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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finding hbd chick 2014

here’s a map of where this year’s visitors to the blog were located. i am happy to report that i achieved my goal for 2014 and had one visitor (one page view) from turkmenistan, so…woo hoo! (~_^)

visitors 2014 - map - turkmenistan

here are the top 20 countries in descending order. the difference between the u.s. and the u.k. is still roughly one order of magnitude. for the wiseguy (krakonos! =P ) who last year asked what the figures were per 100,000 people, total unique visitors from the u.s. for 2014 was 75 per 100,000 — for the u.k., 59 per 100,000 — for the czech republic, 17 per 100,000. (^_^) (note that these are just wordpress stats, so they’re not the greatest.)

germany, france, and spain moved up in the rankings, and south africa is now in the top 20 (hello south africans!). belgium and the czech republic dropped out of the top 20. =(

– united states
– united kingdom
– canada
– australia
– germany
– sweden
– france
– ireland
– finland
– norway
– india
– brazil
– spain
– netherlands
– new zealand
– poland
– austria
– denmark
– greece
– south africa

the top 10 referrers (not including search engines) in order were…

– twitter
– jayman
– steve sailer
– heartiste
– neorxn.com
– slatestarcodex
– unz.com
– mr. mangan, esq.
– vdare.com
– captaincapitalism.blogspot.com

…thank you gentlemen and twitterheads! (^_^)

and here are the totally relevant and/or…interesting…search engine searches via which people arrived on the blog:

– pirates (got ’em)
– black american porn (don’t ask)
– european tribes (yup!)
– hajnal line (oh, yeah)
– hodor (hodor!)
– where does culture come from (srsly. where does culture come from?)
– giant sloth (apparently!)
– hbd chic (très chic)
– great tits (shhhhhhhh!)
– do gypsies marry their cousins (yes)
– dinosaur head dress (d*mnit! forgot to cover that this year AGAIN.)
– right wing authoritarianism test (covered)
– cousin marriage in japan (yes and yes)
– left-wing authoritarians were found in eastern europe (you know it!)
– maniots (love the maniots!)
– geographical origin of quakers (glad you asked!)
– inbreeding in sicily (yeah, lots of it)
– double first cousin (yes, there is such a thing)
– game of thrones and actual history and frisia (GoT and history — there’s a book about that; and here’s a post on frisia)
– where are my dragons (when IS GoT coming on again?!)
– irish travellers consanguinity history (here)
– what does a lemur look like (eh?)
– horse japanese art (i like it!)
– what country is above scotland (uhhhh…)
– good morning penguins (penguin alerts!)
– inside the hbd cult (no)
– all grandmas are created equal (no, they’re not.)
– who is hbd (i think you meant what)
– scandinavian black magic witches bullet (whoa)
– i was born in the potteries am i a northerner (dunno. i am a northerner! (~_^))
– boinking sisters (no, no, no. that’s just WRONG!)
– if father younger brothers daughter marry with father son for muslim (uh…yes. i think.)
– the hbd chick (thank you for the definite article!)
– do plants have anuses (wait. what?)

THANKS AGAIN EVERYBODY FOR ALL OF YOUR INFORMATIVE AND THOUGHTFUL COMMENTS AND INPUT! (^_^)

more next year!

previously: finding hbd chick 2013

fbd cousin marriage and clans and tribes in iraq

the counts vary depending on who you talk to and how you want to slice up clans and tribes, but there’s something on the order of 150 tribes comprised of ca. 2,000 clans in iraq today (“today” meaning in 2008). roughly three-quarters of the iraqi population admits to belonging to clans and/or tribes. here’s a map of where the tribes are located (from same report as above – click on map for LARGER view):

iraq - tribes

consang.net puts the cousin marriage rates for iraq at anywhere between 25 and 53% in the 1980s and 2000s [pgs. 17-18 – pdf], and those numbers include a lot of double-first cousin marriages which indicates father’s brother’s daughter’s (fbd) marriage. a 50% cousin marriage rate would be one of the highest rates in the world, comparable to places like saudi arabia and pakistan (and certain neighborhoods in bradford).

