In article <1le4gp$bav at gazette.bcm.tmc.edu>, steffen at mbcr.bcm.tmc.edu (David Steffen) writes:
>(deleted intro)
> In-Reply-To: Message of Tue, 9 Feb 93 19:08:20 UT from
> <server-daemon at daresbury.ac.uk>
> Status: ORr
>> I see that there is an ever going controversy about the mouse-rat divergence ti
> me. the controversy is solely due to the fact that up to now there were very mi
> mited paleontological evidences to calibrate the clock in rodents, and that mos
> t of the people are using circular arguments and citations holding all the time
> on erroneous data. The good calibration CANNOT come from molecular data since
> we have no independent estimate of the speed of the molecular clock in murids.
> it has to come from the paleontology. there are some convincing evidence that r
> at and mouse diverged between 9 an 12 MY BP:
> Jaeger,JJ, Tong, H & Denys C. 1986. C.R.Acad. Sci. Paris 302 (ser.2) 917-922.
>> F. Bonhomme
> Univ. Montpellier
>Two questions: (Old ones I know but it is good to see this newsgroup
talking again)
1. My basic understanding of morphological traits (the source of your
paleontological data) is that their phenotypic expression is the
result of the interactions of genotype and environment. How could
one ever propose to accurately calibrate a molecular clock (if such
a thing exists) if you know nothing of the GXE interaction? Plus it
looks like you would need some basic information on heritability etc.
I would question the ability to extrapolate these types of values from
extant species.
2. Due to the lack of a contiguous fossil record for most modern species, it
appears to me that the paleontological-based evolutionary hypotheses that
exist for rodents are very weak and inherently unstable topologies. From
my readings it seems that paleontological arguements are no less circular
than molecular. Do you expect the fossil data to be greatly improved in
the near future? If not then it appears to me that we are currently on
a reasonable course relative to testing hypotheses regarding the molecular
clock. Namely, rejecting various hypotheses given the data at hand, as
circular as it may be.
My $0.02
Mike
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| Michael C. Wooten
| Dept. of Zoology
| Auburn University
| Auburn, AL 36849-5414
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