From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Thu Apr 04 2002 - 17:47:35 MST
On Thu, 4 Apr 2002, Wei Dai wrote:
> On Wed, Apr 03, 2002 at 07:38:43PM -0500, CurtAdams@aol.com wrote:
> > It wasn't a change in genes that caused the transition, but a change
> > in culture. However, the lower reproduction due to those
> > shift is going to be partly caused by pre-existing genes, (virtually
> > anything about humans has both genetic and cultural components) and
> > those genes now face huge negative selection pressure. When they
> > go away people will go back to having lots of babies.
>
> Any guesses what genes are casuing the lower reproduction?
>
My guess that if we have lower reproduction rates now its
primarily cultural and not genetic. People have more sexual
partners now so its much easier to contract a STD that makes
you less fertile or infertile.
In addition, the demographers and the Hunger Project have
shown that as you educate women, give them more control
over their fertility and the population as a whole becomes
wealthier, people simply choose to have fewer children.
In poorer countries where there is no national social
security or pension system, having many children is how
people guarantee that there is someone around to hunt
or grow food for them when they are less able to do so.
The social security systems transfer that responsibility
to the younger generation as a whole so individual families
can decrease the number of offspring they have. The only trend
against that is in cultures that may remain largely
agricultural and having extra hands around at planting
or harvesting time increases family income.
The standard line you get from biologists is there isn't
anything that has happened during the period that humans
have been civilized that could significantly alter the
natural gene pool. I suppose that we could speculate that
civilization has probably allowed the overall fraction
of deleterious genes to increase in the gene pool.
Obviously near-sighted people like moi make lousy
mammoth hunters. That might account for any reduced
natural fecundity.
Robert
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