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Re: Back-evolution of limbs.

At 08:43 PM 6/27/98 -0400, John Bois wrote:
>I don't know whether the following has been discussed before, but:
>Why is it that birds--and only flying birds at that--are the only
>creatures to return to their former mode of locomotion, i.e., they may
>become secondarily flightless.
>I haven't heard of a bat or flying squirrel doing such a thing.
>And I don't know of any swimming mammal or bird which has returned to a
>terrestrial existence.  Why, for example, has no seal colonized some
>competition and predator-free island and redeveloped structures for
>Perhaps there is a unidirectionality to limb evolution.

Whales were land animals, their legs evolved back into flippers.