Humans have a lot of pro-social tendencies.

There's actually a lot of evidence in primates and other animals that they return favors.

Empathy probably started out as a mechanism to improve maternal care. Mammalian mothers who were attentive to their young's needs were more likely to rear successful offspring.

I'm personally a nonbeliever, so I'm struggling with if we really need religion.

The development of family entities enables men to cooperate far more effectively. Instead of constantly competing for the women with other men, each man essentially has a partner assigned to him, one with whom he can establish a family.

Exclusive homosexuality is not very common in nature.

Armies are a purely human invention. Most soldiers who go to war nowadays don't even do it because they're inherently aggressive.