I was told all humans start as female and then the ovaries descend and become testis. Why are females limited in this capacity?
In: Biology
The short answer is evolution.
One male can impregnate 100 women.
100 males impregnating 1 woman still results in 1 pregnancy.
Not all species are limited in this way, species like fish which produce many thousands or even millions of eggs can produce them all through their life. They would never be able to store a lifetime of eggs, just like males of many species would never be able to store a lifetime of sperm. When you can’t store it you have to make it. But a woman only goes through a few hundred egg cells in her life and that’s easy to store a lifetime supply of.
So why would you want to store them? Well, cell division is a risky thing. There’s always a chance that something will go wrong. If your egg-generating cells are constantly producing new eggs, there’s a chance as time goes by that the egg quality will get worse and worse. But if you make them all right off at the start, that’s less of a problem (still can be a problem, but less of one).
Eggs and sperm are very different sorts of cells. Eggs are among the largest cells in the whole human species. Sperm, on the other hand, are small, disposable, short-lived cells. They are like one-time-use battery gizmos. Pull out the insulating tab and light blinks until the battery dies.
We actually see in other mice that females can produce eggs after they are born and I believe they also found that if they graft the human ovarian stem cell onto mice they also produce eggs. I don’t think they have seen it in humans though because they can’t experiment on a living person. But perhaps we could transplant these cells in women who are struggling to conceive.
https://www.sciencedaily.com/releases/2012/07/120726180259.htm
Limited or freed?
The answer is no one knows why. There are tons of theories, most of them centered around medical misogyny and the idea of a woman’s “usefulness”.
The fact is, evolution doesn’t work that way. If it doesn’t kill the whole species, it gets passed down.
The answer has to do with sexual competition in all sexual species. Females spend more energy on fewer and larger gametes while males compete making many small gametes which only have a small chance if making it to fertilization. A female doesnt need a shit ton of eggs. She only needs one for every menstrual cycle. It’s not that females are limited, really males are wasteful. Males compete with each other by producing the most sperm. If a man has sex with two women in the same night they can both have his children but if a woman has sex with two men she can only bear one child at once so the one who gave her the most and strongest sperm has a better chance. If our primate ancestors hadn’t been so polyamorous maybe males wouldn’t have to spend their energy making thousands of sperm but that’s how things are.
Consider what could be called reproductive strategies that evolved over time.
clams: millions of sex cells squirted into the water, left to themselves, odds are some small percentage of that million survive.
elephants: 1 baby every year or so but it’s closely watched and most of them born (absent human fuckery) will survive.
Both are successful in their way. Humans evolved into two different sexes (for other reasons) and they evolved in different directions.
Here is a shower thought for you: A pregnant woman is also carrying any future grandchildren inside of her.
Humans do not start as female! We start out as **indifferent**. Around week 7 of gestation, if we have a Y chromosome we go towards the male pathway and if we dont have a Y chromosome we go towards the female pathway.
Ovaries dont become testes, a group of stem cells either become ovaries or testes depending on the signals they receive.
Also the female body is only physically capable of bearing children successfully to term for so long, so why keep producing eggs after that?
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