[Taxacom] DNA homologies

[John Grehan]

> From: Steve Manning [mailto:sdmanning at asub.edu]
> Sent: Tuesday, September 26, 2006 6:19 PM
> For what it is worth, I suggest you make clear what you mean by
> "theoretical" throughout the previous paragraph.  

I'll see what I can do. Thanks. By theory I probably mean to emphasize
assumptions made in the process. Of course molecular and
macro-biological studies both have assumptions built into their
methodologies, but it seemed to me that there were more layers of
assumption (i.e. assumptions are built up on preceding assumptions)
involved in the molecular approach. Then again it all depends on what
labels as an assumption and whether the numerical result is can be
objectively agreed upon. Perhaps one persons assumptions represents to
another person two or more assumptions. It may be that I a wrong to view
molecular systematics having more layers of assumption. That will be for
future debate. 

> I think it would be interesting to attempt to learn of paleoclimates
in
> which chimpanzees, humans, and orangutans evolved, based on
> paleobiogeography; note differences, and see if any of them correlate
with
> morphological or molecular differences, possibly resulting in stronger
> selection for some of those features in one group than another.  

These things might be interesting, but already there is an assumption
built in, that correlations between environment and differences in
molecular or morphological differences are involved with selection.

For
> example, did the probable available diet of chimps or orangutans
differ
> enough that certain oral features became more important for survival
in
> one
> than the other?  

Or did either already have features that 'pre-adapted' them to such
changes. But either way, it may not matter since what is at stake is
what the common ancestor had. The orangutan is not the common ancestor
of humans, so any evolution within that lineage does not involve the
human lineage. And if the common ancestor of humans and orangutans was
already in Africa, then it may have been exposed to the same ecological
and environmental conditions as the modern African apes, or it may not -
depending on whether they existed in the saem ecologies or even same
region (it is possible that the modern African apes never ranged over
East Africa for example).


I think the unspoken
> assumption, justified or not, usually is that macromorphological
features
> are more strongly selected than molecular features -  tending to lower
the
> probative value of morphological features compared to DNA evidence
when
> they conflict. I think until proteomics is further developed that
> assumption is hard to test. (?)

I would agree, although I don't know whether it is a testable
proposition at all since it involves making a determination of how
particular mutations spread through a historical population 
> 
> Basically true - I think attempting to quantify the probabilities of
> certain events
> could help, even if only to force people to examine their assumptions.

For that end I would certainly agree. Thanks for the feedback. Now if
only I can get past the censors and get the article published in a
widely read journal!

John Grehan