Re: Of whales, gills, and the nested hierarchy

On Sep 1, 6:15 pm, morgoth...@xxxxxxxx wrote:
Hi, question about evolution. Animals can be categorized into an
objective nested hierarchy, which is the pattern produced by descent
with modification from common ancestors. We wouldn't expect complex
traits to arise twice independently, so finding an insect with
vertebrate eyes, a mammal with bird feathers, or a kangaroo with a
placenta would be a shock and would, afaik, basically call into
question much of what we think we know about evolution. Does this
principle also work for traits that did exist in a lineage, then were
lost? Whales are descended from terrestrial artiodactyls and
therefore have lungs, but (much) further back are descended from flesh-
finned fish, which had gills. Would it be possible for gills to
reappear again? Would finding a gilled whale violate the nested
hierarchy? Or is the gill-making machinery still in the genome and
latent?

Your example isn't very good because gills do not provide nearly
as much oxygen to the user as air lungs do.

Basically however the answer is yes and no depending on the
details:

1) If lungs that were functionally, morphologically and genetically
identical (or nearly identical) to fish lungs re-evolved it would be
a violation. The pre-existing code to make lungs has long since
been lost, or been co-opted to make other structures. (Note that
we are looking here at a gap of about 300 million years since whale
ancestors last had lungs - for a shorter period of maybe 500,000 years
or [probably a lot] less, re-emergence of a characteristic might
be possible.)

2) If lungs that were substantially different from fish lungs (say as
different as mammal eyes compared with anthropoid/insect eyes ) re-
evolved in
whales it would not be a violation of the nested hierarchy, provided
of course that those new lungs evolved from structures that now
exist in whales.

.

Relevant Pages

  • Re: Of whales, gills, and the nested hierarchy
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