History of biology

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Like the tree of life itself, the history of biology is complex and many-branched.

The history of biology traces human understanding of the living world from the earliest recorded history to modern times. Though the concept of biology as a single coherent field of knowledge only arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to the ancient Greeks (particularly Galen and Aristotle, respectively). During the Renaissance and Age of Discovery, renewed interest in empiricism as well as the rapidly increasing number of known organisms led to significant developments in biological thought; Vesalius inaugurated the rise of experimentation and careful observation in physiology, and a series of naturalists culminating with Linnaeus and Buffon began to create a conceptual framework for analyzing the diversity of life and the fossil record, as well as the development and behavior of plants and animals. The growing importance of natural theology—partly a response to the rise of mechanical philosophy—was also an important impetus for the growth of natural history (though it also further entrenched the argument from design).

In the 18th century many fields of science—including botany, zoology, and geology—began to professionalize, forming the precursors of scientific disciplines in the modern sense (though the process would not be complete until the late 1800s). Lavoisier and other physical scientists began to connect the animate and inanimate worlds through the techniques and theory of physics and chemistry. Into the 19th century, explorer-naturalists such as Alexander von Humboldt tried to elucidate the interactions between organisms and their environment, and the ways these relationships depend on geography—creating the foundations for biogeography, ecology and ethology. Many naturalists began to reject essentialism and seriously consider the possibilities of extinction and the mutability of species. These developments, as well as the results of new fields such as embryology and paleontology, were synthesized in Darwin's theory of evolution by natural selection. The end of the 19th century saw debates over spontaneous generation and the rise of the germ theory of disease and the fields of cytology, bacteriology and physiological chemistry, though the problem of inheritance was still 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 led to the "neo-Darwinian synthesis" and the rise of the discipline of evolutionary biology. New biological disciplines developed rapidly, especially after Watson and Crick discovered the structure of DNA in 1953. Following the establishment of the Central Dogma and the cracking of the genetic code, biology was largely split between organismal biology—consisting of ecology, ethology, systematics, paleontology, evolutionary biology, developmental biology, and other disciplines that deal with whole organisms or groups of organisms—and the constellation of disciplines related to molecular biology—including cell biology, biophysics, biochemistry, neuroscience, immunology, and many other overlapping subjects. By the late 20th century, new fields like genomics and proteomics were reversing this trend; organismal biologists increasingly turned to molecular techniques and styles of thought, and molecular and cell biologists increasingly focused on the interplay between genes and the natural environment, as well as the genetic heterogeneity of natural populations such as humans.

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[edit] Etymology

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).

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 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 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 century before biology was widely adopted.

[edit] Ancient and medieval knowledge

[edit] Biological knowledge in early cultures

See also: History of agriculture

From early times, perhaps predating the appearance of modern humans, people must have had and passed on knowledge about plants and animals to increase their chances of survival. For example, they had to know how to avoid (or sometimes use) poisonous plants and animals and how to track, capture, and butcher different species of animals. They had to know which plants could be prepared to make good nets or baskets. In this sense, biology predates the written history of humans.

Agriculture requires specialised knowledge on plants and animals. Ancient Oriental people knew about the pollination of date palm from a very early point of time. In Mesopotamia they knew that pollen could be used in fertilizing plants. A business contract of the Hammurabi period (c. 1800 BCE) mentions flowers of the date palm as an article of commerce.

Frontispiece to a 1644 version of the expanded and illustrated edition of Historia Plantarum (ca. 1200), which was originally written around 200 BC

[edit] Classical Greek biology

The ancient Greek philosopher Aristotle was the most influential scholar of the living world from antiquity. Though his early natural philosophy work was speculative, Aristotle's later biological writings demonstrate great concern for empiricism, 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.^[1]

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 man: the scala naturae or Great Chain of Being.^[2] 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. Rather than focus on formal causes, as Aristotle did, Theophrastus suggested a mechanistic scheme, drawing analogies between natural and artificial processes, and relying on Aristotle's concept of the efficient cause. Theophrastus also recognized the role of sex in the reproduction of some higher plants, though this last discovery was lost in later ages.^[3]

[edit] Hellenistic biology

Following Theophrastus, the Lyceum failed to produce any original work. Though interest in Aristotle's ideas survived, they were generally taken unquestioningly.^[4] It is not until the age of Alexandria under the Ptolemies that advances in biology can be again found. The first medical teacher at Alexandria was Herophilus of Chalcedon, who corrected Aristotle, placing intelligence in the brain, and connected the nervous system to motion and sensation. Herophilus also distinguished between veins and arteries, noting that the latter pulse while the former do not.^[5] In the same vein, he developed a diagnostic technique which relied upon distinguishing different types of pulse.^[6] He, and his contemporary, Erasistratus of Chios, researched the role of veins and nerves, mapping their courses across the body.

