Nature appears to be able to evolve the same sets of complex traits over and over again. The process by which strikingly similar traits which have the same functions evolve independently is called convergent evolution. For example, echidnas in Australia look incredibly similar to South American anteaters when in fact they are more closely related to the platypus. Even entirely different genes can be used to perform the same function; fish in the Arctic and the Antarctic produce the exact same antifreeze proteins using different genes. Convergent evolution has been used both to support the intelligent design argument (these complex traits could not have evolved several times by mere accident) and the argument that there cannot be a conscious designer as such a designer would not start from scratch to create a solution to a problem which they had already solved!
Convergent evolution could be telling us that evolution is not an accident but rather a manifestation of deep laws of nature. In the popular perception of Darwinian evolution an organism is thought of as a collection of parts, each part having come into existence via an accidental mutation. Charles Darwin actually believed that this interpretation caricatured and trivialized his theory. Darwin devoted large sections of his book Origin of Species to describing the underlying unities in nature. He believed that natural selection was just one of several means by which evolution occurs, although natural selection is perhaps the most important. Rather than an accident, Darwin also saw natural selection as a law of nature much like gravity. This common misinterpretation I believe is at the root of a lot of arguments about evolution today. Examples of convergent evolution include:
Poison Dart Frogs: These frogs have evolved identical poison skins in both South America and Africa. Their dazzling patterns are also amazingly similar on both continents.
Camelids: (a group of animals that includes camels and llamas) have independently evolved an identical antibody protein also found in nurse sharks. This is an example of convergent evolution in very distantly related animals.
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