* 1900 – Hugo de Vries, Carl Correns and Erich von Tschermak independently rediscovered Mendel's paper on heredity.
* 1902 – Walter Sutton and Theodor Boveri, independently proposed that the chromosomes carry the hereditary information.
* 1905 – William Bateson coined the term "genetics" to describe the study of biological inheritance.
* 1906 – Mikhail Tsvet discovered the chromatography technique for organic compound separation.
* 1907 – Ivan Pavlov demonstrated conditioned responses with salivating dogs.
* 1907 – Hermann Emil Fischer artificially synthesized peptide amino acid chains and thereby shows that amino acids in proteins are connected by amino group-acid group bonds.
* 1909 – Wilhelm Johannsen coined the word "gene."
* 1911 – Thomas Hunt Morgan proposed that genes are arranged in a line on the chromosomes.
* 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.
* 1926 – James B. Sumner showed that the urease enzyme is a protein.
* 1928 – Otto Diels and Kurt Alder discovered the Diels-Alder cycloaddition reaction for forming ring molecules.
* 1928 – Alexander Fleming discovered the first antibiotic, penicillin
* 1929 – Phoebus Levene discovered the sugar deoxyribose in nucleic acids.
* 1929 – Edward Doisy and Adolf Butenandt independently discovered estrone.
* 1930 – John Howard Northrop showed that the pepsin enzyme is a protein.
* 1931 – Adolf Butenandt discovered androsterone.
* 1932 – Hans Adolf Krebs discovered the urea cycle.
* 1933 – Tadeus Reichstein artificially synthesized vitamin C; first vitamin synthesis.
* 1935 – Rudolf Schoenheimer used deuterium as a tracer to examine the fat storage system of rats.
* 1935 – Wendell Stanley crystallized the tobacco mosaic virus.
* 1935 – Konrad Lorenz described the imprinting behavior of young birds.
* 1937 – Dorothy Crowfoot Hodgkin discovered the three-dimensional structure of cholesterol.
* 1937 – Hans Adolf Krebs discovered the tricarboxylic acid cycle.
* 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.
* 1938 – Marjorie Courtenay-Latimer discovered a living coelacanth off the coast of southern Africa.
* 1940 – Donald Griffin and Robert Galambos announced their discovery of echolocation by bats.
* 1942 – Max Delbrück and Salvador Luria demonstrated that bacterial resistance to virus infection is caused by random mutation and not adaptive change.
* 1944 – Oswald Avery shows that DNA carried the hereditary information in pneumococcus bacteria.
* 1944 – Robert Burns Woodward and William von Eggers Doering synthesized quinine.
* 1945 – Dorothy Crowfoot Hodgkin discovered the three-dimensional structure of penicillin.
* 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.