Comment on Evolutionarily speaking, wouldn't premature ejaculation be considered the desired trait?
memfree@piefed.social 12 hours ago
Several things to consider, but I'm not sure about the first:
- I half-remember something about the female response helping the sperm get to their destination, but someone else will need to figure out if I have that right. I'm more confident that there are claims that the head of the penis is shaped to pull any existing semen out such that repeated action would make it more likely that any previous encounter was at a disadvantage over the more recent mate. Since I didn't study this myself, I've no idea how valid those claims are, but I know research papers exist and include several other species as well as humans.
- Will premature ejaculation reduce pair-bonding? Will the female opt a different mate or no mate at all if she has no desire to repeat the encounter? The female might have one pregnancy with an unsatisfying partner and many offspring with someone else.
- Will the female keep the offspring? Historically and in many other mammals, a mother may reject her young. She might do this because she is alone and can't care for it, or has a different mate who rejects it.
- Will that offspring survive to reproductive age? If not, the initial preganancy doesn't matter because an abandoned/neglected baby or youth that fails to reach maturity is an evolutionary dead end.
Contramuffin@lemmy.world 7 hours ago
On the first point, I read the original paper. It was wild and shouldn’t be taken as fact. The authors modeled a 3d penis and vagina and showed that the penis is able to scoop out paste from the vagina. They then interpret it as that it’s “possible” for the penis to have evolved the way it has to scoop out rivals’ semen.
The obvious counter to the claim is that anything can be used as a shitty scooping spoon if you try hard enough.
Also, note that that woman would need to have some wild body counts if she’s having sex so often that she doesn’t even have the time to let the previous guy’s semen drip out
exasperation@lemmy.dbzer0.com 10 minutes ago
The starting point is the focus on ways in which human sexual behavior is different from those of our closest living relatives, other primates and apes, and how the observed sexual behavior of those other species correspond with physical characteristics in their genitals.
I found this paper to be pretty interesting, and it has a decent summary of why the semen pumping theory sticks around despite some pretty significant issues. It proposes its own theory for the glans penis, but the discussion of the history of the displacement theory is good background on its own.
Basically, species with low sperm competition (where each female tends to mate with only one male) have smaller testes and smaller sperm midpieces (the motor unit that actually drives movement), and species with high promiscuity and high sperm competition, like chimpanzees, tend to have larger testes and larger sperm midpieces. And on these metrics, humans sit towards the less promiscuous side of the spectrum.
So any theory of intense sperm competition is pretty inconsistent with other observed characteristics of human genitals and sperm.
But there also aren’t good alternative theories for human penis shape, when comparing all the primates that do or don’t have similar features.