c. 450 BC – Sushruta wrote the Sushruta Samhita, redacted versions of which, by the third century AD, describe over 120 surgical instruments and 300 surgical procedures, classify human surgery into eight categories, and introduce cosmetic surgery.
c. 380 BC – Diocles wrote the oldest known anatomy book and was the first to use the term anatomy.
c. 350 BC – Aristotle attempted a comprehensive classification of animals. His written works include Historion Animalium, a general biology of animals, De Partibus Animalium, a comparative anatomy and physiology of animals, and De Generatione Animalium, on developmental biology.
?? – Jan Baptist van Helmont performed his famous tree plant experiment in which he shows that the substance of a plant derives from water, a forerunner of the discovery of photosynthesis.
1628 – William Harvey published An Anatomical Exercise on the Motion of the Heart and Blood in Animals
1651 – William Harvey concluded that all animals, including mammals, develop from eggs, and spontaneous generation of any animal from mud or excrement was an impossibility.
In 1661, 1664 and 1665, the blood cells were discerned by Marcello Malpighi. In 1678, the red blood corpuscles was described by Jan Swammerdam of Amsterdam, a Dutch naturalist and physician. The first complete account of the red cells was made by Anthony van Leeuwenhoek of Delft in the last quarter of the 17th century.
1668 – Francesco Redi disproved spontaneous generation by showing that fly maggots only appear on pieces of meat in jars if the jars are open to the air. Jars covered with cheesecloth contained no flies.
1672 – Marcello Malpighi published the first description of chick development, including the formation of muscle somites, circulation, and nervous system.
1677 – Anton van Leeuwenhoek observed spermatozoa.
1683 – Anton van Leeuwenhoek observed bacteria. Leeuwenhoek's discoveries renew the question of spontaneous generation in microorganisms.
1700–1799
1767 – Kaspar Friedrich Wolff argued that the tissues of a developing chick form from nothing and are not simply elaborations of already-present structures in the egg.
1768 – Lazzaro Spallanzani again disproved spontaneous generation by showing that no organisms grow in a rich broth if it is first heated (to kill any organisms) and allowed to cool in a stoppered flask. He also showed that fertilization in mammals requires an egg and semen.
1771 – Joseph Priestley demonstrated that plants produce a gas that animals and flames consume. This gas was oxygen.
1798 – Thomas Malthus discussed human population growth and food production in An Essay on the Principle of Population.
1802 – The term biology in its modern sense was propounded independently by Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur) and Lamarck (Hydrogéologie). The word was coined in 1800 by Karl Friedrich Burdach.
1809 – Lamarck proposed a modern theory of evolution based on the inheritance of acquired characteristics.
1824 – J. L. Prevost and J. B. Dumas showed that the sperm in semen were not parasites, as previously thought, but, instead, the agents of fertilization.
1826 – Karl von Baer showed that the eggs of mammals are in the ovaries, ending a 200-year search for the mammalian egg.
1837 – Theodor Schwann showed that heating air will prevent it from causing putrefaction.
1838 – Matthias Schleiden proposed that all plants are composed of cells.
1839 – Theodor Schwann proposed that all animal tissues are composed of cells. Schwann and Schleinden argued that cells are the elementary particles of life.
1843 – Martin Barry reported the fusion of a sperm and an egg for rabbits in a 1-page paper in the Philosophical Transactions of the Royal Society of London.
1858 – Charles R. Darwin and Alfred Wallace independently proposed a theory of biological evolution ("descent through modification") by means of natural selection. Only in later editions of his works did Darwin used the term "evolution."
1858 – Rudolf Virchow proposed that cells can only arise from pre-existing cells; "Omnis cellula e celulla," all cell from cells. The Cell Theory states that all organisms are composed of cells (Schleiden and Schwann), and cells can only come from other cells (Virchow).
1864 – Louis Pasteur disproved the spontaneous generation of cellular life.
1865 – Gregor Mendel demonstrated in pea plants that inheritance follows definite rules. The Principle of Segregation states that each organism has two genes per trait, which segregate when the organism makes eggs or sperm. The Principle of Independent Assortment states that each gene in a pair is distributed independently during the formation of eggs or sperm. Mendel's trailblazing foundation for the science of genetics went unnoticed, to his lasting disappointment.
1874 – Jacobus van 't Hoff and Joseph-Achille Le Bel advanced a three-dimensional stereochemical representation of organic molecules and propose a tetrahedral carbon atom.
