consanguinity and polygamy

sean suggests that there is a correlation between consanguintiy and polygamy (or, rather, polygamy and consanguinity). i don’t know if anyone’s ever looked for a correlation between the two. if they have, i haven’t seen it. what someone should do is take the populations from consang.net (not the nations but the populations) and see if there is any correlation between consanguinity and polygamy or not. i’ve put that task on my “to do” list, but i can’t promise that i’ll get to it any time soon.

what i have done is check murdock‘s ethnographic atlas to see what sorts of societies (monogamous, occasionally polygamous, or polygamous) are also consanguineous (here consanguineous means first or second cousin marriage — i haven’t included uncle-niece marriages as that info is not available in the murdock atlas).

the cross tabs i used were DOMESTIC ORGANIZATION and NUMBER OF COUSIN MARRIAGES [Allowed]. the results are sorted into the following rows…

- Missing Data
- Indep. Nuclear Family – Monogamous
- Indep. Nuclear Family – Occasional polygyny
- Indep. Polyandrous Families
- Polygynous – Unusual Co-wives Pattern
- Polygynous – Usual Co-wives Pattern
- Minimal (stem) extended families
- Small extended families
- Large extended families

…and columns…

- Missing Data
- All four cousins
- Three of four cousins
- Two of four cousins
- One of four cousins
- No first cousins
- 1st & some 2nd cousins
- No 1st – 2nd unknown
- No 1st or 2nd cousins

i skipped the two “Missing Data” groups (fourteen results). i also skipped the “No 1st – 2nd uknown” group (twenty-seven results) since the presence or absence of second-cousin marriage was unknown. left out the polyandrous groups (all three of them), too. and i also drilled down (manually!) in the extended family categories (minimal/stem, small extended, and large extended) to check for consanguinity and polygamy there ’cause i couldn’t figure out how work that into the table (you’re welcome). i then combined all the monogamous, occasionally polygamous, and polygamous groups together (n=142 in total).

what did i find?:

well, for one thing, there’s a lot more polygamy and occasional polygamy out there in the world than monogamy, but then we all knew that already, didn’t we? there’s also more consanguineous marriage practices out there than not — or, at least, they’re allowed in more societies than not — but we’re all starting to know that now, too, aren’t we? (^_^) even in monogamous societies, there are twice as many that allow some form of cousin marriage (first or second) than those that don’t allow any.

the rate of consanguineous to non-consanguineous marriage allowed in monogamous societies is about 2:1. in polygamous and occasionally polygamous societies it’s about 2.5:1. so, yeah — there are more consanguineous marriages permitted in polygamous societies than monogamous ones, but is the correlation between the two (consanguinity and polygamy) very strong? i dunno. doesn’t really seem like it, but you tell me.

in Ya̧nomamö, chagnon suggests that groups that practice polygamy marry their cousins with greater frequency partly because the individuals in those societies have more cousins. he gives as example two ya̧nomamö extended families, one that had a founder with more wives than the other. because he founded so many lineages, as it were, the descendants of the guy with more wives were able to more easily find a cousin to marry simply because more persons who were their cousins existed. don’t know if this holds true for other polygamous groups, but it’s an interesting idea.

here are the numbers for you:

btw, the monogamous groups which allow(ed) cousin marriage are:

- the inca
- the badjau (pacific region)
- the burmese
- the romans
- the bribri (south america)
- the chinese (in chekiang)
- the tuareg
- the copper eskimo
- the lapps
- the iban (pacific region)
- the japanese (southern okayama)
- in the punjab (west)
- the vedda
- the yapese (pacific region)
- the manchu (aigun district)
- the kaska (north america)
- the toradja (pacific region)

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linkfest – 09/02/12

New DNA analysis shows ancient humans interbred with Denisovans – “A new high-coverage DNA sequencing method reconstructs the full genome of Denisovans — relatives to both Neandertals and humans — from genetic fragments in a single finger bone.” see also Genome Brings Ancient Girl to Life.

Monogamy and the Immune System – “[P]romiscuous mice had much more diversity in the genes related to their immune system.”

