It makes sense from a why standpoint. I can't help but wonder about the how.
How did we evolve reproductive organs that are not only sensitive, but also release reproductive cells at climax?
I'm ok with a "we have no idea" answer, but if there is an answer I also want to know.
I generally think this is true. And then I remember duck oviducts. Why does it need to be a corkscrew shape with little culs-de-sac for duck semen to die? For some reason it means that the female has more reproductive control when being forced or coerced during sex. But how that even works is beyond me. From a site with pictures and diagrams:
"As male ducks evolved longer, more elaborate phalluses, females countered with reproductive tracts that twist in the opposite direction, creating spiral pathways and blind pockets that make it difficult for unwanted sperm to reach the egg.
This anatomical design gives females a degree of reproductive control, allowing them to favor sperm from chosen partners while still protecting against fertilization from forced matings. Scientists studying this phenomenon have found that the more coercive the mating system in a duck species, the more complex the female’s reproductive tract tends to be."
Ducks which force themselves on a female duck are more likely to be undesirable to begin with. The ability to filter out the weaker genes, and choose a "better" mate would lead to better offspring survival. Particularly if the female is already eaten limited by egg production rates.
The opposite has occurred in a particular Beatle (who's name I have forgotten). They have a perfectly functioning reproductive system. However, the male ignores it and stabs them through the side.
It turns out, in related beatles, when a female is mortally wounded, they dump out eggs as fast as they can, before dying. This causes a selection pressure which wiped out normal reproduction.
Are you thinking of bed bugs? They don't dump their eggs, but have lower lifetime egg output because they are mitigating the attack. Seed beetles? Female gets injured, but the male's spines are linked to other traits that make her offspring do better. The net effect on her reproduction is actually positive despite the harm.
With ducks, the coercer quality hypothesis is an important hypothesis. But the evidence has caused the hypothesis terrain to shift to the indirect genetic benefit or reinforcement of existing preference hypothesis. Here's some situations that complicate the coercer quality hypothesis.
Coercers aren't reliably the "leftover" or inferior males as expect in the coercer quality hypothesis. It's mostly already-paired males doing the forcing, or, put another way, already screened and selected males which is arguably an indicator for genetic fitness.
If the tract exists to filter for good genes via female choice, you'd expect some positive relationship between choice-related investment and tract complexity. Instead, egg size (a proxy for female investment) is negatively correlated with both penis length and vaginal spiral count according to a 2020 study. This is the reverse of the prediction. Some in the research community argue female reproductive investment is doing more of the explanatory work. And not mate quality screening.
So the current leading hypothesis isn't "the tract detects and blocks bad genes," it's closer to "the tract protects a choice she already made through courtship, before force ever entered the picture." Coercion gets filtered because he isn't the one she picked. But this isn't settled yet and there are ongoing debate and more research to be done.
Yes, bed bugs are one species that does it: https://en.wikipedia.org/...
Probably because otherwise the females don't mate, or are killed during the mating or birthing process. Or it's possible that there are non-genetic factors to how they develop.
Anyway, I'm not a specialist in ducks, but unless you believe that a higher power is responsible for evolution, which I emphatically do not, based on the evidence, the mutations are relatively random and the only reason a very specific one ends up across an entire species is if the ones who didn't have it, died off, mated with the ones who did have it, and/or didn't have enough to opportunity reproduce.
So your first paragraph is a bit irksome.
Probably because otherwise the females don't mate, or are killed during the mating or birthing process. Or it's possible that there are non-genetic factors to how they develop.
Because it's speculation to preserve the three explanations for all evolved traits that you know about.
(1) easier to survive -> killed during the mating or birthing process
(2) easier/more survivable reproduction -> otherwise the females don't mate
(3) makes the mate more appealing so others want to mate with you.
Now hold the duck tract up against each one: Not (1). A corkscrew oviduct isn't a survival trait, it's purely reproductive plumbing. Not (3). It's not making anyone more appealing. It's not a peacock tail. Nobody's choosing a mate because of a more convoluted tract. Ipf anything it's invisible to mate choice entirely, it only matters after copulation. Not (2), and actually the opposite. The duck tract makes reproduction harder. It's a filter to block fertilization from certain partners.
And finally, we have enough evidence to show that this is a heritible trait. So what's going on?
This is called antagonistic coevolution. This is an evolved trait that makes it harder for all partners. The tract can relax for preferred partners making reproduction easier. But not as easy as a straight tract.
So we have convoluted tracts for the females... What do the males do? They create corkscrew penises. This goes back and forth, male adaptions force female adaptions. There is no directional selection of a fixed trait. There's coevolution based on frequency dependent selection. It's the Red Queen dynamics (that's the "it takes all the running you can do to keep in the same place" line from Alice in Wonderland). It's where male and female traits keep escalating against each other rather than converging on one fixed "best" trait. Rather you get a lot of opportunity for variability across the popultion and through generations. This is causal without being teleological.
Finally, there seems to be evidence that this can end in mutualism, but not guaranteed. I'm a little surprised you weren't more curious about this little factoid when I presented it and chose to close on your best understanding.
Anyway. I believe in unintelligent design.
It’s always random mutation that then ends up being a positive thing and those animals then reproduce more.
Nitpick: evolution is often random mutation that doesn't produce a negative impact. For example, a random mutation in humans producing certain hair colors is not negative, but doesn't necessarily give an advantage either, so we have a distribution of hair colors.
(I'm ignoring people having a thing for people with a certain hair color because I doubt it's statistically significant. If anything, it's probably more an unconscious preference for people with uncommon attributes, meaning more genetic diversity.)
Organisms that enjoy sex reproduce more.
Organisms that enjoy having sex until genetic material is exchanged reproduce even more.
In mammals where reproduction can decrease fitness of the females (being pregnant means worse hunting, or worse at evading predators, and more needed calories) the females tend to be selective. There is an evolutionary pressure for them not to attempt to reproduce with every male they see. If they did, they would likely cut their own life short and the offspring may not make it.
So their orgasms become more elusive, and often include outside factors than the physical actions as well. For them the evolutionary pressure isn't just to have sex, it's to have sex with someone who could keep them alive during pregnancy, childbirth, and until the offspring are self sufficient. Not just capable of that, but willing. That's the whole "emotional connection" thing, and why most women aren't just hung up on looks.
But to clarify this is something way older than humans. Because orgasms have been around a lot longer than we have. Humans just have the language to d scribe the behavior it doesn't always mean we understand our own.
Same as every other evolved feature. Random mutation results in better reproduction. If orgasms felt bad, people would avoid them, and very few people would reproduce. For people who they feel good, they seek that reward, and reproduce more.
If orgasms felt bad, people would avoid them, and very few people would reproduce.
Quite a few things about the reproductive process can feel bad. Ask any woman with a yeast infection or any guy with an exposed wound on his genitals (perhaps from an STD). The sexual drive is more than just the superficially sensual. And very few organisms are documented to experience the kind of chemical release associated with it, despite all of them engaging in reproductive activity.
The orgasmic release has a long-term social role, encouraging pair bonding between partners and inhibiting aggression in the male immediately afterwards. So maybe less an incentive to have sex and more an incentive not to kill your mate when you're done.
And very few organisms are documented to experience the kind of chemical release associated with it, despite all of them engaging in reproductive activity.
As in nobody's looked, nobody can tell, or there's demonstrably an absence?
nobody’s looked
Animal reproduction is exhaustively researched.
Some parts of it. If you want to know about bird mating dances, you're set. If you want to know something more specific, or about an unpopular taxon, you might not be. You said "very few animals", implying this would be true for nearly everything that's not a human.
Without more information, it seems like the kind of data that would be available for a couple lab workhorse species if anything at all, since it's brain- and subjective experience-related.
Cue the "my wife wants to kill me whenever we get done having sex amirite boys? Herpaderpaherp!" boomer hoomer hehehe
Horniness is a weird thing. You'll climb over rusty nails for sex even if you don't get the Big O with any reliability.
It doesn't really leave fossil evidence, and we're not anywhere close to genetically or taxonomically reverse-engineering the brain, which is where they happen. So no, we don't know "how" it evolved.
The fact we can masturbate also undercuts the "why" a bit, but it wouldn't be the first time a thing that evolved, and then was undercut by later developments.
https://onlinelibrary.wiley.com/...
See above for a possible explanation for the evolution of female orgasms. Tl;dr: in humans, it may be a trait derived originally from induced ovulation in more evolutionarily distant ancestors and changed to become what it is in humans over evolutionary time.
In a general evolutionary biology sense, "why" questions are a lot harder to answer than "how" questions. Many answers to "why" that are often given as "that makes sense" are often untested "just so" explanations.
we would have to figure out how and why pain evolved. Our whole endocrine system is split between feel bad and feel good chemicals to get us to do things and not do things.
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Evolution is never a causal relationship even though school books often teach it that way. It's never that a feature evolves with an intent to make a change. It's always random mutation that then ends up being a positive thing and those animals then reproduce more.
So, in this case those people who developed the mutation ended up having more sex and thus reproducing more. The ones who didn't have it either had reproduced with those who did and thus their descendants ended up with it, or they didn't reproduce enough and died off.
That's how all evolution works in reality. The trait either makes it easier to survive, makes reproduction easier (or more survivable), or it makes the mate more appealing and thus more want to mate with the people with that trait than without.
Basically everything else is either connected to one of those traits, or there were other external factors that made that group more able to survive and reproduce and thus the trait had no real reason not to exist and just was random chance.
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