It is very difficult to evolve by altering the deep fabric of life; any change there is likely to be lethal. But fundamental change can be accomplished by the addition of new systems on top of old onesThus evolution by addition and the functional preservation of the preexisting structure must occur for one of two reasons-either the old function is required as well as the new one, or there is no way of bypassing the old system that is consistent with survival.

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About Carl Sagan

Carl Sagan was a 20th-century American scientist and science communicator. Carl Edward Sagan was an American astronomer, planetary scientist and science communicator. Initially an assistant professor at Harvard, Sagan later moved to Cornell, where he was the David Duncan Professor of Astronomy and Space Sciences and directed the Laboratory for Planetary Studies. Read more on Wikipedia →

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