i know, i know — it’s easier to spot inbreeding (or outbreeding) from the presence (or absence) of a lot of long runs of homozygosity (roh) in the genomes of individuals in a population rather than short roh (see for example the central/south and west asians in this post, populations which everyone knows are regular inbreeders), but i haven’t got any data on long roh for separate, sub-populations (like italians vs. europeans), so we’re gonna have to make do with short roh (for now). and anyway, even the amount of short roh is reduced via outbreeding (and increased via inbreeding), so you can use it as a tool to try to work out a population’s mating history. it’s just not as easy/obvious as with longer roh.
so … the map below is taken from Genomic and geographic distribution of SNP-defined runs of homozygosity in Europeans.
the samples come from:
– the rotterdam study – the netherlands
– popgen – northern germany – specifically the schleswig-holstein region (in deutsch if you like)
– the monica augsburg surveys – southern germany – from the city of augsberg and two neighboring counties
– and popres, which, since this is a study of europeans, i presume must mean that the samples came from both the lolipop study in london and the colaus study, lausanne, switzerland — i discussed those two studies in this previous post (scroll down).
again, the problem with taking samples from people living in big cities is that, even if they may be natives of whatever country they happen to live in, they, or some of their recent ancestors, may have migrated to the city — so, who knows, for instance, if the samples from rotterdam tell us anything about rotterdam or even the region of the country in which rotterdam is located. probably tells us something about the dutch, but even then….
these researchers — nothnagel et al. — chose to look at roh that were 1Mb in length. that’s shorter than the 1.5Mb roh as delineated by the researchers who looked at the roh in russian populations. also, nothnagel et al. weighted the average roh in each population according to how much linkage disequilibrium was (estimated to be) present in each population. don’t ask! no, really — don’t ask, because i don’t really understand why they did this. here’s the wikipedia page for linkage disequilibrium. i know that you can have more ld in an inbreeding population and — you guessed it! — less in an outbreeding one. and, of course, other things like bottlenecks can affect how much ld is present in a population. nothnagel et al. found different amounts of ld in the populations in this study and compensated for that, but again i’m not exactly sure why.
anyway … here’s what they found. this map shows the subpopulation averages of the weighted number of roh per individual (the contour lines are guesstimates — educated guesstimates, but still guesstimates):
if you look closely, you’ll see that there’s a sort-of central band of a relatively low average number of roh (between 37-39) that runs from southern england down through beligum/the netherlands (rotterdam) and northeast france, southern germany and switzerland. and, as the researchers observed, and as we saw in the previous post on russia, the numbers of roh increase going northwards and decrease going south. until you get to southern spain and southern italy, southern greece, and (probably) a central spot in the balkans there, all regions where the average number of roh increases again. the researchers suggest that, perhaps, migration from northern africa to the iberian peninsula (that’s the only region for which they offer a possible explanation for this anomaly) explains the longer roh there — presumably they’re thinking of a bottleneck. maybe. but perhaps it’s due to greater historic inbreeding in southern spain — and southern italy and greece and the balkans. some data showing longer roh would help us tell one way or the other.
the researchers, btw, acknowledge that the areas indicated as having very low amounts of roh — colored in the lightest shades of yellow — i.e. northwest spain and eastern europe — are probably artifacts of the interpolation method that they used. also, for all you scots out there (you know who you are! (^_^) ), while i do predict that the average numbers of roh in scotland ought to be higher there than in england, note that there was no data for scotland included in this study, so the shades of the contours up there are wild guesses as well.
i’m quite surprised by the very low levels of roh in romania, but remember that one has to read this map with the underlying north-south differences in numbers of roh in mind, so perhaps the roh in romania really indicates an inbreeding/outbreeding rate in romania that is more like that found in, say, france/germany. dunno. in any event, it’s very interesting.
now i want to compare the average number of roh in eastern europe with western europe. that’s going to be kinda hard to do since 1) the two studies used different roh lengths (1Mb vs. 1.5Mb), and 2) the numbers from this study have been weighted. still, i think we can get at something of a (very!) rough picture by taking the numbers from germany as our starting point and using them to calibrate the results from the two studies. we can do this, i think, since the samples from germany came from the same sources in both studies — the popgen study for northern germany and the monica study for southern germany.
