part of william hamilton‘s theory of inclusive fitness/kin selection, which explains how altruism ever could’ve arisen at all (altruism here having a very specific definition), is that it should be possible for genes for altruism to be selected for if close kin interact regularly. kin don’t need to recognize one another for altruism to be selected for. as long as closely related individuals don’t move far from one another — that is, if a population is viscous — selection for altruism might happen.

i can’t see why this couldn’t also apply to lesser forms of altruism, not just the kind where you sacrifice your life for two brothers or eight cousins. you know what i mean. like: reciprocal altruism or nepotistic altruism. or just pro-social behaviors. whatever you want to call them. seems to me that nepotistic behaviors ought to be selected for more easily in viscous populations (if they increase fitness, of course).

and some populations are more viscous than others:

1) inbreeding populations where close relatives marry frequently over the long-term. mating with relatives must be highly viscous [insert sweaty/sticky incest joke here]. not only do the individual members of the population likely interact fairly regularly (can depend on your mating pattern), they pass many of the genes they share in common on to the next generations — who then also interact and mate. that’s what i call viscous! and, as you all know by now, some human populations inbreed more than others, and some have been doing so for longer than others. and vice versa. (see: entire blog.)

2) populations where extended families are the norm. societies where two or three generations of families all stay together, work together, play together. viscous. plenty of opportunity for nepotistic behaviors to be selected for. on the other hand, societies of nuclear families where more distant relatives are seen only once a year on thanksgiving, and then only to argue, and where your your heir is your pet cat…not very viscous. (see: family types and the selection for nepotistic altruism.)

3) socio-economic systems which push for close relatives to remain together rather than dispersing. if that sounds vague, that’s ’cause it is. sorry. i haven’t thought through it all yet. i do have an example of the opposite for you — a socio-economic system which pushed for close relatives to disperse — and that is the post-manorialism one of northwest europe. already by the 1500s, it was typical for individuals in northwest europe to leave home at a young age (as teenagers) and live and work elsewhere — often quite long distances away (several towns over) — before marrying. then it was not unusual for them to marry someone from their new locale. not viscous. conversely, many societies outside of the hajnal line (northwest europe) have had systems which encouraged the opposite.

food for thought.

(note: comments do not require an email. one of my favorite viscous food for thought!)