History of biology facts for kids
The history of biology tells the story of how people have studied the living world from ancient times to today. Even though the idea of "biology" as one main subject only came about in the 1800s, the study of living things grew from old traditions in medicine and natural history. These traditions go way back to ancient practices like Ayurveda in India, ancient Egyptian medicine, and the ideas of Aristotle and Galen in ancient Greece and Rome.
During the Middle Ages, Muslim doctors and scholars like Avicenna continued to develop these ancient ideas. Later, during the European Renaissance, people became very interested in observing and experimenting. They discovered many new organisms. Important figures like Vesalius and Harvey used experiments and careful observation to understand how bodies work. Naturalists like Linnaeus and Buffon started to classify the many different kinds of life and study fossils. They also looked at how organisms develop and behave.
Antonie van Leeuwenhoek used microscopy to discover a whole new world of tiny living things called microorganisms. This work helped set the stage for the cell theory. Over the 1700s and 1800s, biology fields like botany (plants) and zoology (animals) became professional sciences. Scientists like Lavoisier began to connect living and non-living things using physics and chemistry. Explorer-naturalists such as Alexander von Humboldt studied how living things interact with their environment and how this changes based on geography. This laid the groundwork for biogeography, ecology, and ethology.
Scientists started to realize that extinction happens and that species can change over time. The cell theory gave a new way to understand the basic building blocks of life. All these discoveries, along with findings from embryology (the study of how living things develop) and paleontology (the study of fossils), came together in Charles Darwin's theory of evolution by natural selection. By the end of the 1800s, people understood that living things don't just appear from nowhere (spontaneous generation), and the germ theory of disease became widely accepted. However, how living things passed on their traits (inheritance) was still a mystery.
In the early 1900s, Gregor Mendel's work on plant heredity was rediscovered. This led to the fast growth of genetics, especially through the work of Thomas Hunt Morgan and his students with fruit flies. By the 1930s, the combination of population genetics and natural selection formed the "neo-Darwinian synthesis" (a modern understanding of evolution). New fields grew quickly, especially after Watson and Crick discovered the structure of DNA. After the "Central Dogma" (how genetic information flows) was established and the genetic code was cracked, biology largely split into two main areas: organismal biology (studying whole organisms) and cellular and molecular biology (studying cells and molecules). By the late 1900s, new fields like genomics and proteomics started to bring these areas back together. Organismal biologists began using molecular tools, and molecular biologists started looking at how genes and the environment interact in natural populations.
Contents
- Early Human Knowledge of Life
- Ancient Civilizations and Early Biology
- Biology in Ancient China and India
- Classical Greek and Roman Biology
- Biology in the Middle Ages
- The Renaissance: A New Look at Life
- The Age of Enlightenment: Classifying and Discovering
- The 1800s: Biology Becomes Specialized
- 20th Century Biology: New Discoveries
- 21st Century Biology: New Frontiers
- See also
Early Human Knowledge of Life
The earliest humans needed to know a lot about plants and animals to survive. They likely shared knowledge about human and animal bodies, and how animals behaved (like where they migrated). A big change in biological knowledge happened about 10,000 years ago with the Neolithic Revolution. Humans began to grow plants for farming and then tamed livestock animals. This allowed societies to settle down in one place.
Ancient Civilizations and Early Biology
Around 3000 to 1200 BCE, the Ancient Egyptians and Mesopotamians made important discoveries in astronomy, mathematics, and medicine. These ideas later influenced Greek natural philosophy, which greatly shaped what we now call biology.
Ancient Egypt's Contributions
More than a dozen medical papyri (ancient Egyptian writings on medicine) have been found. The Edwin Smith Papyrus (around 1600 BCE) is the oldest surviving guide to surgery. The Ebers Papyrus (also around 1600 BCE) is a guide for preparing and using medicines for different illnesses.
Ancient Egypt is also famous for developing embalming, which was used for mummification. This process helped preserve human bodies and stop them from decaying.
Mesopotamian Insights into Life
The people of Mesopotamia were more interested in how the gods organized the universe than in the natural world itself. They studied animal bodies for divination (predicting the future), especially the liver, which they saw as important for telling fortunes. Animal behavior was also studied for this purpose. Most knowledge about training animals was probably passed down by word of mouth, but one text about training horses has survived.
