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ProfessorPlum Donating Member (1000+ posts) Send PM | Profile | Ignore Tue Nov-30-04 04:11 PM
Response to Reply #297
301. Thanks
It's OK that most mutations are negative, though, and to be expected. You only need a positive one once in a while. Even a negative mutation can become a positive one as conditions change, eg sickle cell anemia and malaria.

The half a billion year time period is only the time it takes to get life going. If I remember correctly, the earth is about 4.5 billion years old, and we keep finding older and older fossils of single celled organisms, going back almost 4 billion years. So the half a billion years is all pre-evolutionary time. The 4 billion years since the evolutionary clock started ticking was mostly filled with single-celled organisms, followed by the Cambrian explosion when all known modern phyla appeared in the fossil record. Most of evolution after that has been extinction of some branches and brachiation of others. But it's a hell of a long time, certainly long enough to account for current complexity.
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