a 2005 u.n.-funded report from the iraqi ministry of planning and development cooperation [pdf – pg. 47] tells us that, in 2004, seventeen percent of all married women were in fbd marriages (the report refers to them as father’s brother’s son or fbs marriages taking the point of view of the woman — same difference), another four percent were in father’s sister’s daughter (fzd) marriages, and another thirteen percent were to some other kind-of relative within the paternal clan. that’s 34% of marriages between paternal relatives. another fifteen percent of marriages were between maternal relatives — maternal cousins and such. fbd marriage has actually decreased in frequency since the 1940s, but other forms of cousin marriage increased over the same time period. as the report says [pg. 48]:

“Thus, in contrast to patterns among other populations in the Middle East (Patterson 2002), kin marriage frequency does not seem to have decreased with the overall modernisation of Iraq.”

the direct result of all this fbd marriage, i think, is the hierarchical structure of arab/iraqi society in which extended families are nested into sub-clans which are nested into larger clans which, in turn, are nested into tribes — and all of these are based on a patrilineal system. this structure means that subgroups can and do easily fission off from their fellow subgroups and that they don’t always naturally cooperate with one another. this is where the bedouin “I against my brother, my brothers and I against my cousins, then my cousins and I against strangers” principle comes in. from murphy and kasdan’s “The Structure of Parallel Cousin Marriage” [pg. 24]:

“Degree of relationship is the significant criterion in the determination of allegiances. Distance from a common ancestor in terms of numbers of intervening kinsmen is crucial to the ordering of relations within and between agnatic sections, and the principle of degree of relationship determines the composition of the Ego-centered blood responsibility group.

“[This] fact tells us a great deal about the patrilineal units of Arab society: except perhaps at the level of the tribe, there are no lineages in the sense of bounded groups having a continuing and cohesive base in corporate rights and duties. Differing degrees of relationship within the named groupings tend to break up their internal homogeneity; they are not solidary units, but become activated only temporarily at the call of political expediency….

it’s difficult to next to impossible to form “corporate” cooperative groups like those you find in northwest european societies in fbd marriage societies, because it just doesn’t pay — in inclusive fitness terms — for individuals to cooperate with distant relatives, let alone strangers. or maybe the way to look at it is that, given the degrees of relatedness between family members in such populations, which are way higher than in non-cousin marrying pops, it just pays more for individuals to cooperate with the closest relative(s) possible in any given situation. see steve sailer’s “Cousin Marriage Conundrum” for more on the dynamics of fbd societies.

this is not something automatic or something that can be changed overnight. if you were to take a group of long term outbreeders — like northwest europeans — and set them to marrying their cousins, they would not begin to behave like clannish, nepotistic inbreeders in one generation. i don’t think. we’re probably talking about an evolutionary process here, so you’d have to let a little natural selection take its course. you’d have to allow for the relatedness between individuals in the population to change and for the dynamics within the society to change — in other words for the selection pressures to change — until more clannish individuals began to show higher fitness rates and increased in number in the population.

and vice versa for changing a long term inbreeding society.

as greg cochran has said, “every society selects for something.” i think a long term inbreeding society selects — or can select — for what i call clannishness. and iraqis have got that in spades. they’ve got clans and tribes, nepotism, and an obvious inability to handle liberal democracy. not that that’s some sort of goal in and of itself. i’m just sayin’.

so the degree and the type of inbreeding or outbreeding in any population is important — i.e. the percentage of cousin marriages, for instance, which we’ve seen is high in iraq, and whether or not those cousin marriages are fbd in type which leads to increased amounts of the very close double-first cousin marriages — but so is the length of time of the inbreeding or outbreeding. the question then is: for how long have iraqis been marrying their cousins, in particular their fbds?

in “Parallel-Cousin (FBD) Marriage, Islamization, and Arabization”, andrey korotayev points out that fbd marriage is found almost exclusively in those areas of the world that were a part of the eighth century caliphate (one exception seems to be the sotho-tswana peoples of southern africa):

caliphate in 750

korotayev suggests, rightly so i think, that the arabs introduced fbd marriage to populations in the maghreb, mashriq, and south asia (afghanistan and pakistan). the locals picked up on fbd marriage as part of a broader arabization process — they were just generally keen to imitate their new overlords in all ways. (btw, pseudoerasmus is on a mission to figure out why any group would adopt fbd marriage at all. most peoples consider it too incestuous [it does lead to a lot of double-first cousin matings], so keep an eye out on pseudo’s blog for more on that!)