Ancient Mesopotamians didn't separate "science" from magic. When someone got sick, doctors would prescribe both magical sayings and medicines. The first medical prescriptions were written in Sumerian around 2112–2004 BCE. The most detailed Babylonian medical text was the Diagnostic Handbook, written by the chief scholar Esagil-kin-apli around 1069–1046 BCE. In these cultures, the main medical expert was an exorcist-healer called an āšipu. This job was passed from father to son and was highly respected. Less common was the asu, a healer who treated physical problems with herbs, animal products, and minerals, as well as potions and ointments. These doctors, who could be male or female, also treated wounds, set broken bones, and did simple surgeries. The ancient Mesopotamians also practiced prophylaxis (preventive measures) to stop diseases from spreading.
Biology in Ancient China and India
Ideas about nature and health also developed separately in places like China and India, different from Western traditions. In ancient China, early biological ideas were found in the work of herbologists, doctors, alchemists, and philosophers. For example, the Taoist tradition of Chinese alchemy focused on health, aiming for the elixir of life. Traditional Chinese medicine often used the ideas of yin and yang and the five phases. Taoist philosophers, like Zhuangzi in the 4th century BCE, even had ideas similar to evolution, suggesting that species were not fixed and changed based on their environment.
One of the oldest organized medical systems is Ayurveda from ancient India. It started around 1500 BCE from the Atharvaveda, one of the oldest Indian books of knowledge.
The ancient Indian Ayurveda tradition developed the idea of three "humours" (body fluids), similar to the four humours of ancient Greek medicine. However, the Ayurvedic system was more complex, including ideas about the body being made of five elements and seven basic tissues. Ayurvedic writers also sorted living things into four groups based on how they were born (from the womb, eggs, heat & moisture, and seeds). They also described how a fetus develops in detail. They made big advances in surgery, often without cutting open human bodies (dissection) or living animals (vivisection). One of the earliest Ayurvedic books was the Sushruta Samhita, written by Sushruta in the 6th century BCE. It was also an early guide to medicines, describing 700 medicinal plants, 64 preparations from minerals, and 57 from animal sources.
Classical Greek and Roman Biology
The early Greek philosophers asked many questions about life. But they didn't create much organized biological knowledge. However, the medical ideas of Hippocrates and his followers, especially humorism (the idea of body fluids), had a lasting impact.
The philosopher Aristotle was the most important scholar of the living world from classical antiquity. While his early work was more about ideas, Aristotle's later biological writings focused on observing and understanding why things happen in nature. He made countless observations of nature, especially the habits and features of plants and animals around him. He spent a lot of time categorizing them. In total, Aristotle classified 540 animal species and cut open at least 50. He believed that all natural processes were guided by intellectual purposes.
Aristotle, and almost all Western scholars after him until the 1700s, believed that creatures were arranged in a perfect ladder from plants up to humans. This was called the scala naturae or Great Chain of Being. Aristotle's student, Theophrastus, wrote several books on botany, including the History of Plants. This book was the most important ancient contribution to botany and was used even into the Middle Ages. Many of Theophrastus's names are still used today, like carpos for fruit. Dioscorides wrote an important and encyclopedic guide to medicines, De Materia Medica. It described about 600 plants and how they were used in medicine. Pliny the Elder, in his Natural History, also collected a huge amount of information about nature, including many plants and animals.
Some scholars in the Hellenistic period (under the Ptolemies)—especially Herophilus and Erasistratus—improved on Aristotle's work on how bodies function. They even performed dissections and vivisections (cutting open living things). Claudius Galen became the most important expert on medicine and anatomy. Although some ancient atomists like Lucretius disagreed with the idea that all life is designed for a purpose, this idea (and later natural theology after Christianity grew) remained central to biological thought until the 1700s and 1800s. The ideas from Greek natural history and medicine survived, but they were generally accepted without question in medieval Europe.
Biology in the Middle Ages
When the Roman Empire declined, much knowledge was lost or destroyed. However, doctors still used many Greek traditions in their training and practice. In Byzantium and the Islamic world, many Greek works were translated into Arabic, and many of Aristotle's books were saved.
During the High Middle Ages, a few European scholars like Hildegard of Bingen, Albertus Magnus, and Frederick II wrote about natural history. The growth of European universities was important for physics and philosophy, but it didn't have much impact on the study of biology.
The Renaissance: A New Look at Life
The European Renaissance brought a greater interest in both observing nature and studying how bodies work. In 1543, Andreas Vesalius started the modern era of Western medicine with his important book on human anatomy, De humani corporis fabrica. This book was based on cutting open dead bodies. Vesalius was the first of many anatomists who slowly replaced old ways of thinking with empiricism (learning from experience and observation) in physiology and medicine. They relied on what they saw firsthand rather than just old texts. Through herbalism (the study of medicinal plants), medicine also indirectly led to new observations in plant study. Otto Brunfels, Hieronymus Bock, and Leonhart Fuchs wrote a lot about wild plants, starting a new way of looking at all plant life. Books about animals (Bestiaries) also became more detailed, especially with the work of William Turner, Pierre Belon, Guillaume Rondelet, Conrad Gessner, and Ulisse Aldrovandi.
