Family is easy; your kin group which is defined and preferred through inclusive fitness. Friends corresponds to that circle of individuals with whom one practices reciprocal altruism (qv). Since reciprocal altruism requires trust extended over time, it's not surprising that friendship tends to be psychologically regulated.
"According to Trivers, the following emotional dispositions and their evolution can be understood in terms of regulation of altruism.
- Friendship and emotions of liking and disliking.
- Moralistic aggression. A protection mechanism from cheaters acts to regulate the advantage of cheaters in selection against altruists. The moralistic altruist may want to educate or even punish a cheater.
- Gratitude and sympathy. A fine regulation of altruism can be associated with gratitude and sympathy in terms of cost/benefit and the level in which the beneficiary will reciprocate.
- Guilt and reparative altruism. Prevents the cheater from cheating again. The cheater shows regret to avoid paying too dearly for past acts.
- Subtle cheating. A stable evolutionary equilibrium could include a low percentage of mimics in controversial support of adaptive sociopathy.
- Trust and suspicion. These are regulators for cheating and subtle cheating.
- Partnerships. Altruism to create friendships."
2. Birds vs Frogs (or Lee Smolin's seers vs. master craftsmen)
Freeman Dyson calls mathematicians who take a lofty conceptual view of their subject birds and those who work in details and solve their problems consecutively frogs. Smolin has a similar division in mind for theoretical physicists.
The crisp distinction is between deduction and abduction. Deduction draws consequences from theories and boundary conditions - and is the home territory of the master craftsmen and frogs; abduction is the creative synthesis of the most parsimonious and elegant theory which can be conjured up to explain the available data - the business of seers and birds.
(Your author, to tell the truth, has always felt more avian).