family types and the selection for nepotistic altruism

it finally clicked in my head while thinking about polygamy what the importance of family types — nuclear vs. extended, etc. — might be in the selection for altruistic behavioral traits, especially nepotistic altruism or clannishness. i should’ve thought through polygamy sooner instead of putting it off, but hey — procrastination is heritable, too, so in the words of h. solo, it’s not my fault! (~_^)

the logic of the mating patterns/inbreeding-outbreeding theory goes that, given the right set of circumstances (i.e. certain sorts of social environments), selection for nepotistic altruism/clannishness ought to go quicker or be amplified by inbreeding (close cousin marriage or uncle-niece marriage) simply because there will be more copies of any nepotistic altruism genes (alleles) that happen to arise floating around in kin groups. in other words, inbreeding should facilitate the selection for clannishness…if clannish behaviors are being selected for in a population.

the thing is, though: the individuals carrying certain versions (alleles) of nepotistic altruism genes need to direct their nepotistic behaviors towards other individuals carrying those same alleles, otherwise their actions will be for naught. (yeah. kin selection.) if they direct their nepotistic actions towards people who don’t share the same alleles, then the actions will be “wasted” and the behavioral traits won’t be selected for — or at least not very strongly — and they might fizzle out altogether.

let’s take an imaginary society as an example: say everyone in our pretend population always marries their first cousins. their father’s brother’s daughters (fbd) even, so that we get a lot of double-first cousin marriage. h*ck! let’s throw in some uncle-niece marriages on top of it all. the inbreeding coefficients in such a society would be very high, and if clannishness was being selected for in our highly inbred population, the selection ought to move pretty quickly.

but suppose we separated all the kids at birth from their biological families and set them out for adoption by unrelated individuals — people with whom they likely did not share the same nepotistic altruism alleles. think: the janissary system, only on a population-wide scale. if we did that, there should be virtually no selection for clannishness despite all the inbreeding since pretty much no one’s nepotistic behaviors would be directed towards other individuals with the same nepotistic altruism genes. in this case, kin selection would just not be happening.

such a society does not exist, and i don’t think ever has. but there are societies out there with certain family types — namely nuclear families (or even post-nuclear family societies!) — which ought to have a similar dampening effect on any selection for clannishness.

northwestern “core” europe has had very low cousin marriage rates since around the 800s-1000s, but it has also, thanks to manorialism, had nuclear families of one form or another (absolute or stem) since the early medieval period — nuclear families are recorded in some of the earliest manor property records in the first part of the ninth century from northeastern france [see mitterauer, pg. 59]. on the other hand, eastern europeans, like the russians and greeks, while they also seem to have avoided very close cousin marriage for several hundreds of years (which is not as long as northwestern europeans, but is quite a while), have tended to live in extended family groupings. you would think that nepotistic altruism could be selected for, or maintained more readily, in populations where extended family members lived together and interacted with one another on a more regular basis than in societies of nuclear family members where individuals interact more with non-kin. societies comprised of nuclear families are more like my hypothetical janissary society above where the altruism genes that might’ve been selected for via kin selection instead fade away in the wash.

we have to be careful, though, in identifying nuclear family societies. the irish of today, for instance, are typically said to be a nuclear family society, but the extended family does still interact A LOT (i can tell you that from first-hand experience). same holds true for the greeks and, i suspect, the southern italians. i would say that these populations have residential nuclear families, but not fully atomized nuclear families which have infrequent contact with extended family (think: the english). the early anglo-saxons in england were also characterized by residential nuclear families — the extended family (the kindred) was still very important in that society. the individuals in a residential nuclear family society probably do interact with non-family more than individuals in a society structured around extended families or clans, but less so than a true nuclear family society.

the thought for the day then?: family types can also affect the selection for clannishness/nepotistic altruism.

that is all! (^_^)

previously: polygamy, family types, and the selection for clannishness and “l’explication de l’idéologie”

_{(note: comments do not require an email. irish nuclear family.)}

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mating patterns in medieval norway

at the beginning of this year i said that, since there are so many scandinavian readers of the blog (skål!), i would post about the historic mating patterns of scandinavians/nordic folks … aaaaaaand now it’s december and it never happened. (*^_^*) (did i mention that i come from a population that doesn’t have terrific future time orientation? as han solo said: “it’s not my fault!” (~_^) ) sorry!