in the russian study, the samples from northern and southern germany were combined, so we only have one number for germany — which was lower than all the results from eastern europe, typically much lower (see map from previous post). the number of roh in the polish sample, for instance, was more than twice that found for the germans. the average number of roh in russia (Rus_HGDP) was also twice that of the germans. czechs, latvians, estonians — all higher than the germans.
now if we work westwards from germany using the results from the study in this post — the english, the dutch (rotterdam), and the swiss are all in the same range as the southern germans, while the southern french have an even lower average number of roh — and the irish (in dublin) and the czechs are in the same range as the northern germans. so all of these populations — and even the spanish and italians — have fewer roh on average than eastern europeans. which is what i would’ve guessed given what we know about the historic mating patterns of europeans beginning in the early medieval period (see mating patterns in europe series below ↓ in left-hand column).
maybe there’s another explanation for this difference between western and eastern europe — and for the apparent differences between central and southern europe. like i said above, a study or two looking at longer roh would help to clear up the picture one way or the other.
previously: russians, eastern europeans, runs of homozygosity (roh), and inbreeding and ibd and historic mating patterns in europe and ibd rates for europe and the hajnal line and runs of homozygosity and inbreeding (and outbreeding) and runs of homozygosity again
(note: comments do not require an email. ruh roh!)
chris pointed out a very interesting looking book (thanks, chris!), The Feud in Early Modern Germany by hillay zmora. i poked around the book a bit on google books and found that zmora is not afraid of sociobiology. chapter four of the book is titled The wages of success: Reproduction and the proliferation of conflicts. cool!
from a review of the book (thanks again, chris!):
“Feuds did not begin as disputes over honor; they were more often than not material disputes over resources, rights, and entitlements. However, once the dispute was under way, honor was then invoked and sustained the conflict. Feuding was shaped by the expectations of the moral community and so feuders explained and defended their actions to a public and were concerned to show that they were acting in the right.”
so it seems as though there may have been something of a shift in the motivations of feuders from the early medieval period in germany (bavaria) to later in the period (in franconia, the region zmora deals with). earlier in the period, feuds might be started solely over honor, although battling for resources was undoubtedly a — probably the — main cause of feuds. later in the period, feuds aren’t started over honor at all, although honor is often used as an excuse/rationalization afterwards. it’d be interesting to know whether or not this apparent shift was a real and general pattern across germany/europe over the course of the medieval period. further research is required. (~_^)
a second big shift in the nature of medieval feuding — and this one is a certainity — i found in another book by zmora, State and Nobility in Early Modern Germany: The Knightly Feud in Franconia, 1440-1567, in which we learn that, by this later point in the medieval period in germany (or franconia anyway), feuds were no longer being fought by kindreds like in the early part of the medieval period. they were now being fought by one nobleman and his followers (possibly some kin in there) versus another nobleman and his followers. that’s a big change [pg. 34]:
“On a descriptive level the feud was, fundamentally, a series of sporadic yet organised, usually small-scale raids invovling burning, looting, abductions, and causing all sorts of material damage. It was carried out not by kin groups, but by two principal feuders and their band of followers. The main victims were normally the rivals’ subjects. These violent attacks, however, were by and large restrained. They were regulated by accepted rules of conduct and by a more or less fixed repertoire of sanctioned methods, which in theory, and often in practice, precluded flagrant brutality. This was especially the case of feuds between noblemen. The fact that the Franconian noble families were closely interrelated militated against to-the-bitter-end feuds…. In most cases, feuds displayed a surprising degree of moderation. Unlike vendettas, killings were rare.”
and there’s a third change from earlier in the period! in the earlier feuds, people were often seriously wounded or killed — even though those feuding were also frequently related. here we see pinker’s (or eisner’s) decline in violence, i think.
more from the review:
“The mutual dependence on each other explains why they acted with relative restraint and violence was directed against property and tenants rather than noble neighbors, relatives, and acquaintances. For these reasons feuds involved careful deliberation, reason, and calculation; they were strategic enterprises in which one’s reputation was at stake. Zmora goes on to argue that feuding was also related to wealth and status. A reputation required defending and enhancing. For these reasons, feuders tended to come from wealthier lineages. Far from being ‘robber barons,’ they were more likely to be men seeking to indicate their wealth, personality, and fitness to rule — qualities that were more likely to attract a good marriage….