the arabs conquered iraq (as part of their conquest of the persian sasanian empire) in the early part of the 600s, so that’s a good 1400 years of possible fbd marriage in iraq, although it no doubt took some time before the local population adopted the practice in significant numbers. it’s worth noting that this is pretty much diametrically opposed to what happened in europe where cousin marriage of all sorts began to be banned right around the same time.

question is, were the peoples of iraq marrying cousins of any sort before the arabs arrived? my guess is that they were not marrying their fbds before the arabs arrived, and, going by the below description of the aramaeans (which is just hearsay, i’ll admit), many of them may not have been marrying their closest cousins much at all. (of course, the elite persians — the zoroastrians — were marrying their siblings, but that’s another story for another day.) from Iraq After the Muslim Conquest, here’s what the arabs thought of the aramaeans [pg. 179]:

For their part, Arabs tended to stereotype Aramaeans as arrogant people who identified themselves by their place of origin instead of by a tribal genealogy. Arabs looked down on them as people who had lost their power and independence first to Persian and then to Arab rulers. According to Mas’udi, the Anbat were inferior to Arabs because the latter were granted a prophet and the former were not.”

inbred, clannish peoples tend to identify themselves by some sort of family name or at least by the names of their fathers and grandfathers — think: arabs, chinese, russians, scots. it’s outbred peoples who often take other sorts of surnames — like all the “professional” names of the english (miller, cooper, sawyer, lawyer, archer!). many northwest european groups have this, of course. so it’s interesting that the aramaeans did not identify themselves according to tribe but according to place. this might indicate that they were not regular inbreeders, but Further Research Is RequiredTM.

btw, here’s what the aramaeans thought of the arabs:

“On their side, the Aramaeans, as representatives of a sedentary, orderly, agricultural population, reacted somewhat unfavorably to what was felt to be an impetuosity or excitability on the part of Arabs. This attitude and the stereotpe it involved is well illustrated in the case of an Arab monk from Hira named Mar Eliyya who lived at the Nestorian monastery on Mt. Izla above Nasibin in the late sixth century. The monastic chronicler who described Rabban Eliyya’s energentic response to a crisis in the community found it necessary to explain that he possessed the ‘violent character of the bedouin.’ Such attitudes survived the conquest and were expressed as a feeling of superiority on the part of the Anbat over Arabs because of the achievements of the Babylonians, the antiquity and spread of their civilization, the flourishing of agriculture, and their acceptance of Islam without having a prophet appear amongst them.”

here’s more from Iraq After the Muslim Conquest [pg. 236]:

“The single most important ethnographic change in seventh-century Iraq was the arrival of large numbers of Muslim Arabs from the Arabian peninsula and the foundation of new urban centers as garrison cities where they settled….”

the author, historian michael morony, goes on to describe the settlement patterns of the invading arabs in two cities, kufa and basra — the arabs had gated communities and everything! [pgs. 242-243, 246]:

The pattern which emerges at Kufa is that of a city divided into separate tribal districts (Ar. sg. *nahiya* or *mahalla*), each with its own *masjid* for daily worship and tribal assemblies, its own cemetery, and with gates to close off the streets going through each district. Within each district, the members of the respective tribes seem to have settled by clan along lanes or alleys adjacent to the main street of the district. From a purely descriptive point of view, it is possible to identify most of the tribal districts in seventh-century Kufa….

“It also seems that as time passed, subgroups within a tribal district tended to form their own neighborhoods. Such were the districts (*mahallat*) of the Banu Shaytan clan of Tamim and of the Banu ‘Anz ibn Wa’il, who had their own *masjid*….”

“The organization of Basra along tribal lines was similar to that of Kufa….”

another city, hira, had been heavily settled in by arab traders for generations before the arab invasions, and they, too, had lived in neighborhoods arranged according to clans/tribes, so the clan system obviously goes well back in arab society [pg. 221]:

“Hira was the political and cultural hub of this zone of Arab settlement and, in spite of the presence of Persian soliders and *dahaqin*, it was considered to be an Arab city. The Arab population of Hira was a mixture of many small groups of diverse tribal origins. Members of Tanukh, Tayyi’, Tamim, Sulaym, ‘Ijl, Shayban, Tha’laba, Asad, Azd, Kalb, and others could be found at Hira. The organization of late Sasanian Hira around several fortified enclosures (Ar. *qusur*) that were identified with particular clans, the existence of tribal churches, and the political and social domination of the town by an elite of notables (Ar. *ashraf*) belonging to the leading clans make Hira a good example of a late pre-Islamic Arab city as well as a prototype for tribally organized early Islamic cities such as Kufa and Bara.”