i did have good intentions! i swear! back in april i picked up this article: “Norwegians and Europe: The Theme of Marriage and Consanguinity in Early Norwegian Law” from Scandinavia and Europe 800-1350: Contact, Conflict, and Coexistence. so now, in order to assuage my guilt, and so that i might sleep well at night once again, i am finally going to take a look at that article! (^_^)

there were four legal areas in medieval norway (indicated on map below) — the borgartingslag (B), the eidsivatingslag (E), the frostatingslag (F), and the gulatingslag (G):

each of these regions had its own set of secular laws up until the 1270s when magnus the law-mender issued a common law for all of norway. they also each had their own set of ecclesiastical laws which, of course, included regulations on marriage. although there are a couple of differences between these law codes wrt marriage, the upshot is that marriage between sixth cousins or closer was banned in all four regions as well as marriage between affinal family members (i.e. in-laws) related to one another within five degrees (e.g. fourth cousins-in-law or closer). the regulations on blood relations are in line with canon law issued from rome at the time (the ones on in-laws are not) and appear to have been included in norwegian canonical legislation sometime after 1152 (when nicholas breakespear, papal legate in scandinavia and later pope adrian iv, introduced the sixth cousin bans to norway/scandinavia). the penalties in these four norwegian law codes ranged from fines and having to do penance to the splitting up of the couple and even to banishment (“outlawry”).

in the 1270s, when magnus was “mending” all the laws in the country, the cousin marriage bans in norway were scaled back to the fourth degree (i.e. third cousins). this was a bit later than the rest of western europe where the cousin marriage bans were changed in 1215. for this reason, the author of the article suggests that the ban out to sixth cousins probably wasn’t ever strongly enforced in norway, since the authorities didn’t bother to update this regulation right away — like it was a sleeping law or something. that certainly might’ve been the case, and i tend to favor this idea actually. the sixth cousin ban was difficult to enforce right across europe — who knew who their sixth cousins were?! — which is why it was dropped after only a couple of hundred years or so (although thomas aquinas offered other theoretical reasons for scaling back the bans as well) — and i can’t imagine why the situation should’ve been any different in rather remote norway/scandinavia. on the other hand, perhaps the norwegian authorities just decided to hang on to these stringent bans for longer for whatever reasons. that certainly happened in neighboring sweden at the time of the reformation — unlike many of the other newly minted protestant/lutheran churches (as in the german lands, for instance) which did away with cousin marriage bans altogether, the swedish authorities made it difficult for most people to marry cousins right up until 1844.

whatever the case, marriages to closer than third cousins were banned in norway after the 1270s. how well these bans were enforced is, of course, another question. in all likelihood, like elsewhere in europe, enforcement probably became more rigorous and consistent over the course of the medieval period as christianity and the church and its norms permeated norwegian society. remember the example of the franks in the early medieval period: cousin marriage was banned by the frankish kings in the mid-700s, but it wasn’t until sometime in the 800s that the people began thinking that marrying a cousin was unseemly — and that someone ought to tell the bishop if the neighbor had! presumably there was a similar delay with cousin marriage bans gaining traction in norway (and everywhere else, for that matter).

all of this is assuming that the pre-christian norwegians married their cousins to some degree or another in the first place. i don’t know for sure or not if that was the case — Further Research is Required^TM — but it seems likely that the scandis would’ve behaved similarly to other germanic peoples who certainly did marry their cousins before conversion (see “mating patterns in europe series” below, esp. the posts on the germans and the anglo-saxons) — and they all shared similar kindred structures and feuding practices which seem to go along with cousin marriage, so….

there’s some evidence for a few norwegian christians here and there in the 900s, but the real push for conversion came with olaf ii who was king of norway in the early 1000s, so it’s more than likely that cousin marriage was present in norway right up until this point, although who knows what the frequency was.

one of the earliest — if not the earliest — introductions to norway of the crazy idea to ban cousin marriage at all probably happened in 1022 when the moster assembly (which looks to me to be in the gulatingslag) passed some ecclesiastical cousin marriage bans suggested by bishop grimketel (grimkell), english bishop of selsey. these were based on king æthelred‘s laws from the early eleventh century in which marriage to fourth cousins or closer was banned (this is news to me, btw!).

the arrival of christianity and cousin marriage bans, then, obviously occurred quite a bit later in norway than in the populations closer to the center of “core europe” — i.e. the franks (belgians and dutch) and the southeastern english — whose outbreeding projects were well underway by sometime in the 800s. the norwegians probably lagged behind in outbreeing by three or four hundred years, but, again, no idea exactly how much they’d been marrying their cousins beforehand. (similar case with the swedes.)
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a couple of other notes from the article not directly related to norway:

– sometime between 1161 and 1172, pope alexander iii gave dispensation to a certain group of people who were a part of the archbishopric of niðarós and who were having difficulties obeying the canon law banning sixth or closer cousin marriage. these people lived on an island “twelve days’ journey from Norway” and are believed by historians today to have been the residents of greenland! they were granted permission to marry their fourth, fifth, and sixth cousins. whew!

– the author of the article notes that the cousin marriage bans in iceland were probably never higher than the fourth degree (i.e. third cousins). in other words, icelanders never experienced the crazy bans out to the sixth cousins.

previously: inbreeding in sweden and inbreeding in 18th and 19th century sweden

_{(note: comments do not require an email. erroneous norwegian claim re. the paper clip!)}