Artists like Albrecht Dürer and Leonardo da Vinci, who often worked with naturalists, were also interested in human and animal bodies. They studied how bodies work in detail and helped increase anatomical knowledge. The traditions of alchemy and natural magic, especially in the work of Paracelsus, also claimed to have knowledge of the living world. Alchemists analyzed organic matter chemically and experimented a lot with both biological and mineral medicines. This was part of a bigger change in how people viewed the world, as the old idea of nature as an organism was replaced by the idea of nature as a machine. This change continued into the 1600s.
The Age of Enlightenment: Classifying and Discovering
Organizing, naming, and classifying living things were very important in natural history during the 1600s and 1700s. Carl Linnaeus published a basic system for classifying the natural world in 1735. In the 1750s, he introduced scientific names (like Homo sapiens for humans) for all his species. Linnaeus thought of species as unchanging parts of a designed system. But the other great naturalist of the 1700s, Buffon, saw species as artificial groups and living forms as changeable. He even suggested that different species might have come from a common ancestor. Even though he didn't believe in evolution, Buffon was a key figure in the history of evolutionary thought; his work influenced the evolutionary ideas of both Lamarck and Darwin.
Discovering and describing new species, and collecting specimens, became a popular hobby for scientists and a profitable business for others. Many naturalists traveled the world looking for scientific knowledge and adventure.
Building on Vesalius's work, William Harvey and other natural philosophers experimented on living bodies (both human and animal). They investigated the roles of blood, veins, and arteries. Harvey's book De motu cordis in 1628 began the end of Galen's old theories. Along with Santorio Santorio's studies of metabolism, it was an important example of using numbers and measurements to study how bodies work.
In the early 1600s, the tiny world of biology was just starting to be explored. Some lens makers and natural philosophers had made simple microscopes since the late 1500s. Robert Hooke published his important book Micrographia in 1665, based on observations with his own microscope. But it wasn't until Antonie van Leeuwenhoek greatly improved lens making in the 1670s—making lenses that could magnify up to 200 times—that scholars discovered spermatozoa, bacteria, infusoria, and the amazing variety of microscopic life. Similar studies by Jan Swammerdam led to a new interest in entomology (the study of insects) and developed basic techniques for microscopic dissection and staining.
As the microscopic world grew, the macroscopic world (the world we can see) seemed to shrink. Botanists like John Ray worked to fit the huge number of newly discovered organisms from around the world into a clear classification system and a clear theology (natural theology). Debates about another flood, the Biblical flood, helped the development of paleontology. In 1669, Nicholas Steno published an essay explaining how the remains of living organisms could be trapped in layers of sediment and turn into fossils. Although Steno's ideas about fossils were well known, not all naturalists accepted that all fossils came from living things until the late 1700s. This was due to philosophical and religious debates about things like the age of the earth and extinction.
The 1800s: Biology Becomes Specialized
Up until the 1800s, biology was mostly divided into medicine (which studied how bodies are built and how they work) and natural history (which looked at the variety of life and how living things interact with each other and with non-living things). By 1900, many of these areas overlapped. Natural history had largely been replaced by more specialized scientific fields like cytology (cells), bacteriology (bacteria), morphology (form and structure), embryology (development), geography, and geology.
The Word "Biology" Appears
The word biology as we use it today seems to have been introduced by different people around the same time: Thomas Beddoes (1799), Karl Friedrich Burdach (1800), Gottfried Reinhold Treviranus (1802), and Jean-Baptiste Lamarck (1802). The word itself comes from the Greek words bíos (life) and logia (branch of study).
Before biology, people used other terms to describe the study of animals and plants. Natural history referred to describing living things, but it also included things like mineralogy. From the Middle Ages through the Renaissance, the main way to organize natural history was the scala naturae or Great Chain of Being. Natural philosophy and natural theology covered the ideas and deeper meanings of plant and animal life, dealing with questions about why organisms exist and behave as they do. These subjects also included what we now call geology, physics, chemistry, and astronomy. Physiology and plant medicine were part of medicine. Botany, Zoology, and Geology (for fossils) replaced natural history and natural philosophy in the 1700s and 1800s before biology became widely used. Even today, "botany" and "zoology" are still common terms, though they are now part of the larger field of biology.