“He derives his inspiration not from anthropology or from the recent historical writing it inspired, but from sociobiology and evolutionary psychology. According to this interpretation, feuding was the consequence of male reproductive urges.“
that makes a lot of sense to me, although i would also guess that acquiring resources via these feuds motivated the feuders as much as showing off for the ladies (or the ladies’ families). having plenty of resources, of course, also ties into reproductive success — the more resources you have/control, the more wives/women/kids you can afford. some of the descriptions of the raids that were a part of these feuds involved cattle rustling — that’s just relieving your competitors of their resources while acquiring more for yourself. good deal (if you can get away with it).
in chapter four (i didn’t look through the rest of the book), zmora deals with the period from 1440 to 1570 in franconia and describes how 1) the wealthiest most successful families had the most kids and were more likely to survive as families over the course of the period (i.e. they didn’t disappear from the historical records like less successful families), and 2) the wealthiest, “Top Stratum” families were the ones who engaged in feuding the most. oh, and that tournaments became fashionable right around the height of the feuding (in the 1470s), he thinks because the franconians wanted to redirect the rambunctious behaviors of the young men from the rather destructive feuding to an activity that was (somewhat) less harmful to everyone involved — but in a way that they could still show off for the ladies. (~_^)
here are some excerpts from The Feud in Early Modern Germany [pgs. 78, 84-85, 91-94, 96, 98-100]:
“Between 1440 and 1570 Franconian nobles conducted 278 feuds. Plotting the incidence of feuding in Franconia over these years shows that violence was rising steeply from 1440 onwards until it peaked in the years 1460-79. The level of violence declined in the next two decades (1480-99), but then rose again to a second though lower peak in 1500-9. After this date feuding began to dwindle until it died out after 1570….
“The correlation between status and reproductive success has been confirmed for other regional or local nobilities in Germany of the same period. As Joachim Schneider has shown, the proportion of the elite families in Electoral Saxony rose from 16 per cent in 1445 to 27 per cent in 1527, whereas the proportion of individuals nobles from these families rose from 23 per cent to 36 per cent. Furthermore, examining the top six families, Schneider has found that the average number of persons in such families rose from 5.33 in 1454 to 9.83 in 1527/30 – a figure nearly four times higher than that of the other families in the elite of Electoral Saxony. Still, even this impressive figure was just about one half of the average of 17.5 persons in the six top families of the Wurzburg Lehenhof in 1495-1506 [i.e. in franconia]….
“It is now finally possible to draw some conclusions as to the families of those who feuded in the 1470s. Of the 37 Franconian families from which the feuders originated, 22 (59.5 per cent) were of high status, whether defined by princely service or by the possession of high-quality feudal property, or both. Given the close correlation between status and reproductive success, it can be assumed with a high degree of confidence that most of these 22 families had enjoyed — or rather suffered from — the demographic growth that was such a notable characteristic of this group in the second half of the fifteenth century…. Nobles from leading families were also the majority of those who feuded against princes in that decade (11 out of 16). In other words, the feuding scene in the 1470s was dominated by the large, wealthy, pre-eminent families.
“These families were victims of their own success, reproductive and otherwise. Their predicament was compounded by the fact that lordship-conferring fiefs, at the same time as they were becoming scarce relative to the number of progeny, were increasingly becoming the principal form of landholding. For between 1300 and 1500, and especially in the fifteenth century, Franconia underwent a process of feudalisation: fiefs proliferated because noblemen tended more and more to transform allodial property into fiefs to be then received from the princes…. As a result, the economic and social importance of fiefs, and in particular of lordship-conferring fiefs, cannot but have grown. Indeed, it has been demonstrated that feudal property was a factor of selection in the struggle of noble families for survival: families which had endured into the sixteenth century are conspicuously overrepresented in the Top Stratum of the Wurzburg Lehenhof; in fact, these families made up no less than 92 per cent of the Top Stratum in 1455-66 and 98 per cent in 1495-1519. The conclusion seems inevitable that the increase in the weight of fiefs in the property portfolio of elite families, coupled with the increase in the average number of males in such families, must have put a substantial strain on their resources. It seems hardly surprising that these families became entagled in numerous conflicts and that the spate of feuds in the 1470s was largely their doing….
“It may not be implausible to conjecture that the build-up of demographic pressure in elite families exacerbated competition not just over property but also over access to women. In one sense this is a tautology. These two types of competition are not as far apart as one might be tempted to believe. Aristotle Onassis is credited with the dictum that ‘if women didn’t exist, all the money in the world would have no meaning’….
