Human penis-shape and sperm competition

Form follows function.

I was more thinking that SUNY Albany was a really randy campus.

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Just wondering: What percentage of the students polled were women? And did they make sure there was agreement that ā€œhad sexā€ meant intercourse?

More seriously: The only way I can interpret the question so it makes sense (I presume they didnā€™t ask about a specific 24 hour timeslot!) is to add ā€œeverā€ to it. That being the case, Iā€™m not wholly surprised that 12% might have multiple bed-friends and on one occasion or another have been with two of them on successive nights.

Even more seriously: Without social norms ā€“ ie, over the time when homo sap was actually evolving current dimensions ā€“ can anyone actually doubt that this could occur?

Of course, demonstrating the effect does not actually mean itā€™s significant enough to have been selected for. It just means the theory hasnā€™t been disproven yet.

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ā€œThe human penis as a semen displacement deviceā€ or ā€œThe evolutionary advantage of sloppy secondsā€

So STDs are a retaliatory escalation?

Not in all cases. Some foreskins are long enough to partially cover the glans during erection- some are long enough to fully cover it, even during intercourse.

They are experimenting on sperm already present from a first intercourse which may in orgasm and uterine contractions.on the part on the female.

ā€œmayā€. Key word.

Which is true of this whole experiment. As I said, all this has done is demonstrate that the idea is not unreasonable, which is different from proving that itā€™s correct. Itā€™s suggestive (in multiple senses), not conclusive.

Remember, evolution is random events which find utility, not design. A particular characteristic, once acquired, wonā€™t be lost unless it is selected against, ā€œWhatā€™s it forā€ may be the wrong question unless thereā€™s a reason to believe it it should not be present.

Theyā€™re saying that contemporary behavior for optimum-age-of-high-fertility females is to have sex with multiple male partners within the insemination window, and thus it is possible to extrapolate back in time and surmise that evolution favored males with this type of penis shape.

Which this experiment does not confirm, but at least fails to refute. Itā€™s one small step (or poke) forward.

I think it was more the 12% number that had me confused. It doesnā€™t seem like a very big number.

12% of a random group of female college students admitting to multiple sexual partners within a 24-hour window seems low to you?

I must be older than I thought.

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No, that number seems about right to me. But it seems a like itā€™s a low number to be used as justification for leading to their evolutionary theory.

Thatā€™s certainly more than significant enough to effect evolution.

Evolution over millions of years is sensitive to tiny differences in an organismā€™s ability to create an offspring.

Think how tiny the effect of, say, eyebrows is. If we were guessing, Iā€™m sure weā€™d predict that not having eyebrows would affect the ability to create an offspring in far fewer than 12% of humans. You think that many people would get so much sweat in their eyes that theyā€™d all die before sex? Yet even if it gave an organism a 0.0001% improved odds at creating an offspring, it was enough to influence the evolution of humans.

youā€™re right, not in all cases. there are rare exceptions, but those are outliers in this context.

Well, I guess this is why Iā€™m not an evolutionary biologist.

And also: the behaviour of modern-era late-teen-to-early-20-somethings seems like a poor justification for an evolutionary theory. Since, for example, if you did the same survey 100 years ago, the numbers would have been MUCH different.

Thatā€™s fair enough, and might be true, but if you went back 100,000 years ago you might find that these results were just as true then.

Chimpanzees and other apes often have sex with multiple partners in a short period of time.

I think the point of the study was because, if itā€™s true now, then thereā€™s something in our hard-wiring that makes it at least acceptable ā€“ these college students arenā€™t recoiling in horror at the thought of multiple partners, unlike something weā€™re hardwire to think of as abhorrent, like sibling incest.

So thereā€™s good reason to think that our brains arenā€™t so different now than they have been in the past many many thousands of years, so early people probably werenā€™t that different. If we donā€™t find anything biologically abhorrent about the idea now, we probably didnā€™t then either.

But itā€™s certainly true that if they surveyed a bunch of Puritans 200 years ago, theyā€™d get quite different answers, and so might have drawn different conclusions. And, in general, all studies of US college freshmen (i.e. most psych studiesā€¦) should not immediately be taken as gospel truth for all of humanity.

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Bonobos more than most, and they seem to be our closest relatives. (They made the same adaptation we have of merging sex into their grooming behavior repertoire.)

Maybe itā€™s because Iā€™ve never had a sibling of opposite gender, but Iā€™ve always been skeptical about how much of that is hardwired vs. social. Preferring a non-sibling partner Iā€™ll believe. Abhorrent, I have trouble crediting; too much incest does occur despite the social bias against.

There is a known issue with people who lost contact with their biological families at birth or shortly thereafter growing up and then developing a strong sexual bond with someone who turns out to be a close biological relative. Itā€™s called genetic sexual attraction. They feel specially drawn to the person but they donā€™t realize itā€™s because theyā€™re family.

Some of these comments have me mystified. I donā€™t understand people who think that human behavioral study is prescriptive rather than descriptive. The evolution of our behavior and biology is consequential- but not really important.