin and steroids to foods like Chlorella and single-cell protein to gasohol—as well as a wide range of hybrid high-yield crops and agricultural technologies, the basis for the Green Revolution.^[71]

Recombinant DNA

Biotechnology in the modern sense of genetic engineering began in the 1970s, with the invention of recombinant DNA techniques. Restriction enzymes were discovered and characterized in the late 1960s, following on the heels of the isolation, then duplication, then synthesis of viral genes. Beginning with the lab of Paul Berg in 1972 (aided by EcoRI from Herbert Boyer’s lab, building on work with ligase by Arthur Kornberg’s lab), molecular biologists put these pieces together to produce the first transgenic organisms. Soon after, others began using plasmid vectors and adding genes for antibiotic resistance, greatly increasing the reach of the recombinant techniques.^[72]

Wary of the potential dangers (particularly the possibility of a prolific bacteria with a viral cancer-causing gene), the scientific community as well as a wide range of scientific outsiders reacted to these developments with both enthusiasm and fearful restraint. Prominent molecular biologists led by Berg suggested a temporary moratorium on recombinant DNA research until the dangers could be assessed and policies could be created. This moratorium was largely respected, until the participants in the 1975 Asilomar Conference on Recombinant DNA created policy recommendations and concluded that the technology could be used safely.^[73]

Following Asilomar, new genetic engineering techniques and applications developed rapidly. DNA sequencing methods improved greatly (pioneered by Fred Sanger and Walter Gilbert), as did oligonucleotide synthesis and transfection techniques.^[74] Researchers learned to control the expression of transgenes, and were soon racing—in both academic and industrial contexts—to create organisms capable of expressing human genes for the production of human hormones. However, this was a more daunting task than molecular biologists had expected; developments between 1977 and 1980 showed that, due to the phenomena of split genes and splicing, higher organisms had a much more complex system of gene expression than the bacteria models of earlier studies.^[75] The first such race, for synthesizing human insulin, was won by Genentech. This marked the beginning of the biotech boom (and with it, the era of gene patents), with an unprecedented level of overlap between biology, industry, and law.^[76]

Molecular systematics and genomics

See also: History of molecular evolution

By the 1980s, protein sequencing had already transformed methods of scientific classification of organisms (especially cladistics) but biologists soon began to use RNA and DNA sequences as characters; this expanded the significance of molecular evolution within evolutionary biology, as the results of molecular systematics could be compared with traditional evolutionary trees based on morphology. Following the pioneering ideas of Lynn Margulis on endosymbiotic theory, which holds that some of the organelles of eukaryotic cells originated from free living prokaryotic organisms through symbiotic relationships, even the overall division of the tree of life was revised. Into the 1990s, the five domains (Plants, Animals, Fungi, Protists, and Monerans) became three (the Archaea, the Bacteria, and the Eukarya) based on Carl Woese’s pioneering molecular systematics work with 16S rRNA sequencing.^[77]

The development and popularization of the polymerase chain reaction (PCR) in mid 1980s (by Kary Mullis and others at Cetus Corp.) marked another watershed in the history of modern biotechnology, greatly increasing the ease and speed of genetic analysis. Coupled with the use of expressed sequence tags, PCR led to the discovery of many more genes than could be found through traditional biochemical or genetic methods and opened the possibility of sequencing entire genomes.^[78]

The unity of much of the morphogenesis of organisms from fertilized egg to adult began to be unraveled after the discovery of the homeobox genes, first in fruit flies, then in other insects and animals, including humans. These developments led to advances in the field of evolutionary developmental biology towards understanding how the various body plans of the animal phyla have evolved and how they are related to one another.^[79]

The Human Genome Project—the largest, most costly single biological study ever undertaken—began in 1988 under the leadership of James D. Watson, after preliminary work with genetically simpler model organisms such as E. coli, S. cerevisiae and C. elegans. Shotgun sequencing and gene discovery methods pioneered by Craig Venter—and fueled by the financial promise of gene patents with Celera Genomics— led to a public-private sequencing competition that ended in compromise with the first draft of the human DNA sequence announced in 2000.^[80]

Notes

References