1876 – Oskar Hertwig and Hermann Fol independently described (in sea urchin eggs) the entry of sperm into the egg and the subsequent fusion of the egg and sperm nuclei to form a single new nucleus.
1884 – Emil Fischer began his detailed analysis of the compositions and structures of sugars.
1892 – Hans Driesch separated the individual cells of a 2-cell sea urchin embryo and shows that each cell develops into a complete individual, thus disproving the theory of preformation and showing that each cell is "totipotent," containing all the hereditary information necessary to form an individual.
1922 – Aleksandr Oparin proposed that the Earth's early atmosphere contained methane, ammonia, hydrogen, and water vapor, and that these were the raw materials for the origin of life.
1937 – In Genetics and the Origin of Species, Theodosius Dobzhansky applies the chromosome theory and population genetics to natural populations in the first mature work of neo-Darwinism, also called the modern synthesis, a term coined by Julian Huxley.
1948 – Erwin Chargaff showed that in DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units.
1952 – American developmental biologists Robert Briggs and Thomas King cloned the first vertebrate by transplanting nuclei from leopard frogs embryos into enucleated eggs. More differentiated cells were less able to direct development in the enucleated egg.
1952 – Rosalind Franklin concluded that DNA is a double helix with a diameter of 2nm and the sugar-phosphate backbones on the outside of the helix, based on x ray diffraction studies. She suspected the two sugar-phosphate backbones have a peculiar relationship to each other.
1953 – After examining Franklin's unpublished data, James D. Watson and Francis Crick published a double-helix structure for DNA, with one sugar-phosphate backbone running in the opposite direction to the other. They further suggested a mechanism by which the molecule can replicate itself and serve to transmit genetic information. Their paper, combined with the Hershey-Chase experiment and Chargaff's data on nucleotides, finally persuaded biologists that DNA is the genetic material, not protein.
1955 – Marianne Grunberg-Manago and Severo Ochoa discovered the first nucleic-acid-synthesizing enzyme (polynucleotide phosphorylase), which links nucleotides together into polynucleotides.
1958 – John Gurdon used nuclear transplantation to clone an African Clawed Frog; first cloning of a vertebrate using a nucleus from a fully differentiated adult cell.
1960 – John Kendrew described the structure of myoglobin, the oxygen-carrying protein in muscle.
1960 – Four separate researchers (S. Weiss, J. Hurwitz, Audrey Stevens Niyogi and J. Bonner) discovered bacterial RNA polymerase, which polymerizes nucleotides under the direction of DNA.
1961 – J. Heinrich Matthaei cracked the first codon of the genetic code (the codon for the amino acid phenylalanine) using Grunberg-Manago's 1955 enzyme system for making polynucleotides.
1961 – Joan Oró found that concentrated solutions of ammonium cyanide in water can produce the nucleotide adenine, a discovery that opened the way for theories on the origin of life.
1966 – Genetic code fully cracked through trial-and-error experimental work.
1966 – Kimishige Ishizaka discovered a new type of immunoglobulin, IgE, that develops allergy and explains the mechanisms of allergy at molecular and cellular levels.
1966 – Lynn Margulis proposed the endosymbiotic theory, that the eukaryotic cell is a symbiotic union of primitive prokaryotic cells. Richard Dawkins called the theory "one of the great achievements of twentieth-century evolutionary biology."
1968 – Fred Sanger used radioactive phosphorus as a tracer to chromatographically decipher a 120 base long RNA sequence.
1972 – Stephen Jay Gould and Niles Eldredge proposed an idea they call "punctuated equilibrium", which states that the fossil record is an accurate depiction of the pace of evolution, with long periods of "stasis" (little change) punctuated by brief periods of rapid change and species formation (within a lineage).
1974 – Manfred Eigen and Manfred Sumper showed that mixtures of nucleotide monomers and RNA replicase will give rise to RNA molecules which replicate, mutate, and evolve.
1974 – Leslie Orgel showed that RNA can replicate without RNA-replicase and that zinc aids this replication.
1982 – Stanley B. Prusiner proposed the existence of infectious proteins, or prions. His idea is widely derided in the scientific community, but he wins a Nobel Prize in 1997.
1998 – Mello and Fire publish their work on RNAi in c.elegans, for which they shared the 2006 Nobel Prize in Physiology or Medicine.
1999 – Researchers at the Institute for Human Gene Therapy at the University of Pennsylvania accidentally kill Jesse Gelsinger during a clinical trial of a gene therapy technique, leading the FDA to halt further gene therapy trials at the institute.