Natural History and Natural Philosophy Merge
Extensive travel by naturalists in the early to mid-1800s brought a lot of new information about the variety and spread of living organisms. The work of Alexander von Humboldt was especially important. He studied the relationship between organisms and their environment (natural history) using the scientific methods of natural philosophy (physics and chemistry). Humboldt's work laid the groundwork for biogeography and inspired many scientists for generations.
Geology and Paleontology: Uncovering Earth's Past
The new field of geology also brought natural history and natural philosophy closer. The creation of the stratigraphic column (layers of rock) connected where organisms lived in space to when they lived in time. This was a key step before the idea of evolution. Georges Cuvier and others made big advances in comparative anatomy (comparing body structures) and paleontology in the late 1790s and early 1800s. By comparing living mammals with fossil remains, Cuvier showed that fossils were the remains of species that had become extinct. Before this, many believed that these species still existed somewhere else in the world. Fossils found by Gideon Mantell, William Buckland, Mary Anning, and Richard Owen helped show that there was an 'age of reptiles' before the prehistoric mammals. These discoveries fascinated the public and drew attention to the history of life on Earth. Most of these geologists believed in catastrophism (that Earth's features were formed by sudden, violent events). But Charles Lyell's influential book Principles of Geology (1830) made Hutton's uniformitarianism popular. This theory explained the past and present of geology using the same ongoing processes.
Evolution and Biogeography: Life's Changing Story
The most important evolutionary theory before Darwin's was by Jean-Baptiste Lamarck. Based on the inheritance of acquired characteristics (the idea that traits gained during an organism's life could be passed on), it described a chain of development from the smallest microbe to humans. The British naturalist Charles Darwin, combining Humboldt's biogeography, Lyell's uniformitarian geology, Thomas Malthus's ideas on population growth, and his own knowledge of body structures, created a more successful evolutionary theory based on natural selection. Similar evidence led Alfred Russel Wallace to reach the same conclusions independently.
The 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 in 1859 is often seen as the most important event in the history of modern biology. Darwin's reputation as a naturalist, the serious tone of his work, and especially the huge amount of strong evidence he presented, allowed Origin to succeed where earlier evolutionary books had failed. Most scientists were convinced of evolution and common descent by the end of the 1800s. However, natural selection was not fully accepted as the main way evolution happened until the 1900s, because most ideas about heredity at the time didn't seem to fit with the idea of random changes being inherited.
Wallace, building on earlier work by de Candolle, Humboldt, and Darwin, made big contributions to zoogeography (the study of animal distribution). Because he was interested in how species change, he paid special attention to where similar species were found during his fieldwork in South America and the Malay archipelago. In the archipelago, he identified the Wallace line, which divides the animals of the islands into an Asian zone and a New Guinea/Australian zone. His main question—why the animals on islands with such similar climates were so different—could only be answered by thinking about their origins. In 1876, he wrote The Geographical Distribution of Animals, which was the main reference for over fifty years. He then wrote Island Life in 1880, focusing on island biogeography. He expanded the six-zone system developed by Philip Sclater for birds to all kinds of animals. His way of organizing data on animal groups in different zones showed the clear differences. His understanding of evolution allowed him to give logical explanations, which hadn't been done before.
The scientific study of heredity (how traits are passed down) grew quickly after Darwin's Origin of Species, with the work of Francis Galton and the biometricians. The start of genetics is usually traced to the 1866 work of the monk Gregor Mendel, who later received credit for the laws of inheritance. However, his work wasn't recognized as important until 35 years later. In the meantime, many theories of inheritance were debated and studied. Embryology and ecology also became central biological fields, especially as they connected to evolution and were made popular by the work of Ernst Haeckel. Most of the 1800s work on heredity, however, was not about natural history but about experimental physiology.
Physiology: How Bodies Work
During the 1800s, the study of physiology grew a lot. It changed from being mainly about medicine to a wide-ranging study of the physical and chemical processes of life. This included plants, animals, and even microorganisms, not just humans. The idea of living things as machines became a very popular way of thinking in biology.
Cell Theory, Embryology, and Germ Theory
Advances in microscopy also had a big impact on biological thinking. In the early 1800s, several biologists pointed out the central importance of the cell. In 1838 and 1839, Schleiden and Schwann started promoting the ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life. However, they didn't agree with the idea that (3) all cells come from other cells dividing. Thanks to the work of Robert Remak and Rudolf Virchow, by the 1860s most biologists accepted all three parts of what became known as cell theory.
