How can human evolution adapt to the changes of multiple births being commonplace?

Question

Mariam Nabatanzi Babirye is a woman in Uganda who has had 44 children in her life due to her bearing many children at one time. This unusual situation is because of a rare genetic abnormality that causes hyperovulation. In this fictional world, this is the norm rather than the exception. Women are likely to have multiple births of twins, triplets, etc, with single births being rare.

This situation comes with many consequences. Overpopulation would be a major issue in most parts of the world. In addition, every pregnancy is a risk to both mother and child before the modern world. In addition, there is another issue. Children who are multiples are usually born smaller than average in order to take up space in the womb. If multiple births become standard in the human race, evolution would find a way to adapt the body to accommodate this change. This would likely see a reduction in the pelvis, leading to a smaller birth canal. Our brains need to be large at birth in order to grow into the large adult brain. By shrinking the size of children, and therefore the size of the brain, it may have unforeseen consequences for us later.

How can this become sustainable without dying out after a few generations? How would the species adapt to this change?

Answer 1

A fully grown human brain won't fit through the birth canal. Instead, our brains finish growing in the six months after birth, making us an altricial species. If multiple births do have smaller brains (and I don't know if that's true), then this process should be exaggerated slightly with no net effect on adults. Tweaking or repurposing an existing mechanism to solve a new problem is the sort of thing that evolution is great at.

Keep in mind that if evolution didn't solve this problem, then multiples would be less likely to survive/procreate and singles would have already become the norm, so there must have been some solution for this situation to have developed in your world. Therefore, your question is not "can this happen?" but rather "how did this happen?"

Answer 2

The simplest answer to this really is: same as we've always done. That's just how evolution works.

This unusual situation is because of a rare genetic abnormality that causes hyperovulation. In this fictional world, this is the norm rather than the exception.

A trait never spontaneously becomes widespread. One person bears a "rare genetic abnormality" that then becomes a recognised allele for a gene (or a combination of alleles for some given genes), which may or may not become dominant if it offers an enhanced physical trait, and the population is under selective pressure by its environment. So, if the trait ends up widepread, it's because it offers an advantage over the alternative. The risk/reward ratio has to be beneficial, or it would have never stuck in the population.

So your question should probably be formulated as "What would make the risk/reward ratio beneficial for this trait?"

Overpopulation would be a major issue in most parts of the world.

One birth in each mother's lifetime would suffice to create a generation at least as populous as its parental one. Even in today's world, there are many couples that opt to not have any children, or adopt. Perhaps earlier there would have been more ressource wars (and bloodier wars, seeing as many deaths would impact the populations less than ours did), but it would most likely even out.

In addition, every pregnancy is a risk to both mother and child before the modern world.

Evolution dictates that only women who can survive these extreme childbirth conditions will live on to generate more offspring, so the risk will stabilise at a level close to the one we know. In addition, modern medicine has greatly improves the safety of childbirth. Perhaps gynecology was the first specialist medical discipline to emerge.

Children who are multiples are usually born smaller than average in order to take up space in the womb.

Yes, but we are all born quite small. We all grow throughout childhood and puberty. Perhaps we would require some more care as infants and more nutrition growing up, but I doubt this would have any real effects on adults (if given an appropriate diet).

Our brains need to be large at birth in order to grow into the large adult brain. By shrinking the size of children, and therefore the size of the brain, it may have unforeseen consequences for us later.

Same as before, our brains grow after birth, so perhaps we would be useless babies for a little longer, but I don't expect it to have a massive impact.

All in all, I don't think there are very many risks associated with that trait, if managed properly. The rewards however could be quite interesting for an early, or even medieval, human society.

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A quick sidenote on the societal aspect of this: Mariam the SuperMother is from Uganda, a country that is very Catholic in its beliefs, and like many of these countries of subsaharan Africa, sex education, contraceptives and sexual autonomy are often difficult to come by. I doubt that Mariam would have mothered 44 children if she had been born in Sweden for example. If the hyperovulation trait becomes widespread in your society, perhaps the religions would venerate a woman's bounteous loins more, and elevate them in society.

Answer 3

Women would get wider hips, so there's less strain from giving birth. Both genders producing a larger supply of gametes would cause a higher birth rate, and milk production would go up to make sure that less babies starve. And medical tech would help a lot.

Answer 4

Your best bet. most offspring die.

The only advantage having lots of offspring have in humans is if offspring only have a small chance of survival, so having a lot more offspring more is the only way to ensure you have surviving offspring. And you will just have to put up with children who grow slower.

your other option is much more abundant resources but still have a very high infant mortality so you can have normal sized offspring. but you will have basically immobile females during pregnancy, which means no nomads and likely favor multiple husbands.

Answer 5

Here's a possibility: Your hypothetical situation takes place in a world where humans are marsupials.
Marsupial joeys are born much smaller than baby placental mammals- a red kangaroo joey is roughly as developed as a human embryo at seven weeks after conception when it leaves the womb. Most of the baby's development takes place in the pouch.

With this setup, you wouldn't have to deal with the issue of fitting a large cranium through a biped's hips.

Edit: I was working off the assumption that this situation involved changes to human evolution in the (alternate) past, not in a hypothetical future.