>3. Because the rate of mutation is constant in time (vs. number of
>generations), mutations must be caused primarily by random chemical changes
>or radiation damage than be replication error. If replication error were
>the chief source of mutation then organisms with short generation times
>(insects, bacteria, yeast, etc) would show faster change and this would
>disrupt the linearity of the molecular clock.
I'm not sure what you mean here, Terry. I presume that by 'chemical
changes' you mean mutagens? If so, both mutagens and radiation promote
replication error and are quantitated as a function of generation time (at
least in cell cultures). For a hypothetical unicellular organism growing in
some primordial soup (or slime according to Augustine), replication error
would, therefore, be a function of its environment.
>
>4. Both branches of a lineage following a divergence event continue to
>accumulate mutations at the same rate. Thus fish continue to accumulate
>amino acid substitutions along with new groups (mammals, reptiles) that
>descended from ancestral fish. Consequently, the present day members of
>more primitive groups are equidistant from another organism on an outlying
>branch. Some people find this surprising and claim that because it is so
>that the sequence data do not support evolutionary theory (see Michael
>Denton, _Evolution: A Theory in Crisis_ and _Pandas and People_, a high
>school biology textbook supplement that criticizes evolutionary theory and
>argues that the failure of evolutionary theory points to a Creator God).
>This view commits the error that ancestral groups stopped evolving (at the
>molecular level) following a divergence event.
This is an important point. I continually encounter people who think that
evolutionary theory implies that humans evolved from apes. The correct
scenario from evolution would be that humans and apes evolved from an
earlier ancestor and are equidistant in the evolution continuum.
Cheers,
Steve
__________________________________________________________________________
Steven S. Clark, Ph.D. Phone: (608) 263-9137
Associate Professor FAX: (608) 263-4226
Dept. of Human Oncology and email: ssclark@facstaff.wisc.edu
UW Comprehensive Cancer Ctr
University of Wisconsin
Madison, WI 53792
"Universities are full of knowledge; the freshmen bring a little in, the
seniors take none away...the knowledge accumulates." Mark Twain
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