Differences between females and males

What statistical differences, in body and behavior, does science predict we might observe between females and males of the same species?

It’s not a safe topic for casual conversation, but it’s one that I think is interesting. I’ll consider whether it’s plausible that such differences might exist, and if so, why. I’ll try to keep this short and oversimplified — I’m not trying to write a book report on The Selfish Gene.

This is going to be about animal species that reproduce in a manner similar to humans. That is, those with a long gestation period, and who give birth to a small number of offspring at a time. I’ll also kind of assume that not all members of the species are perfectly monogamous.

Humans themselves might, or might not, be a special case. They are exceptional for a number of reasons.

This is only about statistical averages, and says nothing about a given individual. I suspect it’s challenging for evolution to fine-tune a brain’s high level desires in a way that is gender-specific. We shouldn’t expect perfectly predictable results.

Standard disclaimers apply. Just because I argue that something might be true, does not mean that I think it is a good thing. And it doesn’t mean I would promote any particular policy as a consequence of it.

Definition of female and male

Scientifically, the distinction between females and males is that the females have the larger and more robust sex cells. The female’s “egg” cell contains almost everything it needs to develop into a new organism. The male’s “sperm” cell, on the other hand, is stripped down to the point where it contains little more than genetic material, and whatever is needed to deliver it to the egg.

But as an explanation of differences in behavior, that’s too indirect. The important difference (I claim) between females and males is that the female possesses the limiting factor in reproduction: wombspace.

Sperm cells are cheap and plentiful. And while egg cells are more expensive to produce, they are not in short supply either. Wombspace is the bottleneck, so it is the most important thing you must gain control of in order to successfully reproduce.

Therefore, being in control of this all-important resource, the females get to make the rules, and force the males to do their bidding.

Except… that does not happen. At least, not in all species of this type. To understand why that might be, we should think about optimal reproductive strategies. And when necessary, we should look at it from the standpoint of the gene, instead of just the organism.

Reproductive strategies

To oversimplify it, a gene “wants” to get itself copied to the largest possible share of the bodies in future generations. It has some influence on how its current body develops and behaves. And that influence could be different depending on whether its current body is female, or male.

It’s complicated, of course. There are lots of different strategies that could work. It will depend on the environment, and the strategies employed by rival genes. But we can still try to predict the general sorts of things that are likely to happen.

One difference that we might expect between females and males is so obvious that it’s easy to overlook: We predict a tendency for males to be attracted to females, and for females to be attracted to males. I’ll go out on a limb and say that yes, this prediction is broadly consistent with observation. It’s not 100%, but it’s closer to 100% than just about any other behavior.

More about female strategy

If you’re female (or, a gene in a female body), you naturally possess wombspace. That’s nice; you are very likely to be able to use it to reproduce. The problem is that there is nothing you can do to increase your wombspace. You cannot employ other females to have your babies. At least, not unless your species has invented the technology to do that.

Optimal reproductive strategies for females might involve things like the following:

  • Place a high value on staying alive, and able to reproduce, for as long as possible. You should try to have the optimal body size, etc., for survival. You should try to avoid most risky behavior.
  • Make sure your children survive. You only get a certain number of them. And, unlike with males, you can be sure which ones are yours.
  • Ideally, mate with a high quality male. There are a number of qualities you might look for, but an important one is the ability to attract females. That way, your male offspring will themselves be more likely to reproduce. If you see a male who has attracted a lot of females, maybe that’s the male you want, even if you would otherwise not be attracted to him.

More about male strategy

If you’re male (or, a gene in a male body), you don’t automatically control any wombspace. But on the plus side, there’s no practical limit to how many children you can have.

But not every male can be a big winner. Under normal conditions, the mean average number of children for males and females in your generation must be about equal. (This is simply because every child has one mother and one father.) For every male who has a large number of children, there must be several males who have very few.

We can predict that this leads to competition: males competing, especially against each other, for a bigger share of their generation’s wombspace.

Optimal reproductive strategies for males might involve things like the following:

  • Do whatever it takes to win access to a wombspace. Basically, shower the world with your sperm.
  • If females like it when you do a silly dance, or sing them a song, or bring them shiny rocks, or do well in a contest, you should do that. It doesn’t have to make any logical sense.
  • Develop a body that is attractive to females, and able to do the things that females like.
  • Do these things even if they are somewhat detrimental to your ability to survive. Be willing to take calculated risks. The goal is to have the most babies in your lifetime, not to have the longest lifetime.
  • Pursuing other females might be a more effective use of your time than caring for your pregnant mate, or helping to raise children (which you can’t even be sure are yours). It depends on, among other things, whether a female of your species is likely to successfully raise children by herself. The uncomfortable truth is that in over 90% of mammal species, the males play no role in child rearing.

Closing thoughts

The tragic irony is that females don’t rule over males mainly because there is not sufficient evolutionary benefit for them to do so. They have the power, but they don’t have the motive to use it. Males have less power to rule over females, but are motivated to do so.

In humans, a somewhat uncomfortable possibility is that some of the pointless activities that males learned to enjoy doing in order to attract females, turned out to have significant practical value in the modern world, purely by chance. Keep in mind that humans did not evolve in the modern world — it hasn’t been around long enough.

It would already be technologically possible for a powerful human woman to transcend the limits of her wombspace, by employing an army of surrogate mothers. And someday, we might have artificial wombs. It’s amusing to think that, over evolutionary time, these things could change the equation enough that almost nothing I’ve discussed would apply to humans. But that’s just a wild thought, and time isn’t the only obstacle in the way of it happening.

So, that’s a quick overview of why I’m skeptical of the idea that females and males should, statistically, be pretty much exactly the same. It also explains why males are so much prettier than females, and why menopause doesn’t exist. So, I guess there might still be a wrinkle or two to iron out.

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