the other was the fact that the genes for our limbic system (the emotional machinery of the brain) are inherited from our fathers

Exchanges have meaning only when there is an existing relationship to give them meaning.

Speaking in turns without interrupting each other, adding meaningfully to what the other person has just said, judging when it’s appropriate to start a new

If your community is a large one, you get the standard pattern; but if it is small, you have fewer opportunities for weak relationships and so invest your unused time in creating more close friendships.

men tend to resort to physical forms of punishment, whereas women tend to rely more on psychological punishment – a strategy deployed to particular heights by adolescent girls.

males called more different individuals than women did up to the age of thirty-five, after which the ratio reversed.

Neuroticism dimension in female groups.

A Duchenne smile is encouraging of further interaction, whereas a non-Duchenne smile is indicative of uncertainty and nervousness.

forty-five hours spent in each other’s company after first meeting for someone to progress from being an acquaintance to becoming a casual friend.