Christopher Boehm is an anthropologist and primatologist who is currently the Director of the Jane Goodall Research Center at the University of Southern California. He believes that suppressing our primate ancestors’ dominance hierarchies by enforcing egalitarian norms was a central adaptation of human evolution. Enhanced cooperation lowered the risks of Paleolithic life for small, isolated bands of humans and was likely crucial to our survival and evolutionary success.

In theory, labor is divided by gender in current hunter-gatherer tribes as well, but unless they hunt big game regularly, they don't seem to be paid much attention to. These cultures, although vehemently egalitarian by design, are also very geared towards individuality, and unless it's breaking religious taboos or hurting someone else, people pretty much do what they want. Also, in many forager tribes, gatherers still provide the bulk of the daily food.

One example is the !Kung, "While men tend to hunt and women tend to gather, these roles often overlap. Women retain control over the food they gather. Both men and women raise children equally."

The following is one of the best, most clear and succinct explanations I've ever seen. It comes from The World Economic Forum and explains how and why that changed with the rise of agriculture:

“Labor roles became more gendered as well. Generally, men did the majority of the fieldwork while women were relegated to child-rearing and household work. Without contributing food (and by association, without control over it), women became second-class citizens. Women also had babies more frequently, on averageonce every two years rather than once every four in hunter-gatherer societies.

Because somebody had to have control over surplus food, it became necessary to divide society into roles that supported this hierarchy. The roles of an administrator, a servant, a priest, and a soldier were invented. The soldier was especially importantbecause agriculture was so unsustainable compared to hunting and gathering. The fickleness of agriculture ironically encouraged more migration into neighboring lands in search of more resources and warfare with neighboring groups. Capturing slaves was also important since farming was hard work, and more people were working in these new roles.

This division of labor and social inequality had very real consequences. For instance, while the majority of people had disastrous health compared to their hunter-gatherer ancestors, the skeletons of Mycenean royalty had better teeth and were three inches taller than their subjects. Chilean mummies from A.D. 1000 had a fourfold lower rate of bone lesions caused by disease than commoners.”

Humans are naturally cooperative. We're one of the most social species on the planet. That doesn't mean that it doesn't benefit from social reinforcement from time to time, but studies have been done on babies showing them being willing to share their food, even when they are hungry, and even with people they don't really know (in other words, not just with parents or family). Our culture is at war with our core selves. Our brain is hardwired for cooperation.

It takes two: Brains come wired for cooperation, neuroscientists discover

https://www.sciencedaily.com/releases/2011/11/111103190351.htm