From: Tony Williams 

Tim Boyer wrote:
> On Mon, 22 Aug 2005 18:31:41 -0400, "Geo"
 wrote:

>>This is where i have a problem with the "evolution tries all
possibilities"
>>in that it never seems to try backtracking. I mean somewhere sometime there
>>had to be something that was previous to what exists today that is now
>>viable again.
>>
>>Ok, perfect example, why haven't dinosaurs reappeared? I mean if a meteor
>>knocked them out, now that the air is clear and things are returning to the
>>same temperature ranges and such, why haven't they reappeared?
>
> Because something else evolved to take up their niche.
>
> Pesky mammals...
>

Exactly. It's a race between species to control a niche; the winner
continues to develop whatever traits work in than niche while the loser
either becomes extinct or loses the specialisation by evolving back to
where they started.

Flightless birds started out being unable to fly, tried it for a while and
then lost the ability. You could say that they evolved past flying, but
it's undeniable that they gained an ability and later lost it.

--
Tony

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