more from morony [pgs. 254-255]:

One of the most apparent social consequences of the conquest was an extension of tribal social organization, especially in urban settings. This was associated with the new ruling group and was partly the result of the cohesion of tribal groups, which preserved their identities in the garrison cities and even enhanced their ties to other groups on the basis of nominal kinship. The state also helped to preserve such identities by using them as a basis for military organization. An equally powerful influence in the survival of tribal society, however, was the Qur’an. It sanctioned many aspects of the tribal social ethic, such as the importance of group solidarity, joint responsibility, exemplary behavior, generosity, hospitality, the protection of the weak by the strong, raiding, and retaliation. Although the intention in the Qur’an was to replace tribal identities with an Islamic identity, many tribal social values received a new religious sanction in the process.

Retaliation is a good example of the survival and reinterpretation of the tribal ethic in early Islamic Iraq. The Qur’an sanctioned the principle of retaliation partly because it was impossible to suppress it completely and partly because the early Islamic community at Madina faced a desperate struggle for survival. But the Qur’an also attempted to prevent an unending chain of blood vengeance by recommending charity, forgiveness, and the acceptance of a blood-price (Ar. *diya*) as the better way.

“The annals of early Islamic history are full of examples of retaliation, and there is no question that it remained one of the most important responsibilities of kinship. Of greater significance are the attempts by the state to restrict and to control it. When two of Muthanna’s lieutenants drowned several members of the tribes of Taghlib and Namir at Siffin [in syria-h.chick] in 634 in retaliation for a pre-Islamic grievance, ‘Umar made them swear that they had done it as an example and not out of vengeance. Under Mu’awiya the state attempted to regulate the operation of the private blood-feud in Iraq by enforcing the responsibilities of the clan (Ar. *aqila*) as a legal unit. At Basra, Ziyad held families and tribes responsible for the behavior of their members. Payment of the blood-price was assured by deducting the amount from the pay of the guilty party or from that of his tribe. If the victim was non-Muslim, half the normal blood-price went to the next of kin and the other half to the state treasury….”

so the invading arabs introduced — directly transplanted, really — into seventh century iraq tribes and tribal behaviors, including blood feuds, along with their underlying foundation, fbd marriage. i’m not sure what the social structures of pre-islamic iraq were like, but from what morony says, it sounds as though the arab-style of tribalism was a new introduction at the time to the region.

divisions within pre-islamic iraqi society had, however, been growing in the late sasanian era, and these divisions were not at all discouraged by the arabs once they took charge [pgs. 518 and 278]:

One of the most important of such trends was the formation of a society composed of religious communities, which was already well under way by the late sixth century with the strengthening of internal bonds and external boundaries….

“[T]he Muslims expected Jews and Christians to live according to their own religious laws, so the conquest had the effect of encouraging the operation and continuing development of autonomous systems of religious laws….”

“[T]he formation of…closely knit communities increasingly isolated the members of one group from those of another. The boundaries created between religious groups by separarte bodies of law are indicative of the rising barriers to interfaith relations at the end of the Sasanian period. The defensiveness associated with this development was symbolized by a shared vocabulary of protective walls. The Magians [zoroastrians-h.chick] saw the good fortune of their religion (M.P. *den x’arrah*) as a fortress-like enclosure formed by the starry band around the sky, which protected the good from the attacks of demons. Jews spoke of making a fence around the Torah, and the Nestorian synod of 554 called the canons ‘high walls, impregnable fortresses, protecting their guardians against all danger.'”

so, it’s not as though pre-islamic iraq was a unified nation, either. yes, my curiosity has been raised, so i’ll be checking into all of this further.

iraqis have been working on being highly clannish and tribal for nearly 1400 years, if not longer. my conservative guesstimate is that they’ve been practicing the closest form of cousin marriage possible — fbd marriage — for a thousand years, again if not longer. that’s about 40 generations, if we count a generation at 25 years in length.

like super misdreavus tweeted, there’s no reason to think that simply introducing western institutions to the country will change how the country works. not overnight. not even in ten or twenty generations, if the new institutions could somehow be sustained for that long in the country. saddam hussein tried to suppress the clans and tribes — he apparently banned the use of tribal names [pg. 3] — as did gaddafi in libya, but to no avail. iraq’s solutions lie in that country’s own traditions — their own methods of governing and running things — not in western style democracy.

as super misdreavus also tweeted, remember that “hbd denial costs human lives.” i sincerely wish — for the sake of the people in iraq, for the sake of everyone — that people would wake up to this fact.

