About 15 of us trundled over to Harvard’s Science Center last night for
a talk by David Haig, a newly tenured biology professor. This is
part of Harvard’s flagship series of science lectures for
non-specialists. Haig was purporting to explain conflict within
an individual’s mind by showing that paternally-derived genes and
maternally-derived genes may have conflicting goals within the same
person. Haig’s age and physique would have led you to expect him
to use as an example of conflict a person who couldn’t decide between
golfing in North Carolina and visiting the grandchildren in
Sheboygan. Instead he said “Suppose that I am considering an act
of sexual infidelity…” and proceeded to work out the pluses and
minuses.
The rest of the talk covered father-daughter incest (the school radio
station has a Saturday morning country/bluegrass show called “Hillbilly
at Harvard” but Haig did not mention it). In theory the parts of
the daughter’s brain controlled by genes she inherited from her father
might be less opposed to incest than the parts of the brain controlled
by genes she inherited from her mother. But this presupposes that
warring genes can get hold of distinct parts of the brain, something
that nobody has demonstrated. And really how does dwelling at
such length on an example that is tied up with genetic propagation and
birth defects help us understand day-to-day indecision such as “should
I get a Big Mac or Chicken Selects?”
Haig showed some interesting slides of mouse embryos in which only
genes from males or only genes from females were cobbled together
inside one egg. It turns out that genes from a male are
responsible for the embryo making large demands on the mother’s womb
for nutrition, etc. It is currently very difficult to make a
viable baby with two moms or two dads (genetically). It seems
that genes are imprinted somehow with the sex of their previous owner
and the same genetic sequence will behave differently depending on
whether it came from a male mouse or a female mouse. Once all of
this is figured out we will be able to create human children from two
mothers fairly easily (since they already have the egg and the womb and
just need some DNA gluing and imprinting).
From an evolutionary point of view, it makes sense that the father’s genes in the daughter would “want” to commit incest with the father – the progeny of incestuous mating would have more of those genes than the progeny of exogenous mating, and producing more copies of yourself is the name of the game in evolution.
The same argument could be made that the father’s genes want him to commit incest with his daughter, or that the mother’s genes want her to commit incest with her son, or that the mother’s genes in her son want him to commit incest with her. Yet incestuous relationships are apparently fairly rare.
IIRC, Carl Sagan discusses how all primates have a strong aversion to incest in _Shadows of Lost Ancestors_. This mouse research can’t be directly applied to humans, for that reason.
rps: There would be no evolutionary advantage for a mother-son incest gene. The bottleneck for for a female’s reproductive success is usually getting adequate food/protection and not finding willing sex partners, as it is for males.
The only primates without strong aversion to incest are white humans living in rural Tennessee. What’s the evolutionary explanation for that?
I find it very gratifying, enervating, encouraging, to read posts and comments like this: people considering substantive questions with their brains.
Roof Vent