Our Human Story: An Introduction to Biological Anthropology · LibreTexts
0%
Contents
Text
Size
From LibreTexts, under CC BY-NC 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.
3.4: Evidence
Opening the book…
Darwin didn’t ask anyone to take natural selection on faith. He built his case on multiple independent lines of evidence, and each one still holds up under modern scrutiny.
Evidence from Geography
The Galapagos tortoises gave Darwin a clean natural experiment. Tortoises on larger islands with abundant, low-growing vegetation had shorter necks and dome-shaped shells, since their food was close to the ground. Tortoises on smaller, drier islands, where food was mainly tall cactus, had longer necks, longer front legs, and saddle-shaped shells that let them stretch upward to reach it. Different islands produced different selective pressures and different outcomes, all in populations that had descended from a shared ancestor. Darwin observed a similar pattern among the islands’ finches, whose beak shapes varied with the food available on each island.
Figure \(\PageIndex{1}\): Galápagos finches differ in beak size and shape, depending on the type of food they eat. Image by: Bioanthropologist1, CC BY 4.0 via Wikimedia Commons.
Evidence from Fossils
The armadillo fossils Darwin found in Argentina, extinct forms buried in the same region where living armadillos still roamed, undercut the idea that living and extinct forms must always be unrelated, separately created species. Darwin acknowledged that the fossil record of his day was full of gaps, missing many of the transitional forms that would bridge ancient and modern species. Since then, advances in paleontology and geochronology (methods for dating rock and fossils) have filled in a great many of those gaps, and it is now well established that life is far older, and far more continuously connected across time, than Darwin himself was able to prove (Kutschera and Niklas 2004).
Evidence from Selective Breeding
Perhaps the most immediately visible evidence for the power of selection is one anyone can observe today: dog breeds. Every domestic dog, from a Chihuahua to a Great Dane, belongs to the same species, Canis lupus familiaris. They are all descended from wolves, reshaped almost entirely by human-directed selective breeding over the span of a few thousand years, which is a blink of an eye in evolutionary terms. If artificial selection can produce that much change on that short a timescale, it becomes far easier to imagine what natural selection can do over millions of years.
Figure \(\PageIndex{2a-d}\): A variety of domestic dog breeds that are all the same species, Canis lupus familiaris. From left: a) a Chihuahua, Image by Manuela Federspiel from Pixabay; b) a French Bulldog, Image by Fabian Köhler from Pixabay; c) a Welsh Corgi Image by Andrey Muzychuk from Pixabay; d) a Great Dane Image by Martin Tajmr from Pixabay.
Evidence Darwin Never Saw
Darwin had no idea what a gene was. DNA wouldn’t even be identified as the molecule of heredity for nearly a century after his death. Yet everything discovered since — genetics, molecular biology, the mapping of the human genome — has consistently supported and refined his framework rather than overturning it. We’ll explore exactly how heredity works at the molecular level in the next chapter. For now, the important point is that an idea proposed with 19th century tools has held up remarkably well under 21st century scientific scrutiny.
This page titled 3.4: Evidence was last modified on Thu, 20 Aug 2026 00:23:13 GMT and is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Rachel Mitchell.
