However, the reason I’m skeptical about reciprocity being the determining factor, is that, if there’s no cheap cost of coercion, there’s no easy way to enforce the ‘reciprocity’ part.
There’s no incentive to help foreigners who might not stick around.

Cooperative group living can indeed be successful to the cooperators, but in almost every other non-human society, it doesn’t work with non-kin altruists.

This is because there is almost always some cheater who realizes that he can be very successful if he takes from the cooperators without giving anything back. Since a cheater is almost physically stronger, the cooperators will likely put up with the cheater rather than pay the cost of coercing the cheater.

If the frequency of cheaters is high, than cooperation is simply not worth it, especially with non-kin.

It is our ability to suppress cheating that makes altruism worth it. I wrote a new blog post on this topic, actually.

It would be interesting to compare the effect of actual physical punishment vs the loss of cooperative relationships. Perhaps neither one is sufficient and some elements of both are required? This makes me want to study game theory some more, haha.

Humans’ unique throwing ability has allowed for this.

While this doesn’t force every individual to play along - there are still aggressive individuals who take more than they give - it still does allow for non-kin social cooperation to develop, which allows for large social units to form.

This idea is the basis for the class I’m taking. And even if it’s not exactly right, I have to pretend to get full credit. :D

Hmm. I would have to disagree that coercive threat was necessarily cheap. There is often a cost for punishing cheaters - the family of the cheater might retaliate, you might gain a less than positive reputation in your group for your violence, etc. If you look up collective action problems, this is considered a second order collective action problem. Religion is hypothesized to have developed as a solution to this problem. A supernatural being takes the responsibility of carrying out the punishment, even if it’s only promised punishment in the next life. This way, no individual in the group has to pay punishment costs but they all benefit from the cheaters being discouraged.

This is just a speculation extending from a class discussion. I haven’t read any literature on the subject even.

Thinking on the primatological data, it fits your hypothesis somewhat. Bonobos practice female homosexuality (quite frequently) and also have strong female social bonding. Who knows where the causation is, though.

The data suggests that human brain development and slow infant growth was enabled by the development of large scale non-kin dependent social cooperation. The latter was only able to develop because of the cheap cost of coercive threat by cooperators against cheaters.

That being said, in this example, females would engage in kin-independent homosexuality in order to delay child birth, which would be reciprocally altruistic. However, individuals who refused to “give” wouldn’t be able to cheat and just “receive” the benefit of female homosexuality. Because there is the cost of coercion is low for the female cooperators (just throw a rock at the cheaters head).