I doubt I need to convince any of this blog’s limited audience of the vacuousness of the bigot’s cry that homosexuality is “not natural”. There’s a post circulating on facebook that says something like “Homosexuality has been observed in 84 species, homophobia in one. Who’s unnatural now?”
However, while most people likely to read a blog on science would be opposed to bigotry against same-sex sex other forms of prejudice are more acceptable. By her own admission my friend Liz Conor over-generalised in her recent article in The Age about how humans are not really suited to long term monogamy, but the furious responses are indicative of how resistant many people remain to the idea there might be viable alternatives to monogamy (particularly ones that don’t involve men having mistresses but women being expected to be monogomous, because that’s how gorillas do it so it must be “natural”).
Now let me be clear, one needs to be very careful of the crude socio-biological view that human behaviour has a purely evolutionary basis and we can simply extrapolate from animals to justify everything some humans do. There is so much complex social and cultural interaction built upon human’s biological background that being too simplistic about our actions can be a betrayal of our capacity. It matters not at all whether what male mallard ducks do to females (to quote one famous example) can be considered rape – rape in humans is not justified one iota.
Nevertheless, I think there is some significance in the extent to which sexual behaviour deemed “unnatural” and “kinky” in humans turns up remarkably often in animals. Evolutionary biologists are still struggling to explain why homosexual behaviour is so common, but it is. Some other forms of “kink”, such as group sex in garter snakes or transvestism in cuttlefish have obvious explanations, but the causes of bondage amongst redback spiders is, as far as I am aware, unexplained. (I am willing to tell each of these stories in detail if requested in comments but I’m not spilling them unrequested – I’ve got to keep something for parties).
I was prompted to write about this by a story I’m working on for Australian Science. The eclectus parrot has been discovered to be only the third species, after humans and antichinuses, to engage in sex selective infanticide. As the scientist researching this notes, “infanticide itself is weird”. Nevertheless some species do go to the trouble of giving birth to young only to kill them, but only in these three cases does there seem to be a process where one sex or the other is killed, but not both. The antichinus situation is a bit hazy*, but with the parrots we now seem to understand the evolutionary basis for the behaviour.
The eclectus parrot always lays two eggs, and the females grow faster, and are able to leave the nest earlier. Unlike most bird species the sex is visible from hatching, and a mother with a poor nesting site, and therefore low prospects of raising her young to independence, may have better odds if she concentrates all her energies on a female rather than dividing it between both hatchlings if she happens to produce one of each. Instead of letting the male starve and being troubled by its cries, she will kill it soon after birth. Mothers with better nesting sites will raise both young, as will mothers that lay two male or two female eggs.
These actions make evolutionary sense, as long as so many parrots don’t have bad nests that the population becomes skewed with too many females. The same cannot be said for sex-selective infanticide in humans. The cultural undervaluing of girls that leads to this appalling practice makes no evolutionary sense so, fascinating as the parrot may be, it doesn’t tell us much about ourselves.
At least in regard to the infanticide. The parrot has another unusual characteristic however. It engages in polyandry, where the female has multiple mates but the male is largely monogamous. Amongst vertebrates this is relatively rare, but I wonder whether researcher bias may not have made it seem rarer than it is. The parrots practise it because nesting sites, even bad ones, are so rare. A female with a nesting site is in a position to take what she wants, and if that is four mates she can often get it. All her mates will provide her with food while she guards the eggs and hatchlings, even though some of them are not the fathers. Presumably they don’t know which of her harem fathered the young, and paternity tests indicate that if a male hangs around long enough he will usually get to father at least one offspring. I wouldn’t want to jump to any human parallels here, but it should certainly give pause to those who think male promiscuity and female monogamy is ordained by genetics.
In a similar vein I came across a recent media release explaining how polyandry can benefit female mice. It seems that when Minnie has sex with many Mickeys her male offspring have healthier sperm. This hardly proves such is the best route for humans given the complex emotional factors we deal with, but maybe the men who aggressively posted on Liz’s article about the disastrous consequences for children of “mum bringing home boyfriends” should take a look. (Although I suspect this is exactly what they are worried about.)
I don’t suggest we should all take our dating behaviour from any particular species, but one thing a survey of the biological world does indicate is that long term mutual monogamy is pretty rare. That doesn’t mean people should just give up on it, if that is what they want. However, anyone expecting it to be automatically better, let alone easy, needs to justify their case. Judging by the responses to Liz, they’re a long way from that.
*And frankly antichinuses have such a bizarre sex life anyway, who knows what is going on?