I believe that you are wrong. In a small (hunter-gather society), where resources are scarce, people will share because they expect the others to reciprocate. If one person is holding back, hoarding food or lack of effort, everyone will know and reciprocate in kind. In a larger group cheaters can and will survive.
Capitalism is the natural result of Darwinian evolution. I think that it can be shown that labor unions and a limited central government are also the natural outcome of evolution
The concepts of individualism, self-reliance and capitalism are relatively recent. They clearly go against deep human nature.
Individualism and self-reliance are inherent in human nature. (Ask any teenager.) We trade off what we have to in order to survive (or increase our comfort level). Cooperation is what we do because we are better off if we cooperate than if we go it alone.
Capitalism is as red in tooth and claw as any struggle for survival in nature.
You kind of make my point. One of the tenets of sociobiology is that you must consider the environment in which humans evolved - the small hunter/gatherer band.
People living in groups larger than 200 or so, capitalism and labor unions are only a few thousand years old at most. MUCH too recent for evolution to have enabled us to adapt to them. It takes thousands of generations before a beneficial trait becomes common in a species.