Cell theory led biologists to see individual organisms as groups of interdependent cells. Scientists in the growing field of cytology, using increasingly powerful microscopes and new staining methods, soon found that even single cells were much more complex than the simple fluid-filled chambers described by earlier microscopists. Robert Brown had described the nucleus in 1831. By the end of the 1800s, cytologists identified many key cell parts: chromosomes, centrosomes, mitochondria, chloroplasts, and other structures made visible through staining. Between 1874 and 1884, Walther Flemming described the stages of mitosis (cell division). He showed that these stages were real processes in living cells, not just effects of staining. He also showed that chromosomes doubled in number just before a cell divided to produce a new cell. Much of the research on cell reproduction came together in August Weismann's theory of heredity. He identified the nucleus (especially chromosomes) as the material that carries traits. He also suggested the difference between somatic cells (body cells) and germ cells (reproductive cells), arguing that the number of chromosomes must be halved for germ cells (a step towards understanding meiosis). Weismann's ideas were very influential, especially in the new field of experimental embryology.
By the mid-1850s, the miasma theory of disease (that diseases came from bad air) was largely replaced by the germ theory of disease. This created a lot of interest in microorganisms and how they interact with other forms of life. By the 1880s, bacteriology became a clear field, especially through the work of Robert Koch. He introduced methods for growing pure cultures of bacteria on agar gels in Petri dishes. The long-held idea that living organisms could easily appear from non-living matter (spontaneous generation) was disproven by experiments done by Louis Pasteur. Meanwhile, debates about vitalism (life has a special force) versus mechanism (life can be explained by physical and chemical laws) continued.
Organic Chemistry and Experimental Physiology
In chemistry, a main question was the difference between organic and inorganic substances, especially in processes like fermentation and putrefaction (decay). Since Aristotle, these had been seen as purely biological processes. However, Friedrich Wöhler, Justus Liebig, and other pioneers of the growing field of organic chemistry—building on Lavoisier's work—showed that the organic world could often be studied using physical and chemical methods. In 1828, Wöhler showed that the organic substance urea could be created by chemical means without involving life, which strongly challenged vitalism. Cell extracts ("ferments") that could cause chemical changes were discovered, starting with diastase in 1833. By the end of the 1800s, the idea of enzymes was well established.
Physiologists like Claude Bernard explored (through experiments, including vivisection) the chemical and physical functions of living bodies in great detail. This laid the groundwork for endocrinology (the study of hormones, which grew quickly after the discovery of the first hormone, secretin, in 1902), biomechanics, and the study of nutrition and digestion. The importance and variety of experimental physiology methods, in both medicine and biology, grew dramatically in the second half of the 1800s. Controlling and manipulating life processes became a main goal, and experiments became central to biological education.
20th Century Biology: New Discoveries
At the start of the 1900s, biological research was mostly done by professionals. Much of the work still followed the natural history style, focusing on describing forms and evolutionary relationships rather than experiments to find causes. However, experimental physiologists and embryologists, especially in Europe, who were against vitalism, became more influential. The huge success of experimental approaches to development, heredity, and metabolism in the early 1900s showed how powerful experiments could be in biology. In the following decades, experimental work replaced natural history as the main way to do research.
Ecology and Environmental Science
In the early 1900s, naturalists faced pressure to make their methods more scientific and experimental, like the new laboratory-based biology fields. Ecology emerged as a mix of biogeography and the idea of biogeochemical cycles (how chemicals move through ecosystems) pioneered by chemists. Field biologists developed quantitative methods like the quadrat (a square frame for sampling) and adapted lab instruments and cameras for fieldwork to make their work different from traditional natural history. Zoologists and botanists tried to reduce the unpredictability of the living world by doing lab experiments and studying semi-controlled natural environments like gardens. New places like the Carnegie Station for Experimental Evolution and the Marine Biological Laboratory provided more controlled environments for studying organisms throughout their entire life cycles.
The idea of ecological succession (how ecosystems change over time), developed in the early 1900s 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 lakes and rivers (limnology), and Charles Elton's studies of animal food chains were pioneers among the many quantitative methods that appeared in the developing ecological fields. Ecology became an independent subject in the 1940s and 1950s after Eugene P. Odum brought together many ideas of ecosystem ecology, focusing on relationships between groups of organisms (especially how materials and energy move).
