The idea that life changes
Until the 18th century many people believed species were created as they are now. In 1809 Jean-Baptiste Lamarck set out a systematic theory of evolution, though his explanation — that organs strengthened by use are passed to offspring — was later largely rejected. In 1858 Charles Darwin and Alfred Russel Wallace jointly presented their independently developed ideas, and in On the Origin of Species (1859) Darwin explained evolution by natural selection: among the variation between individuals, traits that help survival and reproduction are passed on more often. Darwin saw all life as connected in a single tree of life.
Meeting genetics
Darwin did not know how traits were inherited, but in 1866 Gregor Mendel published the laws of inheritance from pea experiments. After Mendel was rediscovered in 1900, Fisher, Haldane, Wright, Dobzhansky and others in the 1930s–40s combined selection and genes into the "modern synthesis". When the structure of DNA was solved in 1953, evolution could be studied at the molecular level, and in 1968 Japan's Motoo Kimura proposed the neutral theory — that much molecular change results from chance spread of mutations that are neither helpful nor harmful. In 1972 Eldredge and Gould proposed punctuated equilibrium, with long stasis interrupted by relatively rapid change, sparking debate about evolution's tempo. Besides selection, evolution also happens through random genetic drift and gene flow between populations.
Evidence and common myths
The evidence is many-stranded. Fossils show transitional forms such as Archaeopteryx and Tiktaalik, and the line from dinosaurs to birds, as well as new groups flourishing after mass extinctions. Comparing DNA shows that closer species have more similar sequences. Evolution is observed today: Peter and Rosemary Grant recorded Galápagos finch beaks changing within a few generations with drought and competition, and Richard Lenski's E. coli experiment, begun in 1988, has tracked change over tens of thousands of generations; bacterial antibiotic resistance is evolution before our eyes. Contrary to a common myth, humans did not descend from today's monkeys but share common ancestors with chimpanzees and others. Evolution is not a ladder towards "better" or a fixed goal but more like a branching tree shaped by environment, and populations, not individuals, evolve. As Dobzhansky wrote in 1973, "Nothing in biology makes sense except in the light of evolution."
FAQ
- Is evolution "just a theory"?
- In science a theory is an explanatory framework supported by extensive evidence. That evolution has occurred and that life shares common ancestry are broadly accepted in biology, while details of mechanisms are still researched.
- Are humans still evolving?
- Yes. For example, the ability to digest lactose into adulthood is studied as having spread in some populations over the past few thousand years alongside dairying.
Sources reviewed: 2026-10-26
References
- Lamarck, J.-B. (1809). Philosophie zoologique. Paris: Dentu.
- Darwin, C., & Wallace, A. R. (1858). On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection. Journal of the Proceedings of the Linnean Society of London. Zoology, 3(9), 45–62.
- Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. London: John Murray.
- Mendel, G. (1866). Versuche über Pflanzen-Hybriden. Verhandlungen des naturforschenden Vereines in Brünn, 4, 3–47.
- Dobzhansky, T. (1937). Genetics and the Origin of Species. New York: Columbia University Press.
- Kimura, M. (1968). Evolutionary rate at the molecular level. Nature, 217, 624–626.
- Eldredge, N., & Gould, S. J. (1972). Punctuated equilibria: an alternative to phyletic gradualism. In T. J. M. Schopf (Ed.), Models in Paleobiology (pp. 82–115). San Francisco: Freeman, Cooper.
- Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. The American Biology Teacher, 35(3), 125–129.
- Lenski, R. E., Rose, M. R., Simpson, S. C., & Tadler, S. C. (1991). Long-term experimental evolution in Escherichia coli. I. Adaptation and divergence during 2,000 generations. The American Naturalist, 138(6), 1315–1341.
- Grant, P. R., & Grant, B. R. (2006). Evolution of character displacement in Darwin's finches. Science, 313(5784), 224–226.