Re: A Question About Insects and Vertebrates

From: Malcolm (malcolm_at_55bank.freeserve.co.uk)
Date: 09/18/04 

Date: Sat, 18 Sep 2004 17:22:41 +0000 (UTC)

"Ambient Mind" <ambient_mind@yahoo.com> wrote
>
> The human body has three central weights: the head, the torso or rib-cage,
> and the pelvis. This is like the structure of an insect with its head,
> thorax, and abdomin. But what I recall of university biology was that
> vertebrate evolution diverged from that of insects long before the
> development of this type of body structure in either group. So is this an
> example of convergent evolution? If so, in response to what forces?
>
The university biology is out of date. It is now known that there are
homeobox genes, or "hox" genes, which are very highly conserved across
animals and which seem to be involved in regulating the gross body plan.
Both insects and vertebrates have a fundamental segmented structure (you can
see this if you look at fish muscle, or the pattern of nerves on a human
torso, or even more obviously in insect larvae).
The explanation cannot be convergent evolution, but that both phyla evolved
from a segmented ancestor.