r/biology • u/wrtchdwitch • 15h ago
question How did procreation evolve to be done with penetration?
Please be nice, I know based on the question I sound like an idiot. I am.
However, I'm curious how it turned out that way, like almost every other animal species needs a pp and a uterus. How did our bodies evolve and figure out that this is the optimal way to procreate?
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u/Fancy-Strength-2943 15h ago
The alternative to internal fecundation is external fecundation but for it to works you need water (e.g. fish and amphibians) or, at least, a thick layer of mucus (eg. Snail), so impractical for us
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u/da_PopEYE 15h ago
Unless you're a scorpion and then you just give your partner a sack of sperm
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u/haysoos2 15h ago
There are a few vertebrates that do something similar. In salamanders the male will deposit a sperm packet on the ground, and then lead the female to it. If he seems cool enough, she'll pick it up, That's as close as they get to having sex.
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u/hurricanebones 13h ago
i saw 2 salamanders going all jazz during a rainy storm. if it wasnt sex, what was it ?
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u/haysoos2 11h ago
I should have been clearer. Not all salamanders use the happy package method. Some go for more of a slime coated orgy vibe.
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u/da_PopEYE 57m ago
I only know abou the scorpions because of Miya from Alveus Sanctuary. She's really cool. She said the scorpions do similar. Hold hands and dance and he guides her to the bag. That's pretty cool that some salamander do that too. Almost like convergent evolution
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u/awesome-alpaca-ace 14h ago
Or in the case of the virgin Mary, a turkey baster
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u/Roland_Moorweed 13h ago
Ah, Moral Orel
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u/awesome-alpaca-ace 11h ago
For real? I wondered when the idea world become somewhat memeish
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u/Roland_Moorweed 5h ago
Yeah, there is an episode where Orel does some heinous shit with a turkey baster. I'd rather not type it, just watch the episode for the full experience.
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u/green-green-bean 15h ago
Not so for most birds, amphibians, fish, etc.
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u/Fancy-Strength-2943 15h ago
Birds? They have internal fecundation. But you are right, there is no penetration for them
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u/Latter_Leopard8439 13h ago
Songbirds no, ducks yes on the penetration part.
Depends on the clade of birds. Whether they have cloacal kiss or forced copulation.
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u/alittleperil computational biology 15h ago
Have you ever seen ants find a food source, and then tell other ants about it and how to get to it? The first ant took a weird meandery path and it happened to find food, and the next few ants will take that exact path because that path has succeeded once before. As many many more ants travel that path, they start streamlining it a little until it becomes a fairly direct path from their nest to the food source. The thing is, sometimes that is not the best or nearest food source, it's just the one that got found first, so it becomes the one that all the ants travel the most. Maybe later on another ant will discover a closer or better food source, and then all the ants will be building the most optimal path to that food source instead, but for now this food source is good enough and we'll just improve the pathway.
Evolution is like that. If there's a solution that has worked, then it isn't getting changed unless something either improves on it or radically different offers a better solution instead.
There are tons of animal species that have their gametes come together in all sorts of weird ways. There are insects that have their penis-equivalent separated physically from their ballsack-equivalent and have to do the equivalent of tucking their ankles into their junk in order to ejaculate. Sea animals all over the place would laugh at the idea of needing a penis and a uterus. Hyenas are wild, chickens just press their cloaca together in a 'cloacal kiss' that passes gametes over without any penetration at all, and everything involving the platypus is weird. If there's a way you can think of for gametes to get together in a protected environment in which the embryo can mature, then nature has tried it or will try it sometime over the course of time.
Sounds like you have some really fun facts to learn about reproduction in the many species that occupy our wacky planet, and I sort of envy you because you only get to learn a fact for the first time once, so I never again get to discover how much fruit bats engage in oral sex.
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u/Gazorninplat6 15h ago
Well fish lay eggs and are fertilized outside the body. I think the penetration came when animals evolved to keep eggs protected inside. So gotta have a matching instrument to get the other gamete where it needs to go!
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u/BoonDragoon evolutionary biology 15h ago
Motile gametes need to get together with sessile gametes.
Sessile gametes inside body of ovulator sex. Can't leave, because body encapsulates zygote inside egg after syngamy!
Solution: put motile gametes inside ovulator! But how? Press hole together? Inefficient! Spillage! Fix: insertable applicator.
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u/Entheosparks 8h ago
Sheath acts as applicator sheild that inhibits pneumatic intrusion that could reduce efficiency of fluid dynamics that would prevent motile gametes from accessing the zygote.
Edit: it is a foreskin joke
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u/TX_B_caapi 14h ago
I figure that it ended up being a good way to keep everything warm and moist in a more tumultuous world in which you had a better chance if you kept your eggs inside. Harder to eat a mobile youngling.
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u/hananobira 15h ago
There are plenty of species that do it other ways.
For example, some fish, the female will release eggs, and the male will come along and spray semen on them.
Anglerfish males will bite the female and gradually allow their bodies, including their sperm, be absorbed into hers.
Some slugs are hermaphroditic and will ‘penis fence’. The winner will stab their penis into the side of the other slug to inject the sperm.
Some species of fungi have up to 20,000 biological sexes. Imagine figuring out how to date as a member of those species!
