Evolution Timeline

Where do we see evidence of evolution?
Answered by Discovery Channel
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    Discovery Channel

  1. As organisms evolved, they usually adapted to function better in their environments. It's all part of natural selection. Vestigial or rudimentary organs and structures are examples of adaptations in organisms' ancestors that eventually evolved to be nonfunctional [source: Berkeley]. Sometimes, a species' ancestors had a particular organ or structure but its modern counterparts no longer needed the organ or structure for survival. For example, many species, such as tetra fish, live in dark caves have vestigial eyes. In other words, they evolved from a species with eyes but no longer need them in their dark environment and the eyes don't function. That's probably because the dark environment caused the fish to develop -- out of necessity -- such outstanding senses of taste and smell that their sense of sight simply deteriorated. Sometimes, vestigial organs are detected in embryos but are no longer detected at birth. An example is teeth in whale embryos' upper jaws [source: New York University].

    Another good example of evolution in vestigial structures is something you may not see often, unless you're inclined to picking up pythons and boa constrictors and turning them over to observe them "up close and personal." If you do, you'll find tiny hind leg bones tucked into the muscles behind the ends of the snakes' tails. These powerful crawlers don't need legs, so they're considered useless. So what do they have to do with evolution? Snakes come from lizards. More than 100 million years ago, some lizards developed smaller legs that actually helped them maneuver over certain geography. The legs kept getting smaller through successive generations as they weren't used, until the new form of lizard developed with only vestigial legs remaining [source: American Museum of Natural History].  We even can see indirect evidence of evolution in our own species. All animals with a backbone, including humans, encounter a developmental stage where they have gill clefts, suggesting they evolved from creatures that lived in the water.

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