“This is where feuds could come in. As a previous chapter has suggested, in a social environment shaped by relationships of inimical intimacy, feuds functioned, among other things, as cues designed not only to deter rivals but also to attract potential allies, including prospective marriage partners. As signals, feuds had the important advantage of being hard to fake: because they were costly — in the short run often conspicuously wasteful — undertakings, they provided clues as to the feuder’s economic situation; because they could not be carried out without the support of family, friends and followers, they advertised the extent and quality of the feuders’ social network; and because they involved real risks and at times demanded sheer physical courage, they conveyed information on the character of the man. In short, they exhibited traits that indicated wealth, personality and fitness all at once. Now it may be assumed that such signals grew all the more valuable as this social environment became crowded and as the precise landed resources that were critical for preserving ‘name and bloodline’ became ever scarcer. In these circumstances of heightened competition, feuds could be used to provide evidence of one’s ability to set up and maintain a household, or to provide one’s offspring with the means to do so.
“Contests over women as a major cause of violence between men is a universal human theme. It is a matter of nature, not of nuture. No society has managed to do without it, and for a good reason. The reward of success is huge: reproductive success. One of the most violent societies studied by anthroplogists provides a remarkable example: Yanomamo men who killed other men have more wives than their peaceful brethren. While such valorisation of aggression may be extreme, and indeed translates into an exceptionally high rate of fatalities, the basic attitude which underlies it is by no means confined to the Amazon rainforest. Sexual rivalries between men are also a major motive for homicide in monogamous Western societies. How far a link of this kind between violence and mating is true of feuding nobles in late medieval society is difficult to ascertain. A helpful intimation, however, is offered, yet again, by Wilwolt von Schaumberg. His biography touches on this issue in a crucial passage whose subject matter, tellingly, is feuds in Franconia:
“‘Since this war came to an end and Wilwolt von Schaumberg had nothing to do either for himself or for his relations, the time was one of minor raids. As such clashes seldom cease in the land of Franconia, some barons and nobles who were at loggerheads captured fortified places, burned down villages, and seized cattle … Wilwolt determinedly served his good companions who asked for [his help] in these affairs … and he made a big name (gross geschrai) for himself and earned recognition from the princes and the nobles….’
“The association here between violence and sex is explicit: feuding is not just about legal claims, nor just about earning the esteem of princes and fellow noblemen. It is also about impressing women, or rather impressing women’s fathers. In fact, Wilwolt’s biographer, the otherwise eminently sober Ludwig von Eyb, went further: the story of Wilwolt’s adventurous military life culminates in his wedding ceremony, described at the very end of the book. The hero has arrived. He has gained enough prestige and wealth to attract the daughter of one of the richest and most respected nobles in Franconia. The event is modelled on princely weddings, lavish and glamorous, with allegedly one thousand guests, some very prominent, and the indispensable paraphernalia of tourneying and dancing, where one could see ‘eighty-six elegant women and maidens’.
“Some supportive evidence for a possible link between feuding and mating indeed comes from tournaments, especially those of the Four Lands — Franconia, Bavaria, Swabia and the Rhineland. Initiated and organised by the nobles themselves, the tournaments of the Four Lands began in 1479, that is precisely at the end of that decade in which feuds between nobles reaches an unprecedented level. There are indeed some hints that these tournaments originated as a response to the rampant violence.”
(note: comments do not require an email. tournament.)
greying wanderer (thanks, grey!) pointed out to me (via) a very interesting study of russian/eastern european genetics which includes some runs of homozygosity (roh) data (which can provide clues of inbreeding/close matings among other things): A Genome-Wide Analysis of Populations from European Russia Reveals a New Pole of Genetic Diversity in Northern Europe. (dienekes has a really good explanation of roh here.)
in this latest study, khrunin et al. took a look at a handful of different ethnic russian sub-populations (from different locations in russia) as well as some other eastern european groups. most of the samples from russia they collected themselves — the rest came from other studies. here’s a list of which groups were included and where they came from:
– russians (n=384) from the archangelsk (mezen district, n = 96), vladimir (murom district, n = 96), kursk (kursk and oktyabrsky districts, n = 96), and tver (andreapol district, n = 96) regions
– veps (n=81) from the babaevo district of the vologodsky region
– komi (n=150) from the izhemski (izhemski komi, n = 79) and priluzski (priluzski komi, n = 71) districts of the komi republic.
