Explainer: 7 signs of evolution in action

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    Spencer Arnold  /  Getty Images file

    British naturalist Charles Darwin's groundbreaking 1859 book, "The Origin of Species," proposed the theory that species evolve over time through the process of natural selection. Organisms most suited to their environment survive and reproduce, passing on their advantageous traits to offspring. Organisms that cannot compete go extinct. Though this theory remains a hot potato in the culture wars, it forms the foundation of modern biology. Click the "Next" arrow above to see seven signs of evolution in action.

    — By John Roach, msnbc.com contributor

  • Darwin's finches evolve

    Image: Elah Fortress ruins
    B. Rosemary Grant  /  Science via AP file

    The seed-crushing bills of little songbirds called finches, which were adapted to various niches throughout the Galapagos Islands, proved integral to the formulation of Darwin's theory of evolution by natural selection. And the birds haven't stopped evolving. For example, the medium ground finch (Geospiza fortis), shown here, recently downsized its beak to exploit small seeds more efficiently after a larger finch arrived on its island and began competing for food. The smaller beaks on the smaller birds allowed them to thrive, while the big birds ate all the big seeds and nearly went extinct, scientists say.

  • Humans influence natural selection

    Image: pottery shards
    CNBC TV

    Is human activity "natural"? Scientists say human activity is indeed affecting the evolution of other species. In one example, the human preference for large snow lotus plants, which are used in traditional Tibetan and Chinese medicine, has meant that only the smaller plants go to seed. Hence, the snow lotus is getting smaller. In another example, scientists have found that human preference for trophy game such as big fish and caribou is driving these species to become smaller and reproduce at younger ages.

  • Human evolution speeding up?

    Image: water flows through remains of Siloam Pool site
    Hulton Archive  /  Getty Images file

    With more people crowding into ever more ecological niches over the past 10,000 years, humans appear to be evolving more rapidly than in the distant past, according to scientists. What's more, as people adapt to different regions, cultures and diets, they are becoming increasingly different from people elsewhere. For example, Europeans have evolved a tolerance for dairy products into adulthood, whereas people in China and most of Africa have not.

  • Butterflies evolve resistance to killer bacteria

    Image: Dead Sea scrolls
    Sylvain Charlat / Science

    A population of tropical butterflies on a South Pacific island evolved resistance to a killer bacteria in the span of a single year — a blink of the eye in evolutionary time. The bacteria infects females and selectively kills males before they hatch. The strategy reduced male Blue Moon butterflies to just 1 percent of the population. But just 10 generations later — a year's time — males made up nearly 40 percent of the population. Scientists said the rebound is due to the evolution of a so-called suppressor gene that keeps the killer bacteria in check.

  • Toxic toad evolves longer legs

    Image: sarcophagus
    Ben Phillips

    A toxic toad, introduced in 1936 to wipe out a beetle species wreaking havoc on Australia's sugar cane crop, has become an uncontrollable pest itself, evolving longer legs to help it hop across the country at an ever-increasing clip. For their first 20 years or so in the country, they spread at a pace of 6 miles per year. They now cruise at about 30 miles per year. Why? Researchers found that the toads leading the cross-country march had legs that were 6 percent longer than those of the stragglers. The added length gives more speed, which permits the long-legged toads to secure the best habitat at the newly conquered terrain.

  • Intermediate form supports flatfish evolution

    Image: drainage channel

    Flounder, sole, halibut and other flatfish have long struck biologists as evolutionary oddities: Both their eyes are on one side of the head, an adaptation that allows them to lie flat on the ocean bottom while keeping their eyes on the lookout for passing prey. The transition happens in the youth of flatfish, one eye migrating up and over the top of the head. Opponents of evolution argued that this curious anatomy could not have evolved gradually, as suggested by the theory of natural selection. That's because there would be no advantage for an intermediate form — a fish with an only partially migrated eye. But now scientists have found those intermediate forms in museum collections. The 50 million-year-old fossils, including Heteronectes chantei shown here, have a partially displaced eye.

  • Lizards lose limbs

    Image: archaeological site in Masada
    Mark Hutchinson

    Australian lizards called skinks are dropping their limbs to become more like snakes. And, according to a genetic family tree, some skinks have gone snaky in just 3.6 million years, relatively fast in evolutionary time. Scientists said the skinks' lifestyle appears to be driving the change: They spend most of their time swimming through sand or soil. Limbs are not only unnecessary for this, they may be a hindrance. Once a skink goes snaky, they never go back, the researchers add. One of the snakelike skinks is shown here.

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