Why Humans Give Birth to Helpless Babies – metabolic crossover, not bipedalism.

Vitamin D may increase IVF success – depending on race – “[W]hile white women can boost their IVF success rates with vitamin D, the opposite appears to be true for Asian women.”

At Last, Humans Get a Scientific Promotion – as opposed to a copernican demotion. (~_^) – from matt ridley.

Another Tale of Two Maps – “In accordance with my Pioneer Hypothesis, fertility rates in Europe and East Asia are low because these regions are populated by people who do not descend from recent immigrants, having inhabited these areas since ancient times by in large. Hence, natural selection has favored slowly reproducing individuals (who are only marginally ‘natalist’ to even ‘anti-natalist’), to keep population under control.” – from jayman.

Wealthy families obey economics rather than evolution – “A study in Sweden spanning five generations confirms that the wealthiest families tend to remain small, despite evolutionary pressures to have as many offspring as possible…. Evolutionarily, the model might only apply in safe countries like Sweden, which has one of the longest life expectancies in the world….”

National differences in female partner violence – “Ethiopia has the highest percent ever being physically or sexually assault by a partner — 71 percent. Japan has the lowest with 15 percent.” – from the inductivist.

Republican men are the most politically informed – from the awesome epigone.

Analysis explores how religion and ethnicity shape the Asian-American vote – “Asian Americans who are agnostic, atheist, Hindu and Muslim were more likely to hold liberal political views and were more likely to vote for Obama. Protestants and Catholics who were more likely to hold politically conservative views also supported Obama. Vietnamese Americans, many of whom are Catholic, were more likely to vote for John McCain.”

Addicted to the internet? It could be all in your genes – ruh roh.

Severe Diet Doesn’t Prolong Life, at Least in Monkeys – eat up!

A Turkish origin for Indo-European languages – “Languages as diverse as English, Russian and Hindi can trace their roots back more than 8,000 years to Anatolia….”

bonus: Horse gait traced to single mutation – “A single gene mutation in horses can endow them with a wider repertoire of gaits. The finding, reported this week in Nature, shows that some seemingly complex physical traits can have a simple genetic basis.”

bonus bonus: China’s Chaotic Health Care Drives Patient Attacks

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monogamy, serial monogamy, and polygamy

laura betzig makes a convincing argument that, especially for the elites — both secular and clerical (think popes and bishops) — marriage in medieval europe might have been monogamous, but mating wasn’t. not only were the elites not all that monogamous in their mating practices, many of them were also incestuous [pgs. 185-86]:

“In the same vein — and maybe richest of all accounts — is Lambert of Ardres’ ‘Historia comitum Ghisnensium,’ the early thirteenth-century pean to his benefactor, Count Baudouin. Marc Bloch calls Baudouin ‘hunter, toper, and great wencher’ (1961, p. 104), and Georges Duby has made a lot of the last. As he puts it: ‘Life in a noble household was a hotbed of sex’ (1983, p. 70). Or, as Lambert says: ‘”From the beginning of adolescence until his old age, his loins were stirred by the intemperance of an impatient libido…; very young girls, and especially virgins, aroused his desire”‘ (Duby 1978, p. 93). Roissy Baudouin and his kinsmen are said to have preferred pretty women; no matter how casually sexually encountered they are all described as ‘beautiful.’ And, evidently, fruitful: This count was buried with twenty-three bastards in attendance, besides ten living legitimate daughters and sons (p. 94).

“Even these might have been just the fruits of the family tree’s primary limbs. As Lambert notes, Baudouin by no means kept account of all his bastards. These were usually scattered far and wide. And, as Duby notes, noble men would just as soon have the ignoble women — the servants, slaves, and whores — who begot so many of them. The lovers noble men did remember may have included their vassals’ daughters, ‘but there is more evidence that they were the family’s bastard daughters, who formed a kind of pleasure reserve within the house itself’ (Duby 1978, p. 94). This kind of sex was, then, endogamous. Noble or half-noble women begat noble or half-nobel children, ad infinitum. ‘Illegitimacy was a normal part of the structure of ordinary society — so normal that illegitimate children, especially males, were neither concealed nor rejected’ (Duby 1983, p. 262). They always had the right, at least, to bed and board in their father’s house. ‘That house was always open to them’ (p. 263.) Bastards like these, the cream of the illegitimate crop, are most likely to have made up the twenty-three who watched when Baudouin was interred.”

