I find it funny when conservative politicians and religious leaders attempt to categorise human sexual preferences, gender roles, relationships or parenting arrangements as 'natural' or 'unnatural'. Anyone who appeals to the natural world to justify their own position on human morality clearly doesn't know much about nature. It's likely that when such people think of nature, they form a mental image that looks something like this picture:
Look at this wholesome, monogamous, nuclear swan family. Mum and dad swan form a lifelong pair bond, stake out a territory, and raise a brood of cygnets every breeding season. Admittedly, these are black swans, which might be off-putting for some conservative politicians, but you have to admit that all in all, it's a lovely sight.
Unfortunately, there are some animals in our community who don't share these good, solid swan values. I hope this isn't too shocking, but I'm about to show you a picture of some filthy, dirty sex.
Of course, if you're an earthworm, life in the humus layer means everything you do is filthy and dirty. But, as you can see, the two mating worms are joined at two points. This is because earthworms are hermaphrodites. They mate by matching their male and female organs in a complementary fashion. It's thought that the evolutionary reason for this is that producing both sperm and eggs allows the worms to maximise their reproductive output in an environment in which it might be difficult to meet other worms. After mating, the worms move on and will probably never see each other again. Put simply, worms are promiscuous lady-boys who like it both ways because this gets them twice the amount of sex. And, being hermaphrodites, they become both single mothers and absent fathers at the same time.
You might think it's ridiculous to expect invertebrates to stick to good old fashioned values like monogamy. But some invertebrates manage it. Bonellia viridis is a marine invertebrate from a relatively obscure phylum known as Echiura. Members of this species are either male or female, and form lasting, monogamous pairings. If simple marine creatures can manage this, why is it so difficult for a complex primate like a human being? If only we could become more like Bonellia, the world would be a better place.
Yes, if we were more like Bonellia, a woman of marriagable age would lie in wait until a baby boy drifted her way. Then she would swallow him and imprison him in her reproductive tract, feeding him off her bodily fluids until he matured and began to pump out sperm on tap. This what happens in the Bonellia world. The female lies on the ocean floor until she meets with a tiny free-swimming larva. The larva is then sucked inside the female's feeding tube and remains as a parasite in her genital sac, with the sole purpose of sperm production, for the rest of his life. Yes, folks, there's no such thing as divorce in the Bonellia world. Those guys really know how to make a relationship last. What a great example to set for their larvae!
Some young animals are not so lucky. This lizard has two mummies. The desert-dwelling whiptail lizard (Cnemidophorus uniparens) is a species in which, as in a prison or boarding school, the entire population is female. This may seem like a sure way to go extinct. But, along with a few species of reptiles, fish and insects, these lizards have a special feature that allows them to survive. Whiptail lizards can reproduce by parthenogenesis, which means that they can lay eggs that hatch into young without being fertilised. While these lizards can become single parents, the chances of a female ovulating increase if she engages in ritual courtship behaviour with another female. This behaviour resembles that of related, non-parthenogenic lizards, and may include mounting. Then, after a female has laid her eggs, changes in her hormone levels cause her to behave like a male, and court another lizard who is pre-ovulatory.
With creatures like this in the world, it's nice to see that there are still animals like the Sand Tiger Shark (also known as the Grey Nurse Shark), who do it the old-fashioned way. No funny business there. Boy shark meets girl shark, then here come the little nippers! Just a normal family - Mum, Dad and a couple of extremely sharp-toothed embryos who devour each other in the womb. Ultimately, just one of the offspring is born, having grown big and strong on the flesh of his siblings.
One reason the natural world is a useless place to look for moral guidance is that animal behaviour is a result of evolution. The evolutionary process has no moral dimension, and represents only the triumph of superior function. And, on a more obvious level, virtually every human behaviour, from cooperation and maternal love to rape, infanticide, and cannibalism, are all technically natural to the extent that they have parallels in nature. American sex researcher James Weinreich has said that 'If animals do something we like, we call it natural. If they do what we don't like, we call it animalistic'.
But enough talk, because here comes our young swan family again. The cygnets will soon be growing adult plumage, finding mates, and raising young of their own. But what's this? Maybe only a mother would know, but one of the cygnets doesn't look at all like papa swan. Junior does, however, bear a striking resemblance to that handsome male swan from the couple in the next nest...
In the last few decades, advances in DNA sequencing have blown apart previous assumptions about bird mating systems. Now that the paternity of the offspring can be analysed, it has been shown that extra-pair matings are common in many species. One of my lecturers, who has a particular interest in adulterous birds, conducted a study and found that on average, 15% of cygnets in a black swan population were fathered by a male other than their mother's mate. An average of 38% of broods contained at least one illegitimate cygnet. It appears that the swans are putting up a veneer of respectability, while secretly acting just as they please. Which, if you're a conservative politician or religious leader, is probably something that comes very naturally indeed.