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WHAT IS IT?

• Natural selection is the process by which those traits of a species that give it an advantage in its environment become more common over successive generations, while those that are disadvantageous become less common. This is a major component of the theory of evolution.

• Charles Darwin used the term to describe the way nature favors certain characteristics just as humans do when we choose to breed particular plants and animals with especially desirable qualities to ensure that these qualities become typical in later generations. This breeding process is called artificial selection.

WHY IS IT IMPORTANT?

Natural selection does more than simply alter existing species; it also creates new species. The origin of life remains a mystery, but it is certain that all of the millions of species that have ever existed on Earth are descended from a single life form that came into being about 3.8 billion years ago. As this original life form became more abundant, it spread, and as it spread, different individuals encountered different environmental conditions. Over successive generations, the descendants of this original life form became differentiated to best cope with their own particular environments until, eventually, they became distinct species. Natural selection accounts for every variety of life on Earth, including our own species, Homo sapiens.

HOW DO WE KNOW ABOUT IT?

• Fossils, the buried remains of long-dead plants and animals, preserve the characteristics that defined a given species at a given point in history. By comparing fossils of the same or similar species that lived at different times, it is possible to see evolutionary change.

• Comparisons of the DNA reveal how different species are related. DNA is the genetic material that acts as a blueprint to create an organism, and the more closely two organisms are related, the more they will have identical DNA. Humans and bacteria have a very small amount of identical DNA, while the DNA sequences of humans and chimpanzees are 97 percent identical.

• Field studies reveal evolutionary change. Researchers studying finches on the Galápagos Islands, where Darwin observed different finch species with different beaks, have shown that particular beak characteristics give certain birds an advantage in their struggle to survive, these characteristics are then passed on to their offspring.