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One reason Darwin's theory of evolution by natural selection is widely accepted today is that there's a large amount of evidence to support it. Evolution leaves observable signs as clues to the past.

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Since Darwin's time, fossils have been used to support the Darwinian theory of evolution. Fossils help scientists establish the order in which other organisms appeared, even if an organism is now extinct. Scientists can also see how similar organisms have changed over time.

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One of Darwin's many important observations was that species of one area are closely related to the species in the neighboring areas. Darwin believed the Galapagos finches were species that had evolved from South American finches that had colonized the islands. Over time, the finches adapted to their new environments and became unique species.

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A strong piece of physical evidence supporting Darwinian evolution is the anatomical similarities among different species. Humans, whales, bats, and all other mammals have similar forelimbs. The structures of the forelimbs are similar, even though they perform very different functions. Some organisms possess vestigial structures, ancestral structures that have lost their use. For example, some snakes have remnants of a pelvis and legs, leading scientists to hypothesize that they evolved from lizards.

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One type of information scientists in Darwin's time didn't have at their disposal was molecular evidence. Today's scientists are able to compare the DNA or protein sequences of organisms. Organisms that are closely related through evolution have similar sequences in certain proteins. In addition, certain fundamental processes, like cell division, have been conserved throughout evolution: from yeasts, to plants, to mammals— including humans.

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Because evolution occurs over millions of years, the process can't be reproduced in a lab. However, there are many examples of natural selection at work. A good example is the change in the English peppered moth population after the Industrial Revolution. Peppered moths spend much of their time on birch trees.

Before the Industrial Revolution, 99% of the moths were light colored, so they blended in with the light-colored trees. Dark moths stood out and were much easier for birds to catch. The dark moths didn't survive to have many offspring. The Industrial Revolution introduced many soot-producing factories. The soot coated the birch trees, making them black. Now the light-colored moths stood out, and were less likely to survive. After the Industrial Revolution, 99% of the moths were dark.

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Artificial selection is another example of selection at work. Artificial selection is used in the selective breeding of domesticated plants and animals. Farmers selectively breed cows to increase milk production and to generate leaner beef. Crops are artificially selected for higher yields and for taste. Flowering plants are selected for their large, showy flowers. With artificial selection, animal and plant characteristics can be changed in just a few generations. This suggests that the same phenomenon could occur over thousands of generations through natural selection.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education