> Finally, even if black-backed jackals have unusual rates of
>mutation in mtDNA, it still may be relatively constant in other lineages.
>There's no a priori reason why mutations should occur at a constant rate;
>each case needs checked against the fossil record.
But that at least introduces an uncomfortable circularity. In this case
the fossil record of jackals is pretty well known, but it probably is
difficult to tell when the fossil is a "black backed" jackal. The authors
have asserted as you do that there are too many variables and unknowns to
be able to use mtDNA as a chronometer.
> Any "molecular clock" needs tested within the taxonomic group under
>consideration before any credibility should be given to it. I don't know
>if it's the high ratio of molecular biologists to paleontologists, but
>molecular-clock based dates get far too much credibility relative to the
>fossil record. Inclusion of error bars for the dates would help.
Exactly. And it probably is the ratio that is part of the problem. Try to
make a living as a paleontologist, and you will discover it rates right
alongside marine biology.
Art
http://chadwicka.swau.edu