That is a good question. The logic I have heard about it, is that male mammals in general are in competition to have sex, because the more sex they have, the more likely they are to reproduce. With all males acting like that, though, you can have some serious competition selected. That competitive drive has been tempered in humans to some degree, because human young require a lot of care, and a man is also more likely to reproduce if he helps to take care of a pregnant woman and offspring. At some point in the distant past, one theory is that mutations that lost estrus gave an advantage in trading sex on a regular basis for help, which worked. Things like falling in love with a specific other, also helped. We are also highly social animals and it works better for men to cooperate with each other within groups. But tensions remain. A man isn’t necessarily doing well to take care of someone else’s offspring, but the man who fathered the child is getting more of his genes into the next generation with less work on his part. Men will also cooperate with their group- but other groups, not so much, especially if they speak a completely different language, different culture, but such concerns seldom extend to whether their women are suitable to have sex with. Sometimes, though, hunter gatherers are reported to have tried to exterminate another group, so that isn’t always true. But specific mitochondrial genes passed by women, have seldom been lost, while y chromosome genes passed by men, are often lost. It has still often worked for men to be physically aggressive about fighting all out for sex, in spite of it generally being bound by rules of non lethal competition within groups. Aggression and sex are still linked in male brains. Threats to life bring out aggression and that is linked to sex.

But while that has worked enough in the past for instinctive reactions to be passed down, winning at conflicts can also selects better ability to think logically and while a potential dieoff can bring up similar instinctive reactions to the competition to survive such problems, the instincts are a lot less likely to work with regards to sex, as well as other things. Spreading your seed as widely as possible can work when there are plenty of resources around and women are likely to live and raise the children, but when resources are scarce, and the additional stress of pregnancy, birth, and nursing are more likely to kill both woman and child, then as you have seen, it is a counterproductive strategy.

We have been increasing the amount of resources we could take to grow population with new innovations in tools and domestication since the Neolithic, so quite often the aggressive strategy has worked. I think this is coming to an end.

In 1979, I read “Limits to Growth”. I was on track to graduate with a degree in mech. engineering, but the book, and similar books, disturbed me. People told me that we could safely ignore the projections of “Limits to Growth”, because we had found ways past limits in the past, so we would do it again. On the surface that sounded logical, but when I looked a little closer, I realized that this was not a logical conclusion at all. People were depending on finding things that were imaginary. Looking for imaginary things doesn’t mean you will find them. I can imagine all kinds of things, like unicorns and flying dragons, but would I bet my life that they exist? No, I wouldn’t. Looking doesn’t cause finding with imaginary things. I couldn’t say it was impossible that what people want will be found, but I could say that the expectation wasn’t rational. People were confusing correlation with causation with the statement that because we had found ways around limits in the past, we would do it again. We weren’t being scientific, and I felt we were very likely to come to serious grief on the matter. If we behaved logically, we would find what we needed and test it very well before we bet so much on it. But most people have dismissed this concern completely.

I also considered how we were measuring value, trying to understand what we needed to do to incorporate the above understanding into economics, assuming people might be found to want to behave with rational expectations about the future. Eventually I realized that people are highly social animals, we live by teamwork and die without it. This observation can be tested by anyone, we all have the naked body to test our independence of social groups. Teams can be more or less energy efficient at getting everyone enough food, shelter, and reproduction, and they can have more or less rational expectations about the future, as well. Expecting to find whatever you need when you need it, isn’t rational, but seeing the future exactly, also isn’t at all likely, either, which is why I think we have degrees of rationality about it. Hopefully we see it clearly enough to survive and adjust where we were off the mark in what we thought would happen.

Something I should have mentioned above, is that while male mammals have generally been selected to be aggressive about sex, and females to be nurturing to offspring, the fact that aggression doesn’t work, nor do instincts for nurturing work, when serious scarcity is an issue, shows up with animals selected for seasonal breeding. Animals in temperate climates have generally been selected to have offspring in the spring. Animals have also been selected to avoid having offspring during regular, or irregular, periods of drought. No amount of aggression or nurturing makes up for problems of scarcity of resources. If people can see the logic of this and understand that we are facing problems of severe scarcity, then putting energy into surviving the scarcity rather than into reproduction, makes more sense.

The problem is whether to follow logic, or follow instinctive urges. The latter I know, can be very strong… I would say this is a situation where being able to override instinctive urges and be logical, is more likely to succeed.

There is a lot more that can be said about all this, but these are the basic things I’ve seen about it. I respect your ability to put aside your emotional reactions and write about these things, and try to do the same.

One thing I have doubts about with your post is the idea that female reindeer can absorb the fetus when stressed… Perhaps under when the fetus is very young? I’ve never heard of this. There is an example of reindeer introduced to St. Matthew’s Island at the end of WWII. They were meant to be an emergency food supply for the men operating a radar station there, but they were left behind when the war ended. They reproduced from around twenty or thirty, to an estimated six thousand, then nearly all died with a bad winter. No fertile males survived, though a few females did. Likely the male aggression to breed left the males in poorer condition- male deer are known to often have high winter kill even in ordinary winters because of this. Fits with everything we are considering here. Skeletons were found of fetuses inside the bones of their mothers… https://www.geo.arizona.edu/Antevs/nats104/00lect21reindeer.html

Something else I find interesting about our evolution is in Richard Wrangham’s ideas about how male coalitions have domesticated us, making men much less likely to do acts of reactive aggression compared to chimpanzees, but proactive aggression remains. He thinks female coalitions domesticated bonobos, though with a different approach. Wrangham thinks male coalitions killed bullies taking whatever they wanted when they wanted it. He thinks female coalitions of bonobos, have controlled which males reproduce and that has also resulted in domestication of them. Male bonobos don’t reproduce unless they have high status with the females, and having high status requires a relationship with a female- usually his mother. If she dies, his status drops and he is unlikely to reproduce. Perhaps you know about this? He goes over it in this video. It sounds plausible to me, certainly fits the observations that have been made. https://www.youtube.com/watch?v=c2TOxoE5QCg

Malcolm Potts has written a wonderful book on this topic, Sex & War, if you’re interested! https://www.amazon.com/Sex-War-Biology-Explains-Terrorism-ebook/dp/B003UBAX3A

Rape is a breakdown of normal behavior. It is more violent aggression than desire for sex. Rapists are angry violent men who use rape as a means to express their violence. If rape becomes more prevalent in times of famine it is because men are angry and social norms and laws are breaking down. I doubt rape becomes more prevalent without other types of aggressive acting out also becoming more common.