mating patterns in medieval norway

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

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

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


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

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

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

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

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

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

the arrival of christianity and cousin marriage bans, then, obviously occurred quite a bit later in norway than in the populations closer to the center of “core europe” — i.e. the franks (belgians and dutch) and the southeastern english — whose outbreeding projects were well underway by sometime in the 800s. the norwegians probably lagged behind in outbreeing by three or four hundred years, but, again, no idea exactly how much they’d been marrying their cousins beforehand. (similar case with the swedes.)

a couple of other notes from the article not directly related to norway:

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

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

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

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

where everybody’s fourth cousins

in response to the “people befriend their fourth cousins” study, smersh makes an excellent observation:

“You referenced some of this in your counter currents interview but this study makes things more clear.

Friends are as close to each other as fourth cousins.

Jews are also as close to each other as fourth or fifth cousins.

Therefore it is easy for Jews to make close friends by hanging out with other Jews.

Meanwhile, it is harder for gentiles to make close friends in mass societies, as people move around and no longer live in a village near a bunch of closely related people.

Certainly seems like it might explain a lot without implying a malicious intent on the part of certain parties.”

yes! maybe.

if it’s correct that people generally befriend their fourth cousins — and this is something that could vary between different populations (Further Research is RequiredTM) — then, perhaps, this could explain why places like iceland work so well, too. i don’t know what the average relatedness there is (does anybody know?), but presumably it’s something like fourth or fifth cousins as well. maybe then it IS really easy in such a place to have a — whatever — redistributive socialist system when it feels like almost anyone in your population could be your friend.


btw, that counter currents interview was, in fact, originally a hoover hog interview that somehow got syndicated over on cc. just want to give credit where credit is due. (^_^)

previously: friendship and natural selection (and human biodiversity)

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

random notes: 09/06/13

something that sobl1 asked me yesterday on twitter about the kurds led me to this on wikipedia:

“Barth finds in his study of southern Kurdistan that in tribal villages 57% of all marriages were cousin marriages (48% bint ‘amm marriages) while in a nontribal village made up of recent immigrant families only 17% were cousin marriages (13% bint ‘amm).”

the barth reference is: Barth F. (1954) Father’s brother’s daughter marriage in Kurdistan. South Western Journal of Anthropology 10, 164-171.

i haven’t seen it (yet), because it’s not online — only some tantilizing previews here and here — and, no, i still haven’t gone to the library.

what piques my interest here is the difference in cousin marriage rates between the traditional kurdish tribal villages (57%) and nontribal villages “made up of recent immigrant families (17%).

while it seems like it should be obvious that immigration would reduce cousin marriage rates, this is the first actual example i’ve (almost) seen of that. in other cases of immigration that i’ve seen — europe in general in the late-1800s (see second half of this post), germans in gdańsk in the 1500-1700s (see here), and, for example, not to be forgotten, pakistanis and their chain-migration patterns in places like the u.k. today — the cousin marriage rates have actually gone UP in connection with immigration. here — finally, then — is an example of cousin marriage decreasing with immigration — by a LOT, apparently.

so it seems like the effect of emigration on cousin marriage rates is something that can vary depending on circumstances, although what those circumstances are, is not clear to me.

Further Research is Required.TM (^_^)

a little bit on iceland (and the faroe islands) from The Faroe Islands: Interpretations of History [pg. 14]:

“The Church’s power [in the faroe islands] was also moral, and the workings of ecclesiastical law may have contributed to the relative impoverishment of freeholders. We do not know what ecclesiastical law was in the Faroes before the Reformation; only that in 1584 the Løgting complied with Frederick II’s request that a compilation of late thirteenth-century Icelandic law called the Stóridómur continue to be valid in the Faroes. Among other things, the Stóridómur set the bounds within which kinsmen were forbidden to marry; since marriage between cousins was held to be incestuous, lands divided by inheritance could not easily be recombined. After the Reformation, the Stóridómur was supplemented by secular laws prescribing harsh punishments for bearing or fathering children out of wedlock (death, if the parents were cousins) and allowing couples to marry only if they had a certain amount of land. Similar restrictions on marriage were in effect earlier as well. It could hardly be otherwise in so ecologically precarious a land, where overpopulation was always a threat. Thus the Seyðabræv had ‘established certain requirements for a man if he was to be able to marry and set up his own house’: none could do so without being able to support at least three cows. In effect, the poor were forbidden to marry.”

so it sounds as though by at least the 1580s — and very likely the late 1200s — cousin marriage was banned in iceland in this stóridómur (and, then, from at least the 1580s onwards on the faroe islands). that cousin marriage was banned in iceland starting in the late 1200s — if that’s what happened (i’m still not sure yet) — would fit my prediction that cousin marriage was probably banned there when the norwegian crown took over iceland in 1262. my bet is that the ban was introduced to the island at that point in time from the continent.

i haven’t found out much about this stóridómur — here is the icelandic wikipedia page google translated. sounds like it wasn’t compiled until the 1560s, but, perhaps, based upon earlier law tracts? dunno. it does mean something like “big judgement” or something like that.

and how about the faroe islands there?! those were some eugenical practices (if they enforced them, which it actually sounds like they did, if you read through the book above)! the faroese ought to be geniuses! (~_^)


conclusion: we need more physicists studying/being interested in human biodiversity/sociobiology/anthropolgy!:

(probable) reason: they’re more logical/have higher iqs.

examples: greg cochran, steve hsu, william shockley, and — i didn’t know — napoleon chagnon (h/t g-nice!):

“Darkness in Anthropology: A Conversation with Napoleon Chagnon”

“Iannone: How did your interest in anthropology begin? What made you want to be an anthropologist?