In the 1960s, as evolutionary thinkers explored the possibility of different units of selection, ecologists started using evolutionary approaches. In population ecology, the debate over group selection was short but intense; by 1970, most biologists agreed that natural selection rarely worked above the level of individual organisms. However, the evolution of ecosystems became a lasting research focus. Ecology grew rapidly with the rise of the environmental movement. The International Biological Program tried to apply the methods of big science (which had been so successful in physics) to ecosystem ecology and urgent environmental issues. Smaller, independent efforts like island biogeography and the Hubbard Brook Experimental Forest helped redefine the scope of this increasingly diverse field.
Genetics, Evolution, and the Modern Synthesis
The year 1900 saw the "rediscovery of Mendel" by Carl Correns, who arrived at Mendel's laws (which weren't exactly stated in Mendel's original work). Soon after, cytologists (cell biologists) suggested that chromosomes were the material that carried traits. This idea was developed by Carl Correns and others between 1910 and 1915 as the "Mendelian-chromosome theory" of heredity. Thomas Hunt Morgan and the "Drosophilists" in his fly lab applied this to a new model organism. They proposed crossing over to explain why some traits were linked together and created genetic maps of the fruit fly Drosophila melanogaster, which became a widely used model organism.
Hugo de Vries tried to connect the new genetics with evolution. Based on his work with heredity and hybridization, he proposed a theory of mutationism, which was widely accepted in the early 1900s. Lamarckism, or the theory of inheritance of acquired characteristics, also had many supporters. Darwinism seemed incompatible with the continuously changing traits studied by biometricians, which appeared only partly inheritable. In the 1920s and 1930s—after the Mendelian-chromosome theory was accepted—the new field of population genetics, with the work of R.A. Fisher, J.B.S. Haldane, and Sewall Wright, combined the idea of evolution by natural selection with Mendelian genetics. This created the modern synthesis. The idea of inheriting acquired characteristics was rejected, while mutationism faded as genetic theories became more advanced.
In the second half of the century, the ideas of population genetics began to be used in the new fields of behavioral genetics, sociobiology, and, especially for humans, evolutionary psychology. In the 1960s, W.D. Hamilton and others used game theory to explain altruism (selfless behavior) from an evolutionary perspective through kin selection (helping relatives). The possible origin of higher organisms through endosymbiosis (where one organism lives inside another), and different ways of looking at molecular evolution (the gene-centered view, which saw selection as the main cause of evolution, and the neutral theory, which made genetic drift a key factor) led to ongoing debates about the right balance of adaptationism and chance in evolutionary theory.
In the 1970s, Stephen Jay Gould and Niles Eldredge proposed the theory of punctuated equilibrium. This theory suggests that long periods of little change are the most common feature in the fossil record, and that most evolutionary changes happen quickly over relatively short periods. In 1980, Luis Alvarez and Walter Alvarez suggested that an impact event (like an asteroid hitting Earth) caused the Cretaceous–Paleogene extinction event (the extinction of the dinosaurs). Also in the early 1980s, statistical analysis of marine organism fossils by Jack Sepkoski and David M. Raup led to a better understanding of how important mass extinction events are to the history of life on Earth.
Biochemistry, Microbiology, and Molecular Biology
By the end of the 1800s, all the major ways that drugs are processed in the body had been discovered, along with the basics of how proteins and fatty acids are used, and how urea is made. In the early 1900s, the small but important parts of human nutrition, the vitamins, began to be isolated and created in labs. Better lab techniques like chromatography and electrophoresis led to fast advances in physiological chemistry. This field, now called biochemistry, started to become independent from its medical origins. In the 1920s and 1930s, biochemists—led by Hans Krebs and Carl and Gerty Cori—began to figure out many of the central metabolic pathways of life: the citric acid cycle, glycogenesis and glycolysis (how sugar is stored and broken down), and the creation of steroids and porphyrins. Between the 1930s and 1950s, Fritz Lipmann and others established the role of ATP as the universal energy carrier in the cell, and mitochondria as the "powerhouse" of the cell. This kind of biochemical work continued to be very active throughout the 1900s and into the 2000s.
The Start of Molecular Biology
After classical genetics grew, many biologists—including a new group of physicists who moved into biology—looked into the question of what a gene is and what it's made of. Warren Weaver, who led the science division of the Rockefeller Foundation, gave grants to support research that used physics and chemistry methods to solve basic biological problems. He even created the term molecular biology for this approach in 1938. Many important biological breakthroughs of the 1930s and 1940s were funded by the Rockefeller Foundation.
Like biochemistry, the overlapping fields of bacteriology and virology (later combined as microbiology), which were between science and medicine, grew quickly in the early 1900s. Félix d'Herelle's isolation of bacteriophage (viruses that infect bacteria) during World War I started a long line of research focused on these viruses and the bacteria they infect.