Erasistratus connected the increased complexity of the surface of the human brain compared to other animals to its superior intelligence. He sometimes employed experiments to further his research, at one time repeatedly weighing a caged bird, and noting its weight loss between feeding times. Following his teacher's researches into pneumatics, he claimed that the human system of blood vessels was controlled by vacuums, drawing blood across the body. In Erisistratus' physiology, air enters the body, is then drawn by the lungs into the heart, where it is transformed into vital spirit, and is then pumped by the arteries throughout the body. Some of this vital spirit reaches the brain, where it is transformed into animal spirit, which is then distributed by the nerves.^[7] Herophilus and Erasistratus performed their experiments upon criminals given them by their Ptolemaic kings. They dissected these criminals alive, and "while they were still breathing they observed parts which nature had formerly concealed, and examined their position, colour, shape, size, arrangement, hardness, softness, smoothness, connection."^[8]

In ancient Rome, Pliny the Elder was known for his knowledge of plants and nature. Later, Claudius Galen became a pioneer in medicine and anatomy.

[edit] Medieval knowledge

The decline of the Roman Empire led to the disappearance or destruction of much knowledge. This time is often called the dark ages. However, some people who dealt with medical issues still studied plants and animals as well. In Byzantium and the Islamic world, natural philosophy was kept alive. Many of the Greek works were translated into Arabic and many of the works of Aristotle were preserved. Of the Arab biologists, al-Jahiz, who died about 868, is particularly noteworthy. He wrote Kitab al Hayawan (Book of animals). In the 1200s the German scholar named Albertus Magnus wrote De vegetabilibus, seven books, and De animalibus, 26 books. He was particularly interested in plant propagation and reproduction and discussed in some detail the sexuality of plants and animals.

[edit] The Renaissance

Albrecht Dürer's woodcut of a rhinoceros, an animal he had never actually seen

Interestingly, as many visual artists were interested in the bodies of animals and humans, they studied the physiology in detail. Such comparisons as that between a horse leg and a human leg were made. Otto Brunfels, Hieronymus Bock (also known as Hieronymus Tragus) and Leonhart Fuchs were three men who wrote books about wild plants; they have been referred to as the fathers of German botany. Books about animals were also made, such as those by Conrad Gesner, illustrated by, among others, Albrecht Dürer.

[edit] Seventeenth and eighteenth century developments

See also: History of plant systematics

Cabinets of curiosities, such as that of Ole Worm, were centers of biological knowledge in the early modern period, bringing organisms from across the world together in one place. Before the Age of Exploration, naturalists had little idea of the sheer scale of biological diversity.

In 1628 William Harvey explained that blood circulates throughout the body, and is pumped by the heart. Antony van Leeuwenhoek's invention of the microscope in about 1650 opened up the micro-world of biology. The History of Plants was greatly extended, almost into an encyclopedia, by Giovanni Bodeo da Stapel in 1644 AD. In 1658 Jan Swammerdam was the first to observe and describe red blood cells, while Leeuwenhoek was the first to describe spermatozoa, bacteria and infusoria in the 1670s and 1680s. By the 1690s plants were, like animals, known to be sexual, having stamens and pistils.

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, the role of the Noachian flood, and extinction. ^[9]

Systematizing, naming and classifying dominated biology throughout much of the 17th and 18th centuries. Carolus Linnaeus published a basic taxonomy for the natural world in 1735, and in the 1750s introduced scientific names for all his species. The discovery and description of new species, and collecting specimens became a widespread passion of scientific gentlemen.

[edit] 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.

[edit] Physiology

Wöhler showed In 1828 that organic molecules, such as urea, can be created by synthetic means that do not involve life, and thus provided a powerful argument against vitalism. The first enzyme, diastase, was described in 1833, and scientists began to explore connections between chemistry and biology.

