The way they don’t do it on the Discovery Channel…
Reflecting on same-sex sexual behavior in animals other than ourselves.
Camille Longmore
Humans are, by far, not the first, nor the only ones, to be occasionally
attracted to the same sex. Homosexual behavior, such as same-sex courtship,
pair bonding and copulation, has been documented literally thousands of times
in a wide range of species spanning across taxa-- including mammals, birds,
reptiles, amphibians, insects, mollusks and nematodes (Bailey and Zuk, 2009). Researchers
have attempted to elucidate possible evolutionary origins of these behaviors, as
well as reasons for their maintenance in populations. Here, I will touch upon a few particularly intriguing examples of what’s been called an “apparent
paradox” that violates the basic “law of nature: that of procreation” (Levan et al., 2008).
Ok… this might be taking it one step further….
Same-sex behavior has been considered as a puzzle that requires a
special explanation, and can be compared to behaviors like suicide, or adoption
of unrelated infants, all of which don’t lend a direct fitness benefit to the
individuals who exhibit them. However, as a behavioral ecologist, I, personally,
am pretty hell-bent on finding one! I mean, look how it turned out for the
unicorns…
So why do these animals do
it? Homosexual behavior defies the long-held popular belief that all sexual
behavior in animals is somehow linked to reproduction. However, a look at a particularly
promiscuous species, the Bonobo monkey, offers other possible explanations.
Sex in Bonobo monkey
societies is, essentially, a free-for-all. Female bonobos only actually
reproduce every six years or so, yet they have sex... all the time… no matter
if they are pregnant, nursing, very old or very young (Fruth and Hohmann,
2006). Because sex in none of these fours states will yield reproduction, there must
be some other advantage to such nymphomanism. Furthermore, they do not restrict
themselves to heterosexual activities; females are often found to engage in
such behavior as rubbing each other’s genitals (sometimes even successfully…),
while males kiss, touch and hump each other to a lesser extent, but frequent
nonetheless. Bonobo sex is so prolific (to the extent where it dominates the
species’ ethogram, or list of behaviors of a species), it trumps other behaviors
such as fighting, and the apes have been dubbed the “Make Love, Not War”
primate species. In fact, researchers Fruth and Hohmann hypothesize that sexual
behavior might ease social tensions in a hierarchical society such as theirs,
as well as facilitate reconciliation among group members that may have had a
spat. I think our species may have something to learn from them…
While a fascinating
overview of homosexuality in several species, skip to 5:30 for the ultra-sexy
story of Bonobos.
Like the majority of
bonobos, parthenogenetic whiptail lizards seem to enjoy “meaningless” sex. As a
parthenogenetic species, a female needs no male in her life in order to
reproduce; her eggs require no fertilization in order to develop. This is surely another example of homosexual behavior lending no direct reproductive benefit…
or is it? Studies have found that the females that engage in copulation
behavior have more, as well as better quality, eggs than females who didn’t
(Crews and Fitzgerald, 1980). Mating behavior,
if not actual mating, essentially stimulated good egg production. Now that’s
good reason to dry hump!
Animalsrightsadvocates.org
These frisky
reptiles, while appearing to be engaged in a successful copulation, are, in
fact, two females.
Another example of animal
homosexuality is a touching one. In the Laysan albatross, long-term pairing of
unrelated females (ruling out possible kin selection motivation where a female
is at least gaining from passing on her genes via related kin) has been well
documented (Young et al., 2008). In
this case, there is an uneven (female bias) sex ratio in the species, so pairing
up with another female to raise offspring is better than not pairing up at all,
and fledging no offspring. In fact, both females in the pair were linked
genetically to at least one of their mutual young, so both were gaining (fitness
wise), by this behavior. Furthermore, same-sex pairing removes excess females from the
population that would, under other circumstances, provide pressure for males in
opposite-sex pairs to abandon their partner (Young et al., 2008); the same-sex females
might essentially be “taking one for the team” for the greater benefit of their
species!
www.chacha.com
Same-sex
“lovebirds”
Bailey and Zuk, 2009
I’d like to end with a
little bit of “food for thought”… while homosexuality is found in over 150
species, homophobia has been found in only one. Homophobia, not homosexuality, may
be, then, what is not adaptive!
Literature Cited
Bailey, N.W., M. Zuk. 2009.
Same-sex sexual behavior and evolution. Trends in Ecology and Evolution 24(8):
439-446.
Crews, D., K.T. Fitzgerald.
1980. “Sexual” behavior in parthenogenetic lizards (Cnemidophorus). Proceedings
of the National Academy of Sciences 77(1) 499-502.
Fruth,
B. and G. Hohmann. 2006. Social grease for females? Same-sex genital contacts
in wild bonobos. Homosexual Behaviour in Animals, Cambridge University Press
294–315.
Levan, K.E., T.Y. Fedina, S.M. Lewis. 2008. Testing multiple hypotheses for the
maintenance of male homosexual copulatory behaviour in flour beetles. Journal
of Evolutionary Biology 22: 60–70.
Young, L.C., B.J. Zaun, E.A.
VanderWerf. 2008. Successful same-sex pairing in Laysan albatross. Biology
Letters 4: 323-325.
Very interesting Camille! I was not aware these interactions could provide direct fitness advantages (i.e. higher quality egg production in whiptails) - I wonder if these physiological changes might result from general well being.... (hormonal regulation perhaps?). Whatever makes you happy :)
ReplyDeleteAwesome Camille, especially your last sentence. It was very interesting to find potential benefits in the animal kingdom of something that "contradicts" the idea that the primary goal of sexual contact being for reproduction purposes only. A little old, but still one of my favorite videos:
ReplyDeletehttp://www.youtube.com/watch?feature=player_embedded&v=yMLZO-sObzQ#!