Re: CB928.2: Humans evolving
- From: "A.Carlson" <amcarls@xxxxxxxxxxx>
- Date: Mon, 03 Oct 2005 20:28:58 -0700
On Tue, 04 Oct 2005 02:03:00 GMT, Harlequin <usenet@xxxxxxx> wrote:
>"VBM" <v.mcalister@xxxxxxxxxxxxxxx> wrote in
>news:Aqj0f.6083$zQ3.3906@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx:
>
>[snip]
>> In clinical practice, dentists often assume that teeth which are
>> frequently missing or variable in form are 'on the way out' in
>> evolution. Is this a valid statement? If we set it up as a testable
>> hypothesis, it might be stated as follows: teeth destined for
>> evolutionary loss anticipate that condition by increased variability
>> in size, shape, and/or agenesis. Supporting evidence would be strong
>> selective pressure toward loss of a tooth in evolution. Another
>> evidence might be a series of consecutive fossil specimens as evidence
>> of progressive tooth loss. I am not aware of such studies.
>[snip]
>
>
>I would say it is massively invalid. It assumes past evolutionary
>trends must continue.
>
>What this sounds like to me is very old discredited concept:
>orthogenesis. That one died with the development of the
>Modern Synthesis. I will let you google the terms.
For natural selection to work, one needs variety to begin with. If
there is variety across the board it stands to reason that certain
environmental pressures may have an effect across a population as a
whole under the right condition.
The peppered moth comes to mind here. If the peppered moths were
still subject to heavily sooted trees, wouldn't some 'past
evolutionary trend' be expected to continue to select for the darker
variety of moths from throughout the population?
The fact that there is variety in the number of molars among the
population certainly makes this seem at least like a possible feature
that can be simultaneously selected for.
I would think that those with missing molars would be far less likely
to suffer problems related to incoming wisdom teeth with little
negative aspects due to both better oral hygiene (I suppose if we
ignore the British and the Japanese ;) and the fact that our diet for
a long long time (eating utensils included) has consisted of highly
processed and cooked foods which would tend to lessen the significance
of lost molars.
Perhaps the variation in the number of molars that exists now to some
degree may be an indication of forces that have been at work perhaps
for centuries. (Just an unsubstantiated hypothesis)
.
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