Advances in microscopy also had a profound impact on biological thinking: in 1839, Schleiden and Schwann proposed the cell theory—that the basic unit of organisms is the cell and all cells come from preexisting cells. The cytologist Walther Flemming in 1882 was the first to demonstrate that the discrete stages of mitosis were not an artifact 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. In 1887 August Weismann proposed that the chromosome number must then be halved in the case of the sexual cells, the gametes. This was shortly proved to be the case and the process of meiosis began to be understood.

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 continued apace.

[edit] Natural history and natural philosophy

See also: Humboldtian science

In the course of his travels, Alexander von Humboldt mapped the distribution of plants across landscapes and recorded a variety of physical conditions such as pressure and temperature.

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.^[10]

[edit] 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^[11]. 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.^[12] Most of these geologists held to catastrophism, but Charles Lyell's influential Principles of Geology (1830) introduced uniformitarianism, a theory that explained the geological past and present on equal terms.^[13]

[edit] Evolution and biogeography

See also: History of evolutionary thought

Charles Darwin's first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837)

The first to propose an evolutionary theory was 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.^[14] 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.^[15] Similar evidence lead Alfred Wallace to independently reach the same conclusions.^[16] Though natural selection would not be accepted as the primary mechanism of evolution until well into the 20th century, most scientists were convinced of evolution and common descent by the end of the 19th century.^[17]

Alfred Wallace, building on earlier work by Humbolt and Darwin, made major contributions to biogeography by focusing on the distribution of closely allied species with particular attention to the effects of geographical barriers during his research in the Amazon basin and the Malay archipelago. He discovered the Wallace line dividing the fauna of the Malay archipelago between a zone allied with Asia and a zone allied with Australia. The orinthologist Philip Sclater, drawing on the work of Wallace and others, proposed a system of 6 major geographical regions to describe the distribution of bird species in the world. Wallace and others would in turn extend Sclater's system from birds to animals of all kinds. ^[18]

[edit] Heredity and development

The study of scientific study of heredity grew rapidly in the wake of Darwin's On the Origin of Species (1859) with the work of Francis Galton and the biometricians. The origin of genetics is usually traced to the 1866 work of the Austrian 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.^[19] Embryology and ecology also became central biological fields, especially as linked to evolution and popularized in the work of Ernst Haeckel.

[edit] Twentieth century biological sciences

At the beginning of the 20th century, biological research was largely a professional endeavour. However, most work was still 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.^[20]

[edit] Classical genetics and evolutionary synthesis

See also: History of genetics and History of model organisms

Thomas Hunt Morgan's illustration of crossing over, part of the Mendelian-chromosome theory of heredity

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).^[21] Soon after, cytologists proposed that chromosomes were the hereditary material. Between 1910 and 1915, Thomas Hunt Morgan and his fly lab forged these two ideas—both controversial—into the "Mendelian-chromosome theory" of heredity. 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.^[22]

Building on his work on heredity and hybridization, Hugo de Vries proposed a mutation theory of evolution, 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—a unification of the idea of evolution by natural selection with Mendelian genetics produced the modern synthesis; inheritance of acquired characters was rejected, while mutationism gave way as genetic theories matured. These ideas continued to be developed in the discipline of population genetics and in the second half of the century began to be applied in the new discipline of the genetics of behavior, sociobiology, and, especially in humans, evolutionary psychology.^[23]

[edit] Ecology, ethology, and environmental science

See also: History of ecology

In the early 20th century, naturalists were faced with increasing pressure to professionalize and 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, and 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; 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.^[24]

The ecological succession concept, pioneered in the 1900s and 1910s by Henry Chandler Cowles and Frederic Clements, was important in early plant ecology. 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 set the pace for the kinds of quantitative methods that spread to 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.^[25]

[edit] Microbiology, biochemistry, and molecular biology

See also: History of molecular biology

By the end of the 19th century all of the major pathways of drug metabolism had been discovered,^{[citation needed]} along with the outlines of protein and fatty acid metabolism and urea synthesis. In the early decades of the twentieth century the role of minor components of foods in human nutrition, the vitamins, began to be isolated and synthesized. In the 1920s and 1930s, biochemists—led by 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.^[26]

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.^[27] 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. Research 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.^[28]

The "central dogma of molecular biology" was proposed by Francis Crick in 1958. This is Crick's reconstruction of how he conceived of the central dogma at the time. The solid lines represent (as it seemed in 1958) known modes of informations transfer, and the dashed lines represent postulated ones.

