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bolwerk's avatar

Do you agree that sperm competition might be a vector for natural selection?

Asked by bolwerk (10312points) December 17th, 2010

Sperm competition, or sperm warfare, posits that different males’ individual spermatozoa compete (kind of like sperm armies) inside of a female for the opportunity to fertilize an ovum. Many variations on the theory exist, but common themes discussed include the biological imperative of male and/or female promiscuity, functional differentiation between spermatozoa (e.g., being able to block another spermatozoon from fertilizing an egg), carefully primed ejaculates depending on the type sexual encounter or partner involved, and the possibility that sperm competition makes it possible for human beings to behave cooperatively while competing sexually. What do you think? If some variation of the concept of sperm competition is true, what ramifications does it have for sexual ethics?

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15 Answers

crisw's avatar

Absolutely I agree that sperm competition is selected for. A recent book that covers this in great detail, which I just started reading, is Sex at Dawn.

The biggest ramification it has for sexual ethics is that it’s one more piece in the puzzle that tells us that humans are probably not as evolutionarily monogamous as many like to think we are.

MissAnthrope's avatar

I do agree.. or at least, that is how the evidence stacks up at this point. I will say that I find this evidence and the idea of sperm competition to be pretty convincing. It just makes a lot of sense. Consider that monogamy is not the default in nature and that it appears that while humans have developed social constructs around fidelity to one mate, our biology tells a different story. I’m guessing that promiscuity, to any degree, was beneficial to the human population when the survival of the species was anything but guaranteed. The biggest positives to non-monogamy are increased genetic diversity (a must, if a species is to survive) and, of course, increasing the chances/occasions of impregnation (population increase).

I don’t think our sexual ethics are going to change detrimentally. We may have to relax a little bit and admit that we’re fighting our biology when it comes to monogamy and fidelity, maybe become more accepting of alternate relationship types, such as polyamory and open relationships. Personally, once I realized that monogamy is not quite human nature as we like to think, I grew to accept alternative types of sexual relationships. I mean, these may not be mainstream, but those who practice it are aware that monogamy goes against their natures, and I rather like that self-awareness and honesty.

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crisw's avatar


Actually, you can figure some of this out just by having sex :>)

There’s a reason that human males have such big testicles, for example. And it isn’t just to make porn films.

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Simone_De_Beauvoir's avatar

It’s a leap to make connections between how sperm behave and sexual ethics – these are disparate in degree and in ramifications. I always found the language surrounding how sperm and ova interact to be telling because it consists of so many qualifying words that are better suited to describe actual human interaction rather than ‘actions’ of parts of humans. The notion that ‘sperm do all the work’ to get into this ‘passive ovum’ is linguistically biased. You can see a different perspective here.

bolwerk's avatar

@Simone_De_Beauvoir: considering ethnics in light of how we evolved isn’t such a leap, however.

bolwerk's avatar

@Simone_De_Beauvoir: what’s to elaborate on? Evolved sexual behavior, the kind surrounding theories about sperm competition, certainly relates back to sexual ethics. I asked the question looking for other people’s thoughts on the matter.

Simone_De_Beauvoir's avatar

@bolwerk Well, it is then my thought on the matter is that it can be argued that societal ethics (a human construct) are not brought (and do not bring) about by minute biological processes like selection for sperm that is more ‘competitive’. We can talk about selection for specific kind of sperm – cool subject, btw. I am simply having trouble understanding how we can jump from discussing competing sperm to human promiscuity or partner choice. Do you have any ideas on how the relationship flows…in that, what is the direction of effect of one on another? Evolution on a biological level occurs many times slower than any chances in social norms or sexual norms – I don’t think our sexual ethics (which change decade by decade) affect selection for competitive sperm over hundreds of years.

bolwerk's avatar

@Simone_De_Beauvoir: maybe this wasn’t clear from the short description (I didn’t feel like writing a novel), but it’s not the behavior of the sperm that I was talking about that brings up ethical questions. Generally sperm competition refers to a wide range of theories and biological possibilities, and maybe in some cases they don’t have much to do with macroscropic human behavior. Nonetheless, in most cases, they challenge traditional assumptions about sexual behavior – and such challenges must come with ethical ramifications, at least for human sexuality, if only to ask if what we do now works.

To answer your question, I would guess usually the behavior of sperm in sperm competition follows from certain types of human behavior – behavior humans evolved, obviously unconsciously, to deal with (whether consciously or unconsciously). The degree to which the behaviors surrounding theories of sperm competition are relevant, conscious, advantageous, and/or ethical are clearly debatable.

I think you’re right that biological evolution is a slow process, but behavioral evolution could be faster. It doesn’t take long for a group engaged in a counterproductive behavior long to wipe itself out – and there’s nothing that says such a counterproductive behavior couldn’t have been productive for previous generations. And then there’s the whole matter that humans are likely capable of a whole range of behaviors, and social circumstances trigger them – the whole nature v. nurture debate.

crisw's avatar

“I am simply having trouble understanding how we can jump from discussing competing sperm to human promiscuity or partner choice.”

Well, the way that I look at it is that there are clues in our biology as to what sexual patterns our ancestors followed, Not that this constrains us to follow those patterns- but it helps explain some things.

Human males have, compared to many other mammals, huge testicles and produce a lot of ejaculate. Most human males are also turned on by watching others having sex, and a very common fantasy- and practice- is one woman having multiple partners.

In other mammals, this behavior accompanies non-monogamous mating systems where one female may mate with many males. Sperm competition is most common in such situations.

I don’t think this has any bearing on telling any one person what their sexual ethics should be. But it is a great argument against those who claim that humans have always been and should always be monogamous. Sperm competition, along with many other biological facts, disproves such claims.

Simone_De_Beauvoir's avatar

@crisw Yeah, I don’t get when people try to explain monogamy using biology or ‘other animals’ either, :)

bolwerk's avatar

Monogamy is sometimes observed in other animals. Of course, the messed up part is that animal sexuality is probably radically altered by human contact, like a biological Heisenberg paradox.

For that matter, it’s a perfectly common, effective, and legitimate sexual strategy in humans. The shocker for some people is, it’s just one of many.

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