Developing standard, genetically identical organisms that could produce repeatable experimental results was essential for the growth of molecular genetics. After early work with Drosophila (fruit flies) and maize (corn), using simpler model systems like the bread mold Neurospora crassa made it possible to connect genetics to biochemistry. The most important example was Beadle and Tatum's one gene-one enzyme hypothesis in 1941. Genetics experiments on even simpler systems like tobacco mosaic virus and bacteriophage, helped by new technologies like electron microscopy and ultracentrifugation, forced scientists to rethink the literal meaning of life. Virus heredity and reproducing nucleoprotein cell structures outside the nucleus ("plasmagenes") made the accepted Mendelian-chromosome theory more complicated.
Oswald Avery showed in 1943 that DNA was likely the genetic material of the chromosome, not its protein. This was definitively proven by the 1952 Hershey–Chase experiment—one of many contributions from the "phage group" led by physicist-turned-biologist Max Delbrück. In 1953, James 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 subtly noted, "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." After the 1958 Meselson–Stahl experiment confirmed that DNA copies itself in a semi-conservative way, it was clear to most biologists that the sequence of nucleic acids must somehow determine the amino acid sequence in proteins. Physicist George Gamow proposed that a fixed genetic code connected proteins and DNA. Between 1953 and 1961, few biological sequences (either DNA or protein) were known, but many code systems were proposed. This situation became even more complicated with growing knowledge of the intermediate role of RNA. In 1961, it was shown that when a gene codes for a protein, three sequential bases of a gene’s DNA specify each amino acid of the protein. So, the genetic code is a triplet code, where each triplet (called a codon) specifies a particular amino acid. Also, it was shown that the codons do not overlap in the DNA sequence that codes for a protein, and each sequence is read from a fixed starting point. To actually figure out the code, a lot of experiments in biochemistry and bacterial genetics were done between 1961 and 1966—most importantly the work of Nirenberg and Khorana. During 1962-1964, many conditional lethal mutants of a bacterial virus were found. These mutants were used in different labs to improve the basic understanding of how the proteins involved in DNA replication, DNA repair, DNA recombination, and the assembly of molecular structures work and interact.
Molecular Biology Grows
Besides the Division of Biology at Caltech, the Laboratory of Molecular Biology (and its earlier forms) at Cambridge, and a few other places, the Pasteur Institute became a major center for molecular biology research in the late 1950s. Scientists at Cambridge, led by Max Perutz and John Kendrew, focused on the fast-growing field of structural biology. They combined X-ray crystallography with Molecular modelling and the new possibilities of digital computing. A number of biochemists led by Frederick Sanger later joined the Cambridge lab, bringing together the study of large molecule structure and function. At the Pasteur Institute, François Jacob and Jacques Monod followed the 1959 PaJaMo experiment with a series of publications about the lac operon. This work established the idea of gene regulation and identified what became known as messenger RNA. By the mid-1960s, the main ideas of molecular biology—a model for how metabolism and reproduction work at the molecular level—were largely complete.
The late 1950s to the early 1970s was a time of intense research and growth for molecular biology, which had only recently become a somewhat unified field. In what organismal biologist E. O. Wilson called "The Molecular Wars," the methods and people of molecular biology spread quickly, often coming to dominate departments and even entire fields. Molecularization was especially important in genetics, immunology, embryology, and neurobiology. The idea that life is controlled by a "genetic program"—a metaphor Jacob and Monod introduced from the new fields of cybernetics and computer science—became a very influential idea throughout biology. Immunology, in particular, became linked with molecular biology, with new ideas flowing both ways: the clonal selection theory developed by Niels Jerne and Frank Macfarlane Burnet in the mid-1950s helped explain the general ways proteins are made.
Resistance to the growing influence of molecular biology was especially clear in evolutionary biology. Protein sequencing had great potential for studying evolution quantitatively (through the molecular clock hypothesis). But leading evolutionary biologists questioned how relevant molecular biology was for answering the big questions about what causes evolution. Departments and fields split as organismal biologists insisted on their importance and independence. Theodosius Dobzhansky famously stated 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 universal cause of evolution, at least at the molecular level. It proposed that molecular evolution might be a fundamentally different process from morphological evolution. (Solving this "molecular/morphological paradox" has been a main focus of molecular evolution research since the 1960s.)