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. By 1953 James D. Watson and Francis Crick showed that the structure of DNA was a double helix and showed its probable connection to replication. It was clear to many biologists that DNA 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.^[29]

In addition to the Division of Biology at Caltech, the Laboratory of Molecular Biology at Cambridge, and a handful of other institutions, the Pasteur Institute became a major center for molecular biology research in the late 1950s.^[30] François Jacob and Jacques Monod followed the 1959 PaJaMo experiment with a series of experiments and theoretical developments regarding the lac operon that established the concept of gene regulation and identified what came to be known as messenger RNA. By the mid-1960s, the intellectual core of molecular biology—a model for the molecular basis of metabolism and reproduction— was largely complete.^[31]

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 organismal 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.^[32] 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 nascent fields of cybernetics and computer science—became an influential perspective throughout biology.^[33]

In 1965 it was shown that normal cells in culture divide only a fixed number of times (the Hayflick Limit) then aged and died. About the same time, stem cells were shown to be exceptions to this rule and began to be studied in earnest. Toward the end of the century, totipotent stem cells came to be recognized as crucial for the understanding of developmental biology and raised hopes for new medical applications. In 1983 the unity of much of the morphogenesis of organisms from fertilized egg to adult began to be unraveled by the discovery of the homeobox genes, first in fruit flies, then in other insects and animals, including humans.

[edit] Biotechnology, genetic engineering, and genomics

See also: History of biotechnology

While cloning in plants was known for millennia it was only in 1951 that the first animal, the tadpole, was cloned by nuclear transfer. Dolly, the sheep was cloned by transfer of a mature somatic cell nucleus into an enucleated oocyte in 1997. Within a few years, several other animals, including dogs, cats, horses and cattle were cloned by similar methods.

The discovery of the first restriction enzyme was in 1968, and PCR was invented in 1983.

Even the methods of scientific classification of organisms, especially cladistics, began in the last quarter of the century to use RNA and DNA sequences as characters. By the mid 1980s even the overall division of the tree of life into three domains (as opposed to the classical two), the Archaea, the Bacteria, and the Eukarya, based on Woese's pioneering work on 16S rRNA sequencing, became generally accepted in the scientific community.

The largest, most costly single biological study ever undertaken, the Human genome project began in 1988 under the leadership of James Watson, and a first draft of the human DNA sequence was announced in 2000. By 2003 99% of the genome had been sequenced to an accuracy of one part in ten thousand. The HapMap project to determine patterns of differences in the human genome began in 2002 and by 2005 completed its first phase work by of discovering on the order of one million SNPs in 270 people sampled from four distinct populations of people: Han Chinese, Japanese, Yoruba Nigerians, and Northern Europeans. The advent of whole-genome sequencing and surveys of their variation in different populations (races), together with new statistical methods, permitted researchers by 2006 to systematically identify candidate loci for recent natural selection during evolution in humans. Some of these genes were also shown to be ancestry-informative markers which came to be used in genealogical studies and to understand ancient human migrations.

Starting in 1990 an important mechanism of gene regulation, RNA interference began to be understood and became an important laboratory technique to knockdown genes in order to determine their function in model organisms. In 2006 a large international consortium began a collaborative effort to enable researchers to conveniently obtain mice that have any one of its approximately 20000 genes knocked out. This US$100 million effort is the largest biological research endeavor since the human genome project.

The first genome of a plant model organism, Arabidopsis thaliana was sequenced in 2000. Dozens of bacteria, the mouse, the nematode Caenorhabditis elegans and other model organisms were sequenced and their genes mapped, often by large international collaborations. The first decade of the twenty-first century saw the rise of proteomics, computational biology and bioinformatics, with an emphasis on huge databases of experimentally derived data, all connected by the Internet and available to researchers everywhere, which has fundamentally changed the structure of the science of biology itself.

[edit] Notes

[edit] References

[edit] See also

• Timeline of biology and organic chemistry
• Eugenics
• History of agricultural science
• History of anatomy
• History of medicine
• History of zoology (before Darwin)
• History of zoology, post-Darwin
• Molecular structure of Nucleic Acids - article published by James D. Watson and Francis Crick in 1953
• Natural history
• History of phycology

[edit] External links

• The entire Torner Collection of Watercolors c. 1700. Courtesy the Hunt Institute and the Universal Library at Carnegie-Mellon University. Includes Plants, Insects, Fishes, and Mammals from a Mexican Expedition commissioned by Spain.