Re: Brain development.

Thu, 2 Feb 1995 21:52:00 PST

Nicholas writes in response to earlier posts on hominids having a unique
adaptation based on intelligence:

"If more than one species developed an advantageous asset ['intelligence']
that would enable them to occupy the *same* niche then they could fill the
niche until the system could no longer support their similar activity. It
would be then that subtle advantages would enable one species to survive and
the other to become extinct.

Is this not the case for early hominids with Modern Man as the result?"

First of all, to say that hominids have an adaptation based on "intelligence"
in contrast to other species is not very helpful. Intelligence is a vagues
term that refers to what it is the brain can do, and all species with a
brain have an adaptation based on 'intelligence.' What seems to distinguish
us is our capacity to utilized an extraorinarily wide range of resources;
as out "niche width" expanded through time, the potential for speciation may
have equally diminished since an adaptation based on a wide "niche width" in
effect precludes another species also based on "niche width" and using a
resource base not yet utilized by the first species.

In terms of hominid evolution, we need to distinguish between allopatric
"species" which are largely a creation of taxonomic labeling and irrelevant
to arguments about species comptetition and sympatric species where
competition for resources can develop. As we track hominid evolution through
time, the number of sympatic species is still in dispute. For the time
period 4 mya to about 1.5 mya, we know that we at least had two symptric
species (the lineage eventually leading to ourselves, a lineage charaterized
by, e.g. A. boisei, at a minimum). One scenario is that the "A. boisei"
lineage died out by virtue of its resource base disappearing--its trajectory
suggests that it was specialilzing on a diminishing resource base (the very
large teeth that developed over a very short period of time) and may have
gone extinct simply by its resource base diminishing (hence the reason for
the specialilzation). To what extent there was species competition is
debatable, hence the extent to which species competition was a driving force
for evolution in the lineage leading to us for this time period is unclear.
If we jump ahead in time to around 500,000 years ago we may have had a single
hominid lineage; if so, further evolutionary development was not driven by
sympatric hominid species competition.

D. Read