Biotechnology, Genetic Engineering, and Genomics
Biotechnology in a general sense has been an important part of biology since the late 1800s. With the industrialization of brewing and agriculture, chemists and biologists realized the great potential of human-controlled biological processes. In particular, fermentation was a big help 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 many hybrid high-yield crops and agricultural technologies, which formed the basis for the Green Revolution.
Recombinant DNA: Changing Genes
Biotechnology in the modern sense of genetic engineering began in the 1970s, with the invention of recombinant DNA techniques. Restriction enzymes were discovered and described in the late 1960s, following the isolation, duplication, and then synthesis of viral genes. Starting with the lab of Paul Berg in 1972 (helped by EcoRI from Herbert Boyer's lab, building on work with ligase by Arthur Kornberg's lab), molecular biologists put these pieces together to create the first transgenic organisms (organisms with genes from another species). Soon after, others started using plasmid vectors and adding genes for antibiotic resistance, greatly increasing what recombinant techniques could do.
Scientists and many people outside of science reacted to these developments with both excitement and caution, worried about potential dangers (especially the possibility of a fast-growing bacteria with a virus that causes cancer). Leading molecular biologists, led by Berg, suggested a temporary pause on recombinant DNA research until the dangers could be assessed and rules could be created. This pause was largely followed until the participants in the 1975 Asilomar Conference on Recombinant DNA made policy recommendations and concluded that the technology could be used safely.
After Asilomar, new genetic engineering techniques and uses developed rapidly. DNA sequencing methods improved greatly (pioneered by Frederick Sanger and Walter Gilbert), as did oligonucleotide synthesis and transfection techniques (methods to introduce DNA into cells). Researchers learned to control the expression of transgenes (genes transferred from one organism to another). They soon raced—in both academic and industrial settings—to create organisms that could produce human hormones by expressing human genes. However, this was a harder task than molecular biologists had expected. Developments between 1977 and 1980 showed that, because of split genes and splicing, higher organisms had a much more complex system of gene expression than the bacteria models used in earlier studies. The first such race, for making 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 connection between biology, industry, and law.
Molecular Systematics and Genomics
By the 1980s, protein sequencing had already changed how organisms were classified (especially cladistics, which groups organisms by shared ancestry). But biologists soon began to use RNA and DNA sequences as characteristics. This increased the importance of molecular evolution within evolutionary biology, as the results of molecular systematics (classification based on molecules) could be compared with traditional evolutionary trees based on body structure. Following the pioneering ideas of Lynn Margulis on endosymbiotic theory, which says that some organelles (parts of cells) in eukaryotic cells came from free-living prokaryotic organisms through symbiotic relationships, even the overall division of the tree of life was changed. 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.
The development and popularity of the polymerase chain reaction (PCR) in the mid-1980s (by Kary Mullis and others) was another turning point in modern biotechnology. It greatly increased the ease and speed of genetic analysis. Combined 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. It also opened the possibility of sequencing entire genomes.
The unity of much of the morphogenesis (how organisms develop their shape) from fertilized egg to adult began to be understood after the discovery of the homeobox genes. These were first found in fruit flies, then in other insects and animals, including humans. These developments led to advances in the field of evolutionary developmental biology. This field helps us understand how the different body plans of animal groups have evolved and how they are related to each other.
The Human Genome Project—the largest and most expensive single biological study ever—began in 1988 under the leadership of James D. Watson. This followed preliminary work with genetically simpler model organisms like E. coli, S. cerevisiae (yeast), and C. elegans (a worm). Shotgun sequencing and gene discovery methods pioneered by Craig Venter—and driven by the financial promise of gene patents with Celera Genomics—led to a public-private sequencing competition that ended in a compromise with the first draft of the human DNA sequence announced in 2000.
21st Century Biology: New Frontiers
At the start of the 21st century, biological sciences merged with previously separate new and classic fields like Physics into research areas like Biophysics. Advances were made in analytical chemistry and physics tools, including better sensors, optics, tracers, instruments, signal processing, networks, robots, satellites, and computer power for collecting, storing, analyzing, modeling, visualizing, and simulating data. These technological advances allowed for theoretical and experimental research, including publishing molecular biochemistry, biological systems, and ecosystem science on the internet. This gave worldwide access to better measurements, theoretical models, complex simulations, theory-predictive model experiments, analysis, worldwide internet observational data reporting, open peer-review, collaboration, and internet publication. New fields of biological sciences research emerged, including Bioinformatics, Neuroscience, Theoretical biology, Computational genomics, Astrobiology, and Synthetic Biology.
See also
In Spanish: Historia de la biología para niños
- History of botany
- Outline of biology
- Timeline of biology and organic chemistry