(note: comments do not require an email. erbil, iraq – inhabited for 8,000 years.)

consanguin-eous marriage in afghanistan

just for a change of pace.

the consanguineous (second cousin or closer) marriage rates in afghanistan are high. consang.net tells us that the rate is between 40 and 49%. more details are to be had in Consanguineous Marriages in Afghanistan (2012) and Prevalence of Consanguienous Marriages in West and South of Afghanistan (2012), including consanguinity rates by province and ethnic group.

back in the 1970s, joseph westermeyer found that peoples in southeast asia had different mating patterns depending on what elevation they lived at — the higher up, the closer the mating patterns (see also here). this pattern appears to be holding true wherever i look (example) — and now we have afghanistan.

here’s a map of the mean inbreeding coefficients for the provinces studied in the two papers above — higher coefficients indicate greater inbreeding (click on map for LARGER view):

Afghanistan provinces - inbreeding coefficients - colored

aaaaand here’s a topographical map of afghanistan. elevation and inbreeding look to match pretty closely (would be nice to have data from the other provinces, too):

Afghanistan_Topography

here’s a breakdown of consanguinity rates by ethnicity in the country. the numbers are also sorted here by region depending upon which paper they came from — the first paper dealt with the north and east of the country, the second with the south and west. remember that consanguineous marriages include: double-first cousin marriage, first cousin marriage, first cousin-once-removed marriage, and second cousin marriage:

– north & east –
Turkmen = 48%
Hazara = 47%
Uzbek = 44%
Pashtuns = 43%
Tajik (Shi’a) = 43%
Tajik (Sunni) = 38%

– south & west –
Turkmen = 64%
Hazara = 53%
Sadats = 51%
Tajik (Sunni) = 51%
Pashtun = 50%
Tajik (Shi’a) = 49%

the turkmen in the lead!

interestingly, while there is more consanguineous marriage in the south and west of afghanistan, the inbreeding coefficients are higher in the north and east of the country, indicating that there are greater amounts of closer marriages in those (high elevation) regions. and this does appear to be the case — the percentages of double-first cousin marriages are higher in the north and east:

– north & east –
Turkmen = 8.7%
Pashtun = 7.9%
Uzbek = 7.5%
Hazara = 6.4%
Tajik (Sunni) = 6.3%
Tajik (Shi’a) = 4.0%

– south & west –
Sadats – 3.0%
Pashtun – 2.3%
Tajik (Shi’a) – 1.8%
Hazara – 1.2%
Turkmen – 1.2%
Tajik (Sunni) – 1.1%

i’m going to guess that there’s more father’s brother’s daughter’s (fbd) marriage in the north and east of afghanistan rather than in the south and west, since fbd marriage tends to push towards greater amounts of double-first cousin marriage (and, therefore, greater inbreeding in general). i’m also going to guess that the tajiks really don’t practice much fbd marriage at all, either in the north or the south — except maybe for the sunni tajiks in the north.

how long have the various afghani populations been marrying their cousins? dunno. long time prolly. fbd marriage was most likely introduced to the region by the arabs, so the afghanis probably adopted that form of cousin marriage sometime after the mid-600s.

previously: this one’s for g.w. and the flatlanders vs. the mountain people and kandahar vs. levittown

(note: comments do not require an email. turkmen girl & baby in afghanistan.)

why mbd marriage amounts to less inbreeding than fbd marriage

in response to my post on why fbd marriage amounts to more inbreeding than mbd marriage (short answer: it results in more double-first cousin marriages), violet asks:

“I don’t understand why there can’t be double first cousins with mbd.”

good question. well, there certainly can be double-first cousin marriages in mbd societies, it’s just that the structure of mbd marriage doesn’t give the same push towards double-first cousin marriage as fbd marriage does.

what i should’ve done in the previous post on fbd (father’s brother’s daughter) marriage was to include diagrams of mbd (mother’s brother’s daughter) marriage along with the diagrams of fbd marriage, but to be honest i just got lazy (sorry!). so, without further ado, here is mbd marriage (you might want to have open the fbd marriage post at the same time):

ego (red triangle guy) marries his maternal first cousin, i.e. his mother’s brother’s daughter (mbd).

