How fast does evolution happen?

When Charles Darwin developed his theory of evolution in the mid-19th century, he figured this fundamental process took place very slowly over geological timescales, taking millions of years.

But is this correct, or can evolution happen more quickly? How fast can evolution work?

First, let's define evolution, which is the process by which a species' genes or physical appearance changes gradually over time. The driving force is natural selection, in which individuals with more beneficial traits survive and reproduce, sending those traits to the next generation. Over many generations, this is known as adaptive evolution.

Combined, natural selection and adaptive evolution allow a "species to track changes in its environment," said Timothée Bonnet, an evolutionary biologist at the French National Center for Scientific Research and La Rochelle University.

In the famous example of Darwin's finches on the Galápagos Islands, different species evolved different beak shapes and sizes within a few decades to specialize in feeding on different types of nuts and insects. This finding made waves following the publication of the Pulitzer Prize-winning book, "The Beak of the Finch: A Story of Evolution in Our Time" (Knopf, 1994).

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Then, there's a third component: speciation. This is when one species branches off into two distinct species over time. Bonnet said this happens much more slowly than adaptive evolution.