“Chagnon: My original major as an undergraduate in a local two-year college — Michigan College of Mining and Technology — was physics. At that time I had never heard of anthropology. I transferred to the University of Michigan after my first year and discovered that ‘physics’ was in the College of Literature, Science and the Arts and I would have to take courses in each of these fields. The only thing I could fit into my schedule for the social science requirement was a course in a field called anthropology.”


(note: comments do not require an email. the faroe islands!)

questions some of us thought to ask

joshua keating wrote on his foreign policy blog last week:

Questions you never thought to ask: Is inbreeding bad for democracy?

heh. (~_^)

well, some of us HAVE thought to ask that very question, a couple of people waaaay before i did — going back to 2002 in fact:

Consanguinity prevents Middle Eastern political development from parapundit.
Cousin Marriage Conundrum – from steve sailer. steve’s essay was also included in a volume co-edited by steven pinker, The Best American Science and Nature Writing 2004.

keating is referring to the woodley and bell paper, Consanguinity as a Major Predictor of Levels of Democracy: A Study of 70 Nations, which was published last year and which i blogged about here (and here and here and here) — and steve sailer also blogged about at the time.

just to refresh everyone’s memory, woodley and bell found a negative correlation (r = –0.632, p < 0.001) between the frequency of consanguineous marriages in the 70 nations at which they looked and the level of democracy in those countries. in other words, the greater the amount of consanguineous marriages in a country, the less democracy it probably has.

keating is not convinced:

“As a counterpoint, Iceland — a country so isolated and sparsely populated that people need an Android app to keep them from hooking up with a close relative — has had a representative parliament since the 10th century and a culture of individualism so strong they write Nobel Prize-winning novels about it. So there.”

two things.

first of all, it should be remembered that woodley and bell specifically looked for success at liberal democracy (fwiw, ymmv). from the paper:

“As conceived here, democracy refers to a system in which there is opportunity for competitive elections and deliberative referendums, with broad public participation encouraged for both (Vanhanen, 2003). Democracy in this instance refers exclusively to the liberal variety where the emphasis is on competitive politics, rather than the classical type in which the focus is on consensus building and statesmanship (Werlin, 2002). Two key characteristics of liberal democratic systems include the presence of institutions that permit citizens to express preferences for alternative policies and leaders, and the existence of institutionalized constraints that prevent the misuse of power by an executive elite (Inglehart, 2003; Lipset, 1959; Marshall & Jaggers, 2010).”

secondly, tenth century icelandic democracy was not an example of liberal democracy — and wasn’t right through to 1262 when the norwegian crown took over the governance of iceland. rather, the icelandic commonwealth was a system based on consensus which i posted about previously here.

early medieval icelanders were represented at their alþingi by regional chieftans known as goðar. nobody elected these goðar — they were the local strongmen from various areas of iceland, and they typically inherited their position, although these chieftainships were sometimes sold. you could, in theory, pick your own goði to whom you swore allegiance, but apparently in practice this rarely ever happened — because a lot of medieval icelanders were kin to their goðar [pdf], and it’s almost always bloody awkward to break it off with family — especially when you can’t easily move to the other side of the island or something.

so these early medieval icelandic “representatives” bore little resemblance to the representatives we have in modern, parliamentary systems (h*ck – maybe that was a good thing!). if you were an early medieval icelander, your alþingi representative was likely your kin, and you were probably stuck with him for life — until his son took over. this was not liberal democracy.

did the early medieval icelanders marry their cousins? i’m not sure. it’s very likely that their immediate ancestors from norway did (like the early medieval swedes probably did), and the medieval icelanders ignored many other of the church’s teachings and regulations on marriage at the time [pdf], so i wouldn’t be surprised if they did. the fact that medieval icelandic society seems to have devolved from one in which kinship was comparatively unimportant to a state where large clans controlled the place also suggests to me that they married their cousins — or at least mated awfully closely (they may not have had to marry very close cousins since they were such a small population to start off with).

having said all that, when trying to work out why the medieval icelanders — or any other group for that matter — didn’t/don’t have liberal democracy, it’s not really important whether or not they were marrying their cousins at the time in question. well, it is … and it isn’t. (don’t pull your hair out just yet.)

what is important (i think) is whether or not the medieval icelanders — or any group-X — had been marrying their cousins over the long-term. i don’t think that there’s an instantaneous connection between cousin marriage (or other close mating) and failing to manage a functional liberally democratic system. what i think that there is are longer term evolutionary processes connected to inbreeding/outbreeding patterns and the selection for individualism vs. familism or clannism. and if you have clannism, liberal democracy will just not work.

woodley and bell acquired their consanguinity data from here’s a map of those data:

consang net

what stands out right away is that consanguinity rates are very high in the arab world, the middle east, north africa, and places like pakistan and afghanistan, while rates are really low in the u.s. and scandinavia. that seems to fit the cousin-marriage-doesn’t-promote-democracy theory. but the cousin marriage rates in china are very low — same range as england and western europe. why don’t the chinese manage