but who does ego’s brother (the triangle to the right of ego) marry? if he lives in a society in which mbd marriage is favored (china, for instance), and if there’s a female maternal cousin available, he’ll marry her (maybe/probably). in this case, that’s ego’s wife’s sister:

then what? well, in the next generation, unlike in fbd marriage, the kids of ego and his brother should NOT marry each other. the kids should marry their mothers’ brothers’ kids:

these kids are all first cousins, but they’re not double-first cousins (unlike in the fbd marriage scenario). the four kids do not share both sets of grandparents in common, whereas double-first cousins do.

also, you can see that there’s an additional party brought into this family tree — the yellow mom/aunt. she is not from ego’s patrilineage. she’s an outsider to some degree or another, and these wives that are brought in from the outside are why mbd marriage is often described as alliance building — different patrilineages build ties with one another.

so, the mbd marriage system doesn’t have the same push towards double-first cousin marriage as an fbd marriage system does. you can see this (i think) if you browse through the consang.net tables — there are more incidences of double-first cousin marriages recorded in fbd societies (arabs et al.) than in mbd societies (just about everybody else).

the reason any of this is good to know is because it is important to bear in mind that not all cousin marriage systems are the same — some result in more inbreeding or closer genetic relatedness between family members than others — and that should affect the evolution of “genes for altruism/other innate social aptitudes” in these populations.

previously: why fbd marriage amounts to more inbreeding than mbd marriage and tribes and types of cousin-marriage

(note: comments do not require an email. contrarian!)

why fbd marriage amounts to more inbreeding than mbd marriage

*update 07/09 – see bottom of post.*

i keep saying that father’s brother’s daughter (fbd) marriage — the favored type in the arab world — amounts to greater inbreeding than mother’s brother’s daughter (mbd) marriage — the usual type almost everywhere else (including china) — but i haven’t been able to put my finger on exactly why.

i showed before that fbd lineages fold back in on themselves while mbd lineages draw in new brides from other lineages. now i finally figured out exactly what’s so inbred about fbd marriage:

because it leads to more double-first cousin marriages, and double-first cousins share, on average, more genes with one another than first cousins.

*****

first, some illustrations.

here is fbd marriage:

ego, who is a guy of the male persuasion, marries his paternal first cousin, i.e. his father’s brother’s daughter (fbd). ok? ok.

but who does ego’s brother (the triangle to the right of ego) marry? if he lives in a society in which fbd marriage is favored (anywhere in the arab world, for instance), and if there’s a female paternal cousin available, he’ll marry her (maybe/probably). in this case, that’s ego’s wife’s sister:

then what? well, in the next generation, the kids of ego and his brother should also marry each other, continuing the fbd marriage tradition:

and those kids are not just first cousins but double-first cousins because, not only are their fathers brothers, their mothers are sisters. they share both sets of grandparents in common. if you think about you and your first cousins, provided you’re not from a society where fbd marriage is the norm, then you only share one set of grandparents with your first cousins.

in societies where fbd marriage is preferred, there must be an increase in the number of double-first cousin marriages compared to other cousin marrying societies. it’s not something that happens one hundred percent of the time, but it must happen more than it would have if fbd marriage wasn’t preferred because there is this push to marry within the patrilineage.

*****

and now for a little math (a very little, i promise you!).

first cousins have an inbreeding coefficient of 0.0625. double-first cousins, 0.125.

imagine two societies, A and B — and in each of these societies, half of the marriages are between first cousins (consanguinity rate = 50%) — but in society A, all of the cousin marriages are between first cousins, while in society B, all of the cousin marriages are between double-first cousins. then we wind up with different coefficients of inbreeding for each of the populations:

society A: 0.50 x 0.0625 = 0.03125
society B: 0.50 x 0.125 = 0.0625

society B is more inbred (has a greater coefficient of inbreeding) than society A because of all the double-first cousin marriage.

so, if you look at the consang.net data, for example, china today has a cousin marriage rate of ca. 5%, while syria has a rate of ca. 31.6% (per woodley and bell). that’s a substantial difference in the amount of cousin marriages between the two nations; BUT, 7.8% of marriages in syria are between double-first cousins, so there is an even greater difference in the degree of inbreeding between the two countries than one might first suppose.