all of these samples were collected by the authors — except for those from tver — and the researchers ensured that the subjects AND their parents were originally from whatever region in which they happened to find them (i like that!).
the data from other studies which they used are described in this paper and include:
– finns – samples from helsinki (n = 100) and kuusamo (n = 84) – kuusamo is really remote
– estonians (n = 100) – samples collected across the entire country
– latvians (n = 95) – samples collected in riga – parents had to be latvians
– poles (n = 48) – from the west-pomeranian region, so just on the border with germany
– czechs (n = 94) – from prague, moravia, and silesia
– germans (n = 100) – from schleswig-holstein in the north and the augsburg region in the south
– italians (n = 88) from tuscany – hapmap
– russians (n = 25) from the human genome diversity panel (hgdp) – i believe from the vologda oblast.
the data collected by khrunin et al. are really good, imho, since 1) they went to all the trouble of collecting samples from different regions of russia, and 2) the researchers tried to control for ethnic/regional origin. the quality of the data from all the other studies is kinda mixed, for my interests anyway. for instance, taking in samples in large, capital cities — meh — not so great. the residents of those cities could’ve come from all over the country. the northern versus southern sampling in germany is better; unfortunately, those data sets were combined together in this study (they’re kept separate in another really cool study which i will post about soon!). the estonian data set is interesting because the samples came from across the country. otoh, the polish data set is also interesting because it’s from such a specific region (and right on the border with germany).
ok. one last thing before i show you the results (i made a map!). different researchers define roh differently (*sigh*) — while there do seem to be some standards, there’s also quite a bit of variation, and different researchers choose to look for roh of varying lengths. in this study, the researchers looked for roh that were 1.5Mb in length (i’ve seen other researchers look for 1Mb in length). 1.5Mb is pretty short as far as roh go. if you recall, when a population has a lot of longer roh (like 4-8Mb or more), that’s a pretty good indicator of inbreeding. 1.5Mb — not so much. lots of short roh are a better indicator of something like a population bottleneck in the distant-ish past. but, what’s a girl to do? gotta work with what’s available, and if it’s short roh, so be it.
here (finally!) is the map. i took the data from this table. the map (first column of data) is of the average number of roh (of 1.5Mb) found in individuals in the different populations (nROH):
the most obvious thing to note is that the small, endogamous groups (the veps and the komi) have more roh than any of the other populations, except for the finns up in kuusamo (and i think that that’s probably due to a bottleneck — ethnic finns really only migrated to, and began to settle in, the area seriously in the 1600s, and i imagine it wasn’t very many of them — and being so far away from anybody else!). the veps and the komi are small populations and, historically, they didn’t marry out much (that’s why we have veps and komi people today), so they are somewhat inbred. definitely more so than the surrounding population.
another curious thing is the pretty high number of rohs in the baltic populations: latvians=0.58, estonians=0.61, and finns in helsinki=1.13. wow! what happened there? that’s something like three to five times the number of roh we see in italians (from tuscany) or germans.
the most interesting point for me, though, is that there is an east-west divide. it’s kinda vague, maybe, but i think it’s there: italians (tuscans) and germans at ca. 0.20, and then the czechs and poles right next door at 0.35 and 0.51 respectively. and everyone to the east, except the russians in kursk, higher again than those two figures. i think these results hint at what i’ve found in the history books on medieval europe, i.e. that western europeans began outbreeding earlier than eastern europeans and as a result wound up being more outbred. (see, for example, here and here — and the “mating patterns in europe series” below ↓ in left-hand column.)
finally, the authors of the study point out how it appears that the average number of roh in individuals in a population increases with latitude — and they mention that this has also been shown elsewhere (i’ll be posting on that paper — very soon!). if you look at the various ethnic russian populations, for instance, the russians down in kursk (Rus_Ku=0.28) and murom (Rus_Mu=0.39) have fewer roh than the russians further to the north in tver (Rus_Tv=0.49) and way up in mezen (Rus_Me=1.63!). however, the hgdp russian samples, apparently from the vologda oblast which is pretty far north, have relatively low numbers of roh (Rus_HGDP=0.44), so that doesn’t seem to fit. still, it does look like a real pattern to me. the authors suggest that this is due to the general pattern of how europe was settled (from the south to the north), as well as the fact that the farther north you go, the fewer people there are to mate with (so the more inbred you wind up being).
as i’ll show in my next post, though, while there does seem to be a north-south pattern to roh frequency in europe with more roh in populations to the north than the south, curiously the numbers seem to increase in southern europe as well (as compared to places in central europe like germany and france) — and strangely in the balkan region as well. i can’t imagine why! (^_^)
(note: comments do not require an email. kuusamo traffic jam!)
john derbyshire pointed out this new book to me (thanks, john!)…
…written by a fellow named mark weiner.
