DNA Question

Guy Hoelzer hoelzer at med.unr.edu
Fri Dec 11 15:09:09 EST 1998


In article <74muup$f7k at net.bio.net>, Mary K. Kuhner
<mkkuhner at kingman.genetics.washington.edu> wrote:

>In article <74mr7j$58h at net.bio.net>, Guy Hoelzer  <hoelzer at med.unr.edu> wrote:
>
>>However,
>>environmentally induced phenotypic changes are generally not considered
>>evolutionary, in part because they are easily reversed.  For example, body
>>size can often be influenced by temperature (or feeding rate) during
>>development.
>
>There are at least a few examples of more strictly heritable changes,
>however.  If you peel a strip of cell surface off a ciliated paramecium
>and put it on backwards, so that the cilia are pointing the other way,
>they will stay backwards, and the offspring of the cell will have
>strips which are backwards--indefinately, at least until you go at them
>with another razor blade.  The basal bodies of the existing cilia are
>apparently used as templates for constructing the new ones.  Thus,
>cilium direction is heritable without reference to the DNA.

You provided an excellent example of environmentally induced evolution
without genetic change.  I am convinced by your example that it is
possible.
>
>We don't really know how common this kind of non-DNA inheritance is.  

I agree, but I feel pretty confident in predicting that it is very rare
compared with genetically induced evolution.

>It's conceivable that you could have some trait maintained by mother/
>child interaction in a very strict, fixed fashion, but with no DNA
>involvement, so that it could be drastically changed without DNA
>changes.

You make another good point here.  I agree that non-genetically based
mechanisms of inheritance exist and explain much of cultural evolution. 
However, if I am correct, the original question was aimed specifically at
morphological evolution.  While it is certainly true that cultural
practices can influence morphology, and therefore morphological evolution
could hitchike along with cultural evolution, I suspect that such
influence rarely changes morphology much.  That is, the influence of
cultural practices on morphology is minor compared with genetic influence
on morphology.  In addition, the pace of cultural evolution probably makes
such an influence look like noise on the long-term effects of genetic
change on morphological evolution.  Nevertheless, your points are well
taken.

-- 
Guy A. Hoelzer                 phone:  702-784-4860
Department of Biology          fax:  702-784-1302
University of Nevada Reno      email:  hoelzer at med.unr.edu
Reno, NV  89557




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