Morality, after all, has nothing to do with selflessness. On the contrary, self-interest is precisely the basis of the categorical imperative.

In humans, the family prevents infanticide. Next to language, the core family, consisting of a mother, a father and children, is the greatest difference between us and other primates.

I have often noticed how primate groups in their entirety enter a similar mood. All of a sudden, all of them are playful, hopping around. Or all of them are grumpy. Or all of them are sleepy and settle down. In such cases, the mood contagion serves the function of synchronizing activities.

When we are bad, we are worse than any primate that I know. And when we are good, we are actually better and more altruistic than any primate that I know.

The primate laugh is given in playful contexts, and as such has a strong similarity to the human laugh.

As in a Russian doll, however, the outer layers always contain an inner core. Instead of evolution having replaced simpler forms of empathy with more advanced ones, the latter are merely elaborations on the former and remain dependent on them. This also means that empathy comes naturally to us. It is not something we only learn later in life, or that is culturally constructed.

If both parties have a stake in the other, the chances of them killing each other are going to be reduced.