Tuesday, December 4, 2012

Human sexual evolution


If I've never written something that made you feel awkward, this probably will. Read at your own risk.

Our biology reveals fascinating evidence of our
evolutionary history, and answers some interesting questions. Why are our penises so big? Why is the vagina so acidic? Why do we have sex so often per childbirth? Why so much pumping action, and why do females have a tendency to vocalize during sex? Why do we have large external testees hanging off our bodies? Any man can vouch to the inconvenience of his balls: they're terribly sensitive and present an easy target in a fight. It doesn't have to be that way. Gorillas have tiny 1-inch penises and balls safely inside their bodies. The answer to these questions is that sperm competition has played a prominent role in our sexual evolution.

The reason we have large penises is that a vacuum is created by the tight seal between the vagina and the penis. By pumping, the male can suck out any semen that may have been left by a previous male. His large external testees create enough sperm to allow him to attempt to fertilize many women each day. The female's vagina has barriers to entry, such as its acidity, so that only the healthiest sperm could fertilize her egg. Her tendency to vocalize during sex may be an invitation for other males to have sex with her as well.

I'm not saying that we shouldn't be monogamous, but I am saying that for the last several hundred thousand years, our species has not usually been monogamous. Some of these explanations may turn out to be wrong, but I think it's clear that evolution offers very plausible explanations of our biological characteristics, whereas the hypothesis that we are a special creation of a loving deity who wishes us to be monogamous does not offer plausible explanations of those characteristics. I think this evidence indicates that we are a product of evolution.

11 comments:

mostlyprobably said...

You and Sarah must have SO much fun.

And yes, I did feel awkward. You have made me feel awkward before, but this probably tops it.

Bennion said...

Well, I hope you found it interesting, as well as awkward ;)

gavinomics said...

I think the part about penises is a bit of a stretch. ("Wah Waaah")

Although I believe in evolution (http://qr.ae/1I6Au) I don't think that these explanations provide evidence for evolution. I think at best, you could only say the following about them, "Here are some phenomenon about human sexuality...and here is how one might explain them according to the theory of natural selection."

Also, I can't tell if the loving deity comment is more of a non sequitor or a straw man.

gavinomics said...

That "Wah Waah" was supposed to be the lame joke sound effect btw.

Bennion said...

I found your lame joke sound effect funny :)

The part of the loving God is meant to imply that if God loves us, and wanted us to be monogamous, he would have made us differently (assuming we were a special creation). Evolution is a better explanation of the evidence, imho. Of course none of this precludes the possibility of a hybrid explanation that involves evolution and God.

mostlyprobably said...

If this is evidence of evolution, why haven't gorillas' (to use your example) penises and testes evolved also? I think penises are so big because women's cervices are so long, I think the big penis and the big balls (I can't even believe I'm typing this!) are to increase a man's ability to reproduce more surviving offspring.

Ducks will often steal other ducks' babies right from their nest and "adopt" them so they can make sure they have more surviving offspring than other ducks. If a mommy or daddy duck dies, other ducks will steal the young of the dead parents for the same reason. I just realized that kind of went off topic. Sorry. Not.

Maybe big penises are due to evolution, but maybe they're just lots more fun that way. Or maybe, like the duck situation, they're just God's way of making sure that we're not stealing other people's babies from their dead parents. ;)

Bennion said...

It's because Gorillas haven't had sperm competition in their evolutionary history. They fight for the females and then protect them from other males, so large penises aren't necessary. Same with gibbons: gibbons are naturally monogamous, so they only mate once a year, because that's all that's necessary. I'm saying that our biology and behavior indicates we aren't a naturally monogamous species.

I'm a bit confused by the duck example though... it seems like a stolen baby doesn't count as your own offspring, so it would be counterproductive to steal other ducks' babies. The goal is supposedly to ensure your genetic material is passed on, so that's interesting...



gavinomics said...

The argument about God not loving us because he didn't make us monogamous is probably the worst argument I have read on this blog.
That's like saying that if God really loved us, he would have designed us to only like healthy food, or to never be tempted to sin, or to never become an atheist.

I could (I think more convincingly) make an argument that God loved us so much that he designed us to have strong sexual urges so that our ancestors would survive. Or I could say that God loves us so much that he gives us commandments that will help us to avoid the negative consequences of our polyamorous inclinations.

Regardless, I don't think that God "designed" us in that manner anyway. Even if he did, he couldn't subvert the laws of nature anyway, which means that he would have chosen the best trade-offs within the constraints of reality.

mostlyprobably said...

Maybe ducks, like humans, still consider adopted or kidnapped babies their own? It never really made sense to me, but it happens. That's why you see ducks sometimes with 15 babies following it.

Bennion said...

I guess so. Maybe they have a natural urge to raise children that is generally helpful, but occasionally is misdirected. That is pretty amusing though, and is pretty cute ;)

Bennion said...

I think you're skipping over the "special creation" part. I'm not arguing that these attributes mean that a loving God doesn't exist, I'm saying that if God made us from scratch, only a few thousand years ago, he would have designed us differently. And yes, I think it could be generalized to other attributes as well. We have many attributes and physical features that only really helped us survive prior to the agricultural revolution (sometimes only millions of years ago). If Adam was the first man, and started with agriculture (as the Bible describes), then it doesn't make sense that we'd have those attributes.

I don't think our species would have died out if we were monogamous. Gibbons have survived. The neolithic agricultural revolution made it pretty easy for us to survive, so if we started with that, we wouldn't have needed our "polyamorous inclinations," much less adaptations suitable to sperm competition.

I think "explanations" of these attributes that don't involve a long history of mankind (at least hundreds of thousands of years) are pretty contrived.

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