*****

so, not only does the arab world have more cousin marriage than most other societies today, it also has a more inbred form of cousin marriage than everyone else. although it doesn’t occur in arab societies one hundred percent of the time, the higher frequency of fbd marriages in those populations must make the arab world potentially even more inbred than populations with no tradition of fbd marriage.

note that mother’s sister’s daughter’s (mzd) marriage ought to be as similarly inbred as fbd marriage — it’s the mirror image of fbd marriage. mzd marriage occurs occasionally here and there, but it is not a favored type of cousin marriage anywhere that i know of. wrong! wrong, wrong, wrong. (thnx, wilhelm!)

update 07/05: see also why mbd marriage amounts to less inbreeding than fbd marriage

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inbreeding and the evolution of altruistic behavior ii

in Understanding Human History, michael hart did a real nice job of explaining how kin selection or inclusive fitness works and how “genes for altruism” could be selected for [pgs. 37-38]:

“For about a century after Darwin proposed his theory of evolution, the origin of altruistic behavior in animals remained a puzzle. It was not until the 1960s, when William D. Hamilton proposed his theory of kin selection, that a satisfactory explanation was given. That theory can perhaps best be explained by an example:

“Suppose a man sees his identical twin drowning in a river, and estimates (correctly) that if he were to jump in and try to save his brother the probability of success would be 80%, while the probability that he would die in the attempt would be 20%. Consider these two alternatives:

“a) Some of the man’s genes strongly dispose him to rescue his brother, and he therefore jumps in and tries to save him (‘altruistic behavior’).

“b) The man does not have genes that dispose him to rescue his brother, and he therefore stays on the shore and lets his brother drown (‘selfish behavior’).

“In case (b), exactly one copy of the man’s genes survives, and may later be replicated. However, in case (a), if the rescue attempt is successful, two copies of the man’s genes survive (one in his own body, one in his brother’s). As this will happen 80% of the time, on average 1.6 (= 0.80 × 2) copies of the man’s genes will survive. In this situation, therefore, genes that dispose a person to altruistic behavior will — on average — have more surviving copies than genes that dispose a person to act selfishly and will be favored by natural selection.

“Now consider a slightly different example. Suppose that the man on shore is a brother — but not a twin — of the person who is drowning. Case (b) will still result in one copy of his genes being preserved. However, since ordinary siblings share only 50% of their genes, if the man on shore succeeds in rescuing his brother then (on average) 1.5 copies of the man’s genes will survive. Since 80% of the attempts will be successful, case (a) will on average result in 1.2 (= 0.80 × 1.5) copies of the altruistic genes surviving. Since 1.2 is greater than 1.0, the altruistic genes will be favored by natural selection in this case too.

“Suppose, however, that the two men were not brothers, but merely first cousins. First cousins, on average, share only one-eighth of their genes. In this case, altruistic behavior results in only 0.9 (= 0.80 × 1.125) copies of the man’s genes surviving, and natural selection will therefore favor the genes for selfish behavior.

“The upshot is that a gene that disposes its bearer to behave altruistically toward a close relative can have a selective advantage over one that disposes its bearer to act completely selfishly. Furthermore, this can occur even though the relative never returns the favor, and even if the survival of the relative does not increase the group’s chances of survival. It is not necessary that either reciprocal altruism or group selection operate for kin selection to result in the spread of genes that dispose their bearer to act altruistically toward close relatives.”
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what’s missing from these examples is, of course, inbreeding. and depth of time.

take michael’s second example up there…

“Suppose that the man on shore is a brother — but not a twin — of the person who is drowning.”

…but let’s add that the parents of these brothers were first-cousins. that makes these two guys: brothers AND second-cousins (i.e. the children of two first-cousins). so they probably share not only 50% of their genes in common as brothers, but also 3.13% of their genes in common as second-cousins. so the “push” to jump in the water to save the brother/cousin must be somewhat stronger in the inbred pair than for the brother to save just a plain ol’ brother.

now let’s take this example of michael’s…

“Suppose, however, that the two men were not brothers, but merely first cousins. First cousins, on average, share only one-eighth of their genes.”

…but let’s make them double first-cousins rather than just first-cousins. what happens then?

well, while first-cousins probably share 1/8th or 12.5% of their genes in common, double first-cousins share … well, double that! … or 1/4 or 25% of their genes in common.

what happens to michael’s calculation then?