(clans are so IN nowadays! (~_^) )
here’s a little taste of what’s in the book — from the introduction [kindle locations 120-140]:
“What exactly is the rule of the clan? When I refer to the rule of the clan, I mean three related contemporary phenomena.
“First, and most prominently, I mean the legal structures and cultural values of societies organized primarily on the basis of kinship-societies in which extended family membership is vital for social and legal action and in which individuals have little choice but to maintain a strong clan identity. Today these societies include many in which the United States and its allies have a major strategic interest, such as Afghanistan, Yemen, Nigeria, and Somalia, but they have existed across history and throughout the world. Sometimes they are described as ‘tribal,’ though I tend to avoid the term because in English it carries a host of negative and racialist connotations. This strict form of the rule of the clan also includes the traditional Hindu caste system and Indian joint family, despite the manifest great differences between tribal societies and rapidly modernizing democratic India.
“Second, by the rule of the clan I mean the political arrangements of societies governed by what the Arab Human Development Report 2004 calls ‘clannism’….”
“clannism.” i like that.
“These societies possess the outward trappings of a modern state but are founded on informal patronage networks, especially those of kinship, and traditional ideals of patriarchal family authority. In nations pervaded by clannism, government is coopted for purely factional purposes and the state, conceived on the model of the patriarchal family, treats citizens not as autonomous actors but rather as troublesome dependents to be managed.
“Clannism is the historical echo of tribalism, existing even in the face of economic modernization. It often characterizes rentier societies struggling under the continuing legacy of colonial subordination, as in the Middle East and sub-Saharan Africa, where the nuclear family, with its revolutionary, individuating power, has yet to replace the extended lineage group as the principle framework for kinship or household organization. A form of clannism likewise pervades mainland China and other nations whose political development was influenced by Confucianism, with its ideal of a powerful state resting on a well-ordered family, and where personal connections are essential to economic exchange….”
“Third, and most broadly, by the rule of the clan I mean the antiliberal social and legal organizations that tend to grow in the absence of state authority or when the state is weak. These groups include petty criminal gangs, the Mafia, and international crime syndicates, which look a great deal like clans and in many respects act like them….”
and, of course, the mafia, and many other international crime syndicates (like balkan criminal gangs which have spread across europe during the past decade or so), ARE extended family-/clan-based. make no mistake — a lot of these groups are not just clan-like.
looks to be a very interesting book — and information packed! i look forward to reading it, and no doubt i’ll have more to say about it soon! (^_^)
(note: comments do not require an email. yemeni clansmen/tribesmen.)
i keep saying that i’ll define more clearly what i mean by “inbreeding” and “outbreeding,” but i never do. finally! — here i am, and i’m gonna do it! (^_^)
from the oxford dictionary of biology:
– outbreeding: “Mating between unrelated or distantly related individuals of a species.”
great. but what’s “closely related” or “unrelated” or “distantly related”? self-fertilization doesn’t really apply to humans (at least not very often — i hope), so where to draw the line between “closely related” and “distantly related”?
i’m primarily interested in the evolution of altruism and other “innate social aptitudes” in man [pdf] — and here’s where inclusive fitness comes into the picture, btw — and the role that inbreeding and outbreeding might play in all that.
inbreeding in and of itself does not change the frequencies of genes in a population — it just moves them around, concentrating them in certain lineages. however, wade and breden showed in some mathematical
wizardry modelling that, under certain circumstances, long-term, sustained inbreeding can, in fact, lead to increased frequencies of “genes for altruism” in a population.
