Re: exogamy, kinship, and heterozygosity

Jim Kohl (
5 Oct 1996 03:27:50 GMT

In article <5315nu$>, says...

>The answer is given clearly by bacteria, who do reproduce asexually by
>fission; bacteria also exchange extra-chromosomal dna with each other,
>thereby engaging in a form of genetic transfer which has the same
>result as sexual reproduction: randomly combining genes with other
>organisms, gambling that the fitness of your descendants will be higher
>as a result.

There are bacterial strains that do not reproduce if their nutritional
environment is deficient in chemosensory stimuli that signal the
availability of food. There are yeast strains that are aided in genetic
transfer by a mating pheromone (that helps them stick together for the
exchange, when they happen to bump into a "sticky" potential mate).
Mammalian pheromones are chemosensory signals that assist in the mating
for genetic diversity scenario. Men and women have been trained to
distinguish between the odors of congenically bred mice that vary only at
the MHC locus.

>2. Humans have a pheromonically-mediated attraction for sex partners
>with high degrees of genetic distance; one obvious benefit of such a
>reaction is in the area of immune response. A higher degree of
>variability in immune response confers a better chance of surviving the
>next disease.

Several human studies indicate that women may mate for genetic diversity
on the basis of subtle odor cues (e.g., pheromones). The mechanisms
behind this type of choice remain to be detailed, yet are expected to be
largely chemosensory/olfactory, as they are in other mammals. Of interest
to others may be a forthcoming report that a synthetic human pheromone
(progesteronic) decreases luteinizing hormone/follicle stimulating
hormone pulsatility in men, and a recent presentation detailing an
increase in men's testosterone upon exposure to the synthesized ovulatory
pheromones of women.

It is beginning to appear that human incest avoidance is an olfactory
manifestation via the effects of chemosensory stimuli on levels of
reproductive hormones that _may_ influence properly timed reproductive
sexual behavior.

Jim Kohl