Am 30.11.2017 um 21:04 schrieb Bald Eagle:
> "omniverse" <omn### [at] charternet> wrote:
> Makes me wonder about why
>> everything that ever occurs can't somehow continue. But it's really the other
>> things like alligators and sharks that haven't changed much where it gets
>> weirder still, if evolving takes place. That's what I mean by sometimes there's
>> an end product, or so it seems, yet not the other multitude of steps along the
>> way.
> 
> Well, with things like alligators, crocodiles, coelacanths, frilled sharks,
> white sturgeon, alligator gar, paddlefish, etc. - there must not be any
> environmental pressure to induce change.  Evolution is survival of the fit -
> which means there will be variation, but if that species is already optimized
> for the environment that it inhabits, than any other mutation is a detriment - a
> "devolution" of sorts.

Also, the fact that a species hasn't changed much in appearance doesn't
mean it didn't evolve. We can't see properties like immune system or
metabolism in the fossil records.

And then there seem to be "winning body plans", which keep coming up
again and again in different species, such as the "sabre toothed cat"
pattern, which was developed by different species (including some
distinctively non-feline ones) at different times.

For some reason none of the occupants of that ecological niche managed
to get a permanent foothold there; maybe that niche has a natural
tendency to collapse from time to time. But if such recurring niches for
particular body plans exist, it is reasonable there are other niches
that remain open virtually indefinitely; and in such cases, once a
species has established itself in that niche, it is reasonable to assume
that it will be able to continue to assert that niche -- not because it
remains unchanged, but because to the very contrary it continues to
change, namely by optimizing even more for that niche (with the body
plan being pretty much finalized comparatively quickly), thus staying
ahead of any other species that might happen to enter that niche.

The crocodiles' niche appears to be just such a permanent one.

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