so, not a big surprise, powerful men in the middle ages tried to maximize the number of offspring they had. and they even mated somewhat incestuously sometimes.

this made me wonder how different marriage or mating patterns affect relatedness within a society — apart from mating with relatives or not, that is. i mean: how does monogamy or polygamy affect the relatedness between the members of a society?

so, forget about cousin marriage and all that jazz for a second. here’s what strict monogamy looks like (think christian europe). (yes, i know there’s always a little hanky-panky — the milkman and mrs. jones, for instance — this is just schematic.):

first of all, triangles are men and circles are women. i colorized only the men ’cause it just got too confusing to colorize everybody. the women have been numbered instead. the point is that, here in strict monogamy land, there are six men and six women, none of whom are related, who marry/mate, and each pair has two kids. each pair of kids, then, (barring any hanky-panky) is related to their parents and each other, but not to anybody else in their society. each little nuclear-family is a discrete, “atomized” group. (this isn’t completely the case in a real population, of course. in every natural society, the members are related somehow, even if it’s distantly.)

in contrast, polygamy narrows the gene pool since one man can have several wives. thus there are several sets of half-brothers and half-sisters within polygamy land who are (obviously) all related to one another (think arab and many african countries). and some men fall out of the gene pool altogether. here mr. green marries contestants women numbers 3, 4, 5 and 6, while messrs. red, orange and yellow are out of luck:

so, with polygamy, the gene pool within a society narrows. in reality, what typically happens, at least in arab/muslim societies, is that the polygamy occurs frequently within the extended family, so that the gene pool narrows even more within the extended family. the other thing that often happens — particularly in arab countries — is that there is a lot of divorce, so in reality you have something like a serial monogamy, only it’s a serially polygamous society.

(whew! this is gettin’ complicated. *hbd chick wipes brow*)

finally, serial monogamy (think the amhara of ethiopia — or modern western society):

here in my schematic serial monogamy land, each of the men has married twice to two different women and has had one kid with each of them. so, each kid has one half-sibling via his father AND one half-sibling via his mother. so, the relatedness is not quite as narrow as in a polygamous society (every man does get to produce offspring) — but at the same time, there are more genetic connections between the members of the society than in a strict monogamy. (in reality, serial monogamy is often more like polygamy since many women vie for the chance to mate with the best men, while the whiskeys of the world are left out in the cold.)

in strict monogamy, in the second generation, each child shares (probably) 50% of their genes with their one and only sibling. in serial monogamy, each child shares (probably) 25% of their genes with two siblings. the connections look like this (plus the kids of mr. blue and mr. yellow at the ends are also related):

complicated, huh?

(btw — in polygamy, each child shares (probably) 50% of their genes with the sibling with whom they share a mother, and (probably) 25% of their genes with their half-siblings via their father.)

so, if we recall again that in a natural population the members of a society do, of course, share a lot of genes in common, then we can see that a strict monogamy would keep the genetic ties between non-family members “broad but shallow”; a population practising serial monogamy has somewhat narrower and deeper genetic ties between non-immediate family members, i.e. extended familiy ties within the society are stronger; and polygamy leads to narrow and deep genetic ties within the extended family, which becomes somewhat cut-off from the larger society. (this is even more so the case when you recall that cousin-marriage is common in polygamous societies.)

i think that the coporate and individualistic nature of western europeans (especially the english!) is connected to the (somewhat) strictly monogamous, non-cousin marriage mating patterns which have been around since the early medieval period in much of europe. these mating patterns set the stage for the selection of certain personality traits — individualism + clark’s traits — since western european families were mostly discrete and independent units making their own way in the world. these traits made western european man what he is today was yesterday.

the fact that europeans (including those of us in the u.s., australia, etc.) are now adopting serial monogamy must mean big changes are in store.

edit: boilerplate and boilerplate 2.0

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