From: rich@netcom.com (Richard Poppen)
Subject: Evolutionary reason for homo/bisexuality?
Date: Tue, 07 Apr 92 05:13:24 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 

Recently I've found myself speculating on a question that,
surprisingly, I haven't seen discussed here:  What is the evolutionary
reason for homo- and bisexuality?

I am not asking "What causes homosexuality in an individual?"  That
question has an answer like "this gene right here" or "a level of
compound X above y ppm in the mother's bloodstream" or "a childhood
environment that has attributes A, B, and C," or some combination of
such answers.  It might be an interesting question (as might, say,
"what caused my brown eyes?" or "what caused my SO's talent for
learning languages?"), but it's not what I'm asking.

Rather, I'm asking about the tendency or capacity for homosexuality,
which is obviously present in some fraction of the human population.
(I am specifically _not_ talking about what activates that capacity.)
One can imagine a completely heterosexual (though more boring) human
species, one in which having sex with a motss would no more occur to
someone than would, oh, having sex with citrus fruits.  (A few people
might do it, but it wouldn't be a widespread behavior, obviously
intrinsic to many people's nature.)  So why is there homosexuality?
(I'm not going to keep saying "and bisexuality", since I'm really
talking about the existence of any significant homosexual behavior in
individuals, not about exclusive homosexuality.)

Our species spent has spent most of its time--most of the time from the
advent of H. sapiens to now--evolving in an environment in which traits
that impair the ability of their bearers to survive to reproductive
age, or to have a large number of offspring, tend to be selected
against.  On the face of it, it seems that homosexuality would be
selected against.  If you spend some significant part of your limited
sexual time and resources with motss, you won't have as many offspring;
the offspring that carry the capacity for homosexual behavior won't
have as many offspring; ...; and your genes will lose.

You might say that homosexuality is just part of the human makeup.  But
it's not obvious that it's an inseparable part of it.  If it is
separable--if not everyone carries it, and it isn't linked to anything
else that's important--it can be selected away.

But that doesn't seem to be what's happened.  Homosexuality was around
at the beginning of recorded history, when having lots of offspring was
still important.  (Indeed, it still is, for the survival of your genes;
just not for the survival of the species.)  So the capacity to be
homosexual must have some indirect (i.e., not just reproductive)
evolutionary advantage, or be linked to some other trait with an
evolutionary advantage.  (For example, it could be in some way like the
gene for sickle-cell anemia, which also increases resistance to
malaria.)

Does anyone know of any actual research related to this, or have any
speculations?  Some of my speculations, without any scientific
justification:

* A clan with some adult non-parents fares better because they tend to
act as "parents-at-large", being able to work more for the clan's
benefit rather than in a more narrowly defined family unit's benefit.

* Altruism is a behavior that helps a clan.  People are somewhat more
likely to exhibit altruistic behavior toward those to whom they are
sexually attracted; bisexual inclination therefore helps activate
altruism.

* A tendency to homosexuality is linked with a higher sex drive in
general, leading bisexual males to have more offspring than strictly
heterosexual males.

* Sexuality cements pair-bonding, which is of great survival value, and
the presence of homo- and bisexual people allows a clan to pair up more
effectively when one sex is depleted for some reason.  Thus when male
M1 and female F1 have children, and (say) M1 dies, and F1 pairs up with
female F2, F1's ability to have a motss partner helps her existing
offspring survive.

* A tendency to homo/bisexuality is inseparably linked to intelligence.
(I like this one. :-)

Any comments?

--Rich

(Btw, can one hope that anyone who would jump in exclaiming that
homosexuality is unnatural, though it _obviously_ occurs in [human]
nature, won't believe in evolution either?)
Newsgroups: soc.motss