“In this case, altruistic behavior results in only 0.9 (= 0.80 × 1.125) copies of the man’s genes surviving, and natural selection will therefore favor the genes for selfish behavior.”

in the case of double first-cousins the calculation becomes 0.80 x 1.25 = 1.0. that’s just breaking even using michael’s example, but what if the odds of saving the cousin from drowing are better than 80%?

or what about the depth of time i mentioned above? what if the family of my double first-cousins has been inbreeding for a very long time. a very, very long time. like for fifty generations or more. then the relatedness between all the family members, including these double first-cousins, will be even closer. natural selection ought, then, to favor such double first-cousins jumping in to save each other.

as wade and breden showed (see also previous post), inbreeding can help to accelerate the rate of the evolution (or frequency in a population) of altruism genes [pg. 846]:

[T]he increase in matings between homozygous parents decreases the genetic variance within families, because these matings produce genotypically homogeneous arrays of offspring.”

repeated inbreeding in a family reduces the diversity (whoa!) of the allele types within that family, and if we’re talking about “genes for altruism” here, then the variety of those must get reduced within inbred families, too. in a population that consists of, say, ten inbreeding families, the one that has super-duper altruism genes that lead all of its family members to help each other out more than the members of the other families will have the advantage (provided selection favors that advantage for whatever reasons). and those super-duper altruism genes will no doubt eventually spread to the other families since, in reality, no family groups inbreed 100% of the time anywhere — there will pretty definitely be gene flow between families. so then you’ll get a whole population of super-duper family altruists (note that these people are NOT altruistic to unrelated individuals).

the human populations on earth today that inbreed most closely (within patrilineages) and often practice double first-cousin marriage — AND have been doing this for prolly at least a couple of thousand years (time depth) — are the arabs (who later spread these mating practices to the maghreb, the mashriq and far off places like iraq and afghanistan and all the other ‘stans) and some peoples in the levant like the druze. i think that, because of their long-standing mating practices, they are the prime human examples of wade and breden’s accelerated evolution of altruism thanks to inbreeding.

previously: inbreeding and the evolution of altruistic behavior and more on inbreeding and the evolution of altruistic behavior

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double first-cousin marriage

’cause you can never have too much of a good thing, right? (~_^)

double first-cousins are just that — first-cousins twice over:

“‘Double first cousins’ arise when two siblings of one family reproduce with two siblings of another family. The resulting children are related to each other through both parents’ families. Double first cousins share both sets of grandparents in common and have double the degree of consanguinity of ordinary first cousins. Genetically, they are as related as half-siblings.”

double first-cousin (d1c) marriage looks (or can look) like this:

in the parts of the world where father’s brother’s daughter (fbd) marriage is practiced, d1c happens at not a small frequency. in afghanistan, for example, 6.9% of consanguineous marriages are to double-first cousins (46.2% of marriages are consanguineous).

d1c marriage obviously changes the degree of relatedness within the d1c family, compared to other cousin-mating families that is. broadly speaking, double-first cousins are like half-siblings in terms of genetic relatedness.

if you use my system for calculating new-and-improved coefficients of relationship/relatedness, which is based on the differential inheritance of the x- and y-chromosomes, then the relatedness of two brothers from a father’s brother’s daughter double first-cousin mating (fbd d1c mating) looks like this (if i’ve done the maths right!**):

B-B (FBD D1C marriage)
**a man and his FBD share 1/8 of their autosomal dna; a woman and her MZS share 1/8 of their autosomal dna + 1/4 of an x-chromosome + another 1/8 of an x-chromsome.
**therefore, two brothers from an FBD D1C marriage share: 1/2 autosome + 1/16 autosome + 1/16 autosome + 1/2 x-chromosome + 1/8 x-chromosome + 1/16 x-chromosome + y-chromos
ome
(96.42% x 0.5) + (96.42% x 0.0625) + (96.42% x 0.0625) + (2.60% x 0.5) + (2.60% x 0.125) + (2.60% x 0.0625) + 0.99% = 0.5701

so, an fbd d1c mating raises the genetic relatedness of two brothers to the same level as that of two brothers from an mzd marriage:

what would be interesting to know is if fbd d1c marriage was more prevelant in the past when transport wasn’t so good and people prolly didn’t marry over such long distances. in other words, there might’ve been more cousin marraige, including double first-cousin marriage, in general in the past.

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**have i got 1/16 autosomal dna too much there with the two brothers (B-B)?

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