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Evolutionary Origin of Penile Reproduction

Discussion of everything related to the Theory of Evolution.

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Evolutionary Origin of Penile Reproduction

Postby prodhive » Tue Feb 16, 2016 4:50 pm

At some point in the evolutionary development of mankind, the penis (at least as a reproductive organ, not just an excremental one) must have spontaneously mutated into existence. I am also assuming that the mutation for the corresponding vaginal reproductive system must have occurred within the same creature, because the odds of two creatures of the same type in close proximity spontaneously generating compatible penile-vaginal reproductive systems, finding each other, and reproducing, seem impossibly low.

Actually, for the sake of my question, it doesn't really matter if it happened that way (excluding the possibility that large numbers of creatures spontaneously developed these apparatuses simultaneously, which again seems virtually impossible).

My question is this: wouldn't the development of a penile reproductive system have made this creature immediately sexually incompatible with any other creature of similar type, or really of any other creature in existence? How did it reproduce to sustain the mutation? The only possible explanation I can come up with is that somehow there was a reproductive mutation within a parent creature that itself had the previous reproductive system (either through sexual or asexual reproduction, though, correct me if I'm wrong, no creature complex enough to sustain a penis could reproduce asexually), and it must have generated both a male offspring with a penis and a female offspring with a vagina, and those must have interbred. Is there a better explanation?

Expanding on that, assuming this is accurate, wouldn't that mean that the evolutionary line of that creature would basically be limited to that specific creature and its offspring? In other words, it couldn't spread its mutation to any other of its kin, as they wouldn't have the proper equipment to mate. A whole new species would have to be formed solely out of that one creature that contained the reproductive mutation, and would develop entirely out of its intrabreeding descendants. Furthermore, wouldn’t this be the way it would have to happen every single time a new reproductive system was created, owing to immediate sexual incompatibility with similar creatures? Wouldn’t all mankind, for example, from the second the first proto-man became sexually incompatible with the monkeys he evolved out of, have originated from a single proto-man and his incestuous children?

Please help! Thanks in advance.
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Re: Evolutionary Origin of Penile Reproduction

Postby raymarchant » Mon Apr 25, 2016 12:41 am

You are not thinking of evolution in the correct way. It is usually a slow process with any population having a degree of variation within it in perpetual flux.

Penises and vaginas have been around since before mammals. Every population of mammal already had them.

Equally, there wasn't a first man and first woman. And even if you did decide to call this one eve and this one adam, they didn't evolve without sexual organs and then have to spontaneously evolve them.

But I'll try to look at this from your perspective of an ancestor of modern human. We'll call it population A.

Population A looks similar to modern humans but have slightly smaller brains and live in small collections of families co-operating in providing for the next generation.
Within their groups there is a variety of penis sizes and vaginal sizes. Just as today in modern humans.
Humans have comparatively large penises with respect to other apes. Probably more importantly from an evolutionary point of view, women are capable of giving birth to babies with larger heads - a necessity of the larger brains. At the same time, babies are born helpless to keep their birth size to a minimum. For the children to have a reasonable chance of reaching maturity, it is better for the mating couples to form a bonded relationship, and to a lesser degree, for the wider group to support each other. So a good match between penis size and vaginal size is a good thing - and for the sake of the next generation, there would be limits to the acceptable amount of variation within population A.

So here's the state of flux within this population:
There is an evolutionary advantage for even bigger brains. But there is an inherent risk of death during childbirth.
The population might remain unchanged for hundreds of generations, or they might gradually push the brain size up very very slowly.
If something changes in the environment that makes larger brains even more advantageous, the rate of change within the population could increase quite rapidly. Or if the opposite becomes true, the size of brains in the population might decrease quite rapidly. Evolution doesn't have a plan or goal, and is not traveling in any particular direction.
Population A would continue to exhibit a range of sizes of brain vagina and penis. But the average would change (if there was an advantage).
Sexual selection would also play a large role, but given the need to be able to support one another to rear the next generation, the emphasis would be on trust and the ability to provide.

If you could take an individual from our original population A and time travel them a thousand years into the future, they might notice that they were in some ways different from the new population, but they'd almost certainly be capable of breeding successfully with them. If however you could time travel them a hundred thousand years into the future. The ability breed with the others may have been lost. For any number of reasons.
But there is no point along those years at which you could point to a breeding couple and say "They were the first modern humans".
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Re: Evolutionary Origin of Penile Reproduction

Postby missplat » Wed Sep 14, 2016 1:00 pm

However it happened (not, obviously, with the help of magic spirits) each species starts as a cell with its own, complete set of chromosomes, n, unique to it and found in the egg (ovum). Bacteria still represent this kind of species and reproduce by mitosis (simple splitting). Each subsequent individual is identical to its progenitor and is able to carry out its functions of energy gathering, energy use and expelling of waste on its own. Each flies, swims, floats with its multitude of sisters in the biosphere and will do forever.
However, some species became multi-celled and used somatic cells to make organs (a body or plant). Somatic cells must have 2, identical, matching sets, 2n, possibly achieved by an incomplete splitting; the 'returning' cell was itself incomplete and so added a second nucleus. Now the cells, with 2 sets, were able to become somatic cells and make a 2n part of the life cycle. As soon as the new zygote was made, millions of new n individuals were made, to await their chance of the 2n part of the life cycle in the ovary.
The 'sexual' organs are merely cells making organs to provide the second set; the ovaries are adapted to make and store sperm and the vaginal channel is extruded to provide a way to add the second set.
This arrangement is achieved by cells in every species that has a body or a plant. It has not 'evolved' in humans; how cells 'know' what to do is the problem that has not been solved convincingly, in my opinion, by theorists, but I think cells in all species carry out the same functions (making skin, livers etc) and these are related to the bacterial actions.
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