chimp speciation

Alex Duncan (
25 Oct 1995 03:46:56 GMT

In article <> Paul Crowley, writes:

>So surely the assumption that a species has not changed substantially
>since its initial speciation is much more than a null-hypothesis?
>If we know that blue tits, or blue whales, or species X existed
>five million years ago then, in the absence of evidence to the
>contrary, surely it is safe to assume that their behaviour and
>morphology has not changed in that time?

We may not have evidence from the fossil record that speaks to this
issue, but we do have molecular data, which tells us that the genus Pan
(P. troglodytes, P. verus & P. paniscus) probably originated about 2.2
Myr ago. (This number is little old, and may have been updated. I'll
check.) There is a fair amount of variability within this group, so
assuming that "chimps" haven't changed for 5 Myr begs the question "which
chimp?" But also, and obviously, the data indicates recent (last 2.5
Myr) speciation events within the chimp lineage.

In general, large bodied mammalian species are thought to have a
longevity of about 1 Myr (any updates or comments on this number?). I
think this qualifies as evidence to the contrary. In the absence of any
other data, we should expect that there have been at least 5 speciation
events in the chimp lineage since 5 Myr ago. In other words, it is not
parsimonious to assume that "chimps" of 5 Myr ago were like chimps today.
Because we don't have a fossil record for chimps we are limited in our
speculation, and from a cladistic perspective, it is somewhat
unparsimonoius to assume any changes between the chimps of today and the
"chimps" of 5 Myr ago, simply because we don't have any good ideas about
the nature of the changes that might have occurred.

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086