wade and breden looked at four inbreeding scenarios: 1) self-fertilization (doesn’t happen in humans); 2) if the mating individuals shared half (50%) their genomes in common (like parent-offspring matings or sibling matings); 3) if the mating individuals shared 20% of their genes in common (this is somewhere in between first cousins and double-first cousins or uncle-niece/aunt-nephew); and 4) if the mating individuals shared no genes in common (not the typical pattern in human matings). most human populations do not practice parent-offspring/sibling matings — in fact, it’s usually avoided and considered by most as really icky. but quite a lot of peoples regularly marry first cousins, and some (in the arab world/middle east) even often marry double-first cousins — nor is the world short on uncle-niece pairings (southern india, for example — or hasidic jews).
wade and breden found that, under certain circumstances, long-term, sustained matings between individuals that share 20% of their genomes in common can lead in an increase in altruism genes in that population. first cousin marriage, probably the most common form of inbreeding in humans, is a little short of what wade and breden looked at, but it’s not terribly far away either (12.5% relatedness vs. 20% relatedness). you would think that the slope of the line for inbreeding at 12.5% relatedness would fall somewhere in between that for 0% and 20% (solid black line) on wade and breden’s lower graph here:
in clinical genetics, most researchers look at degrees of inbreeding that are between second cousins or closer, commonly referred to in the literature as consanguineous marriages. since i get a lot of my data on inbreeding from such studies, it’s kinda handy for me to define inbreeding as anything between second cousins or closer, but in reconsidering wade and breden’s results, i’m thinking that maybe i should only concentrate on first cousins or closer. for now i think i’ll stick to second cousins or closer, but i reserve the right to change my mind (it is a woman’s prerogative, isn’t it? still?).
so, on this blog:
– inbreeding = in a population, a general pattern of regular and sustained mating between individuals who are related to one another as second cousins or closer.
– outbreeding = in a population, a general pattern of regular and sustained mating in which individuals avoid second cousins or closer.
notice the “regular and sustained” bit. that’s important. we’re not talking here about occasional marriages between cousins. it has to be a regular practice in a society. i’m not sure what the frequency of the inbreeding needs to be. it will vary according to population size, of course — the smaller the population, the more closely related everyone’s going to be anyway (e.g. the yanomamo). in a larger population? — dunno. definitely when 50% of marriages are consanguineous over the long-term i think the frequencies of “genes for altruism” are going to increase pretty rapidly (i’ll come back to what sorts of altruism in another post). 30%? probably. 3%? not really.
outbreeding, too, needs to be “regular and sustained” to have any effect, i.e. to have a population slide back down wade and breden’s slope in reverse. one generation of outbreeding probably won’t have much of an effect, i think. evolution (natural selection) does take some time, after all. also, if one inbreeding group interbreeds with another inbreeding group, that’s NOT outbreeding according to my definiton. technically it is in biological circles, but if we’re talking about two populations that have been inbreeding for a long time and, therefore, have acquired a lot of genes for my “familial altruism,” then all they’re doing by interbreeding is swapping familial altruism genes. for example, if you’re the early medieval irish and are clannish because you’ve been inbreeding for who-knows-how-long, the “outbreeding” that you do with the vikings when they show up (probably) doesn’t count wrt altruism, because they’re a long-term inbreeding group, too.
to have any effect on the frequency of certain “genes for altruism,” outbreeding — like inbreeding — needs, i think, to be regular and sustained over the long-term, as it was with europeans (mostly northwest europeans) since the early medieval period (see also mating patterns in europe series in left-hand column below ↓ for more details) and, perhaps, some other groups like the semai in malaysia.
(note: comments do not require an email. hi there!)
as m. says:
“Reddit is a liberal hive and HBD-supportive comments get downvoted and buried. (basically anything that says that parenting/education/culture isn’t always that important and genes matter too). I thought it would be nice to maybe get a bunch of questions prepared to ask him, hopefully early on in the thread….
“anyway, people should create an account and ask away. to get in early, the celebrities usually start the thread a half hour earlier than the assigned time, so you can look at the newly created threads here and keep refreshing the page until it shows up.”
can’t say as i disagree with any of that. (^_^)
in addition, i would suggest that everybody avoid asking “hostile” questions. pinker is no (heh) blank slater — he’s practically an hbd’er. i think we should just pitch him some easy ones, so he can hit them right out of the park to the amazement of the crowds. make it a pleasant experience for all those lil’ redditors who might find hbd to be icky. (^_^)
so, put it in your calendars: tuesday, march 12 @6:00 p.m. et — steven pinker reddit ama. get there early to sign in or create an account for yourself if you don’t already have one.
(note: comments do not require an email. not my hat. not me, either.)