Have you ever heard of the New Mexico whiptail? Probably not. Well, the New Mexico whiptail is the only animal species – that I know – whose members all have the same gender: all New Mexico whiptails are female. There is no need for mating with male New Mexico whiptails in order for the females to lay eggs, which is a good thing since there are no male New Mexico whiptails. This made me wonder: why are there so few species having only one gender? Why do we human beings, and so many other animals, need two ‘versions’ of our species in order to prevent ourselves from extinction? Why not three or four? Is this number utterly random? Or might there be some reason behind it?

Before thinking about this question, I saw absolutely no reason for there to be this dichotomy of men and women ruling the animal kingdom. I always thought to myself, ‘Why can’t there just be one “type” of human – which we could then simply call “human” – that, just like the whiptails, gives birth every now and then, without requiring any “intervention” of a different sex? What would be wrong with that?’

Maybe it’s inadequate to ask whether it is ‘right or wrong’ for there to be both men and women. Nature, after all, doesn’t seem to care much about being morally right or wrong. Why else would it give AIDS to babies, who have done absolutely no harm to this world of ours? It is more likely that – assuming there is a reason explanation – there is a biological explanation for there the widespread division between men and women.

So let’s see: what could be nature’s ‘purpose’ in making two types of human? How could that ever be beneficial for so many animal species – including our own? Well, the distinction could be nothing more than a very fundamental evolutionary developed instance of Adam Smith‘s idea of division of labor. A division that appeared to be working so well that nature extinguished almost all species not conforming to this division. However, for this evolutionary explanation to be true, it would have to be the case that men and women together should be able to achieve more than only men or only women could ever do. Let’s take a look at that.

One could claim that a division of labor in which the woman carries the baby and the man gathers food (for the woman, the baby and himself) could benefit the reproduction chances of both the woman and the man. Because think about it: chasing swine while being pregnant does not seem to be very convenient. In this case, having the woman at home – safely warming herself at the fire – and having the man out hunting – not having to worry about endangering the life of his unborn child – could be a set-up benefiting both parties.

Another explanation could be that the existence of both men and women provides both parties with some sort of purpose in life: the purpose to form little groups, called ‘families’, thereby creating structure into – what otherwise might have been – chaos in the animal kingdom, or an utterly meaningless life; a structure that would make every creature better of. Because, again, think about it: what would the world be like in case there was only one type of purposeless creature wandering around? Wouldn’t that lead to an utterly unstructured and – therefore – unsafe environment? The families that provide the confines in which each one of us can life relatively safe have fallen away.

If that would indeed be the case, it might have been evolutionary beneficial for our species to ‘develop’ the distinction between men and women; simply in order to program the species members with a goal: to create that save little world they can call ‘my family’.

However, none of these explanations explains why there are only two sexes; maybe humanity would be even more organized – and even better off – if there were three, four or even more sexes. So why only two? Well, maybe nature ‘decided’ to go for only two because creating more than two might have complicated things a little too much. Now it’s at least clear what everyone has got to do: find a man or a woman, make a family, and live happily ever after.

But what do you think?