Erik Hill wrote:
>Amadeus --
>My understanding of how evolution works, is that bottlenecks,
>coupled with an extreme environment (an environment very
>different than the environment that was before), can bring about
>very, very rapid changes in the gene pool of an organism.
I understand that such a evolutionary bottleneck works by
selecting out such individuals of a species, which can't
stand a certain stress. It works by "deleting" or killing
such individuals in which a certain survival property
(genetic or behaviour) is not available.
The genetic variation becomes smaller, but bearers of a special
"fitness" gene get increased changes, improving the proportion
of such gene bearers in a species.
>...then the new gene pool is determined only by those
>who survived (of course) no matter how different they were than
>the previous population.
Or they die off, then the bottle is closed.
Like for neanderthals or homo erectus branches.
If a trait (the surviving people) lack the ability to stand
other (previous) situations.
But i think it (the genetic ability to cope the stress)
must be present from before, because the chances
that there's a spontaneous mutation enabling to cope with a
stress are very low. Most mutations tend to kill or decrease fitness.
>If the ice age were such a pressure,
>then the changes could have been profound, and rapid.
I agree and can see that the ice age in northern areas (europe)
presented such a bottleneck for the humans in this areas.
In ice age winters, the humans living there must have had the
ability to rely on "thinuit" (inuit like) nutrition of meat and fat.
Even if it was only for 800 generations (2 generations selecting out
will be enough).
This is not unprobable for primates, because there
was the ability to digest insectes, convert protein to the necessary
glucose (for the brain to work) and other tissues can use fat
for fuel. Human traits unable to do this (beyond a
successful reproduction) surely died off in northern areas.
However, that only means that all (northern stemming) humans
can *stand* such a nutrition.
It doesn't imply that the survivors were well adapted to it.
Bottlenecks just have to be survived
by the fittest of the bottleneck,
but now we are after the bottleneck.
That doesn't mean that the ability to digest a nut was lost,does it?
After each ice age there was a worm age with different challenges
and selection on digestion and other abilities.
We know, that we are intermixed too with human traits comeing
from wormer areas- at least from irak area, possibly from africa
(in the wormer area much more humans will have survived).
So much on the ice age bottleneck,
but "we" also had a cereal eating bottleneck from about
4600 BC to 1900 AD. This is samelike in parts a new
kind of nutrition (much cereals instead of roots or whatever).
Same as for meat (new in such a high part IMO) applies to
cereals (too new in such a high part IMO).
I think humans are generally a very versatile species, with
the speciality to be able to cope with a very broad range of
nutrition.
I can see that some very recent changes in nutritions
(since industrial time and after WW II 4 generations) now completely
changed the situation again.
So much sugars and carbohydrates
without the necessary thiamin and other vitamins.
Thats totally new since *all* generations.
Loss of ancient detoxifying techniques as long germinated bread
(e.g. sourdough).
Thanks for the exchange of ideas on evolution
(also in the other "gene" thread)
Merry christmas.
Or birth of light or solstice if you want :-)
regards
Amadeus S.
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