----- genetic adaptation to vertebrate meat in humans is not extremely
likely (a quick search on the internet reveals that even the heme iron issue
is irrelevant, since for example clams and oysters contain heme iron).

i  might agree with you that we can be well eating non vertebrate only as
animal source of food   but there is i think enough demonstration that
vertebrate eating have been in our diet for a very long time  to be sure of
an adaptation  ( 2 and half milion years ago we had tools already for that )
and as Francois said you don't even need tools to have access to meats left
by  or stolen from carnivorous animals .( i for ex without effort stole a
pigeon killed by a crow , or a  crab or dead deer from eagles , easy without
no more than my presence ).
are  eggs  vertebrate or not .Easy to get .
so most likelly the habit  developped by our ancestors is older than our
species itself .
i eat lot of invertebrate myself but am still very attracted by red meats
also . and i love shrimps  crabs and clams
jean-claude