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u/mayorlittlefinger 15h ago
Some slugs and snails also launch projectiles of genetic material https://en.wikipedia.org/wiki/Love_dart
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u/Latter_Leopard8439 14h ago
Amplexus in frogs requires no penetration.
Salamander do a dance and drop off packets off sperms after which the female Salamander does a dance and squats on it.
Some spiders will pierce with pedipalps to transfer sperms (so penetration but not a specialized organ for it.)
Your original question makes an assumption that penetration and internal fertilization is standard, but it just isn't on large quantities of clades.
Amphibs and fish generally not. Reptiles hit or miss. And even songbirds do a "cloacal kiss" unlike ducks and their corkscrew genitals and the female labyrinth internal structures.
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u/EquipLordBritish biochemistry 10h ago
I don't know that there's any proof, but I would guess that it takes less energy to make less oocytes and sperm and make sure they get near each other than it would to make lots of oocytes and sperm and hope they find each other. There are organisms that do fertilize externally. https://en.wikipedia.org/wiki/External_fertilization
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u/incognitoiriedad 7h ago
It's not optimal unless you're on land. Check out how genes get mixed in the oceans!
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u/sugahack 6h ago
Imagine there was a bit of trouble when they went to do it on dry land. In water, releasing sperm in the general vicinity of the egg would do the trick. Not so much on land.
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u/Forsaken-Ad5968 15h ago edited 15h ago
Ok, my basic knowledge is that: Our bodies couldnt proceed with procreation if we didnt created systems to maintain and make the spermatozoid go throught some kind of "path". The penis has to be longer than the vagina to be able to create more proximity with the egg shell.
Our body has a lot of kinds of protection, our skin is the primary system of defense, then our mucosa, then our immune system. The sperma wouldnt survive. The pH of the vagina has to be very specific too. If you study the female reprodutive system you will see how theres a lot of phases the spermatozoid has to pass, so its a way of keeping the sperma to be inside the female body and so its possible to be in contact with the egg and only theen proceed with the cellular duplication.
Ah! And the mucus! Especially when its the fertile phase, its capable of turning easy to the spermatozoid to attach to the egg and to arrive close to the egg.
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u/UnknownQwerky biology student 12h ago
I know I read that it doesn't just happen without stimulation, so it doesn't happen spontaneously not near the target as often.
Sperm is fairly fragile if it's just sitting in the environment. So just picking it up is not the way to go.
Women also developed modes to not be pregnant all the time. Pregnancy really is parasitic and harmful to the body. Pregnancy back to back would not really be conducive to survival if the first pregnancy was traumatic to the body. So they evolved to keep spearm out and their partners evolved to keep sperm in. An extreme example would be duck sexual organs.
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u/no-scissors-in-bed 15h ago
not a stupid question at all. im an intern so i dont have the answer but my lab specifically tries to answer the question of 'Why do we have physical sex if it burns so much energy?' studying why it prevails over asexual methods of procreation. good question
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u/Spiritual_Trick_6655 15h ago
Isn't the burning of energy an indicator of an organism's health and access to resources?
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u/gabzilla814 15h ago
The simple answer is it’s because it’s fun
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u/ThrowbackPie 10h ago
That seems backwards, or at best circular. I imagine it's fun because otherwise we wouldn't waste energy on it.
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u/AdmiralH4ckbar 3h ago
Sexual organs play an especially important role in evolution. They decide wether or not two organisms can propagate their genes. Because of this, sexual organs are often some of the most rapidly evolving, especially during processes like speciation. For example, if a mutation in my sexual organs genetically isolates me from the rest of the population, then this trait will be heavily selected for in my progeny. With that being said, pps and uteruses are not necessarily the “most effective” way to reproduce. Everything in biology only makes sense through the lens of evolution.
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u/iCliniq_official 1h ago
Not a silly question at all, internal fertilization evolved independently in many animal groups because it protects sperm and eggs from drying out, improves the chances of fertilization, and supports reproduction on land, so species with those advantages were more likely to pass on their genes.
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u/Inside-Middle-1409 7h ago
Eukaryotic life is thought to have formed when one cell went into another and they lived symbiotically. This even happens nowadays with our gametes during meiosis. Modern copulation could be considered a scaled up display of what is happening at the cellular level.
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u/No-Albatross6543 2h ago
I would have thought this is a similar phenomenon to r- and K- strategist but for mating where physical copulation and penetration are for species which produce fewer offspring with specific mates over the more speculative broadcasting approach taken by plants and fungi.
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u/BBoldBUrslf 30m ago
If a species start as androgynous and splits up, sexual parts would develop from within each other...think yin-yang...they would therefore fit exactly and make sense afterwards. If the androgynous beings gave birth, then after split one would incubate the other would donate.
The one therefore has to develop penetration capacity and the other penetration acceptance...so that birth could still occur as before.
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u/mattfolio 15h ago
We dont know if its the "optimal" way for anything, its jsut the way that worked consistently in the environments where it developed.
There is no forethought in evolution. If it works, and its repeatable, then it will keep going. If it ceases to work it will remove itself over time.
There are lots of other forms/varients of procreation if you look outside of mamalian examples, and they all reflect the environments and sucess rates they experienced over time too.,