> I agree. Recombination of genetic traits at reproduction has been
>the only usefull avenue. My son looks more handsome than I, but he doesn't
>have a third arm or nostril or a third lung or anything new except for
>traits that have been in my family and my wifes for years that have
>nothing to do with mutations but everything to do with reproduction.
> Is there an example of otherwise?
> john w queen ii
Yes there are examples of otherwise. Some of the most dramatic examples of
how minor genetic changes can cause major phenotypic alterations are found
in developmental biology labs. Minor genetic alterations have totally
rearranged the organization of body plans and wing formation in insects.
Eyes have grown inside a frog's mouth, other body parts have been placed in
unusual locations. The relevance that all this has to evolution is to
demonstrate that small genetic changes can result in major alterations.
When this happens inside the lab, the unusual phenotypes are generally
advantageous for the simple reason that the researcher selects the mutants
and discards the less interesting variants or normal animals. This is an
example of how mutation can affect a phenotypic change that provides the
organism with a selective advantage (albeit the selection is "artificial").
Now the question becomes, can similar processes result in selection of very
distinct morphotypes under "natural" selection. Well, the answer is that it
depends upon whether or not the mutation produces an adaptive phenotype.
Population ecologists would argue that most species which exist at a given
time, represent those best suited for the environmental niches that are
available. It is further argued that when the environmental niches become
drastically altered, then the selection pressure increases, and at that time
one would find evidence for rapid speciation. Some say that the evidence
from the fossil record supports this contention that tremendous speciation
followed large environmental events.
Under this explanation, in the absence of large changes in environmental
niches, one would not expect to often find examples of evolutionary change.
The fact that "naturally" ocurring mutations that we observe to result in
significant changes in phenotype are usually deleterious, is also consistent
with the notion that in a relatively constant environment, selection
pressure is not sufficient to drive major morphological changes.
It is important to keep in mind that this is a model that is supported by
some data, but that also suffers from the absence of other supporting
data--such as direct observation of evoloution of lungs in fish, for
example. It is also important to keep in mind that the absence of such
observational data is not inconsistent with the model, and to cite such
holes in the record as convincing evidence against the model is not a very
compelling argument.
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 Center
CSC K4-432
600 Highland Ave.
Madison, WI 53792
"It is the glory of God to conceal a matter, but the glory of kings to
search out a matter." Proverbs
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