That just isn't true we have Neaderthal bodies with signs of violence on them, some societies were less hostile than others but that more depends on geography and resources. In Africa there was families who were clearly bound and beaten to death over 20,000 years ago. The idea of the peaceful hunter-gatherers just isn't true, there was definitely places and cultures that were more peaceful but a lot of that was again just dependent on resources. Person to person today, regardless of what economic system you live in, people are actually less violent than they used to be.

I also would say we did not stop being altruistic, we built a system that makes it difficult to be. But people are exceptionally kind today in a lot of places.

I think you decided how you feel on this topic so there's no point in going on. But you should look into it, you're falling into a classic trap that doesn't allow you to view the world complexly and you're convinced all violence stems from capitalism or something. Overall, violence was a daily way of life for many people and cultures don't suddenly just flop to violence, they develop it slowly over time. We have also over time developed better ways to interact and our population size shows that. While poverty is a problem and widespread, the base level of existing is far more comfortable than it used to be just look at the infant mortality rates and the average life span.