Nothing says Valentine’s Day like a pair of happy gibbons!
Among the apes, gibbons are the best representatives of true love.
Gibbons are unique among all our nearest kin in that they are monogamous (or nearly so, anyway). Although we are gradually learning more about the variety of social behavior seen in wild primates, same-sex adult gibbons generally do not tolerate each other’s close presence.
That makes it difficult for gibbons to live in groups larger than a nuclear family, with mom and dad and their immature offspring. Occasionally we hear of attempts in captivity to put same-sex adult gibbons together (say, in a zoo exhibit), but this usually leads to fighting.
Among anthropologists, the theory is that you can deduce something about the mating system of a primate species by looking at the degree of sexual dimorphism (the physical differences between the sexes). The general idea is that if males have to compete with each other for access to mates, they will have evolved to be larger than females. This is the case in gorillas, for instance, where the males compete to be the one silverback who gets to mate with all the females in his group. Gorilla males are about twice the size of females.
But in gibbons, males and females are about the same body size and are both equipped with fierce-looking canines. In the wild, they are territorial, and both males and females are involved in defense of their home turf.
Here at the IPPL sanctuary, we are fortunate to have many loving gibbon couples. (Though, between you and me, Jade has been known to give the glad eye to neighboring males on occasion, despite the fact that her long-suffering mate Palu-Palu is a totally adorable little fellow….)
It’s so sweet to watch a pair of gibbons groom or gently play-wrestle together. Valentine’s Day, or any day!
I routinely forget to count gibbons among primates, i.e. among our closest biological and evolutionary cousins. I do wonder, however, about the dimorphism business you mention in the article above: while it’s true that both bonobos and gibbons show the least dimorphic tendencies among the primates, it may well be that we, the human species, can overcome the biological compulsions of male competitiveness without necessarily having to evolve physically into less and less dimorphic differences between the sexes.
This, of course, is highly speculative on my part, but I do note that the rise of feminism (an extension of democracy) did not have to wait for the disappearance of dimorphism in our species — or even for its significant abatement.
Moreover, if we look at our recent species history a little more carefully (at the period of the last 5,000 years, say), we can also find several documented instances of cultures in which women enjoyed a remarkable social parity with men despite the obvious physical dimorphism obtaining between the sexes. This can be deduced even from such Stone Age cultural materials as parts of the Old Testament and certain of the poetic literature included and preserved by Judaism which predate it by a 1000 years or more. Similar examples of male-female near parity in social status were observed by ancient Romans among the Teutonic tribes they encountered on the territories of present-day Germany, and are documented for pre- and early-Christian Celtic Ireland, too.
This leads me to conclude that cultural evolution is a real phenomenon and that it can over-ride what we tend to think of as the “dictates” of our phylogenetic evolutionary heritage.
Yes, when I was an anthropology student years ago, gibbons were given short shrift, in favor of moving on to a consideration of more “interesting” apes (chimps, gorillas…). The whole sexual dimorphism issue is an interesting one. It seems that, among primates, the degree of sex differences in things like body size and canine size correlates with male-male competition (if males have to compete with other males for access to females, they will get bigger relative to females). There are likely other factors involved, too, like whether food resources are clumped (i.e., they can be defended by a big guy, who then becomes attractive to females wanting to eat from “his” fig tree…) or dispersed evenly across the environment (i.e., no point in fighting over food items like leaves, so there’s no advantage to getting bigger). If we assume that for most of our evolutionary history humans were subject to similar forces, it looks like our degree of sexual dimorphism is correlated with a “mildly polygynous” (not monogamous) mating system. That’s from a strictly biological viewpoint. Of course, as you say, anthropological and other data show that humans exhibit a variety of mating systems, including polyandry (in Tibet and elsewhere: http://www.theatlantic.com/health/archive/2013/02/when-taking-multiple-husbands-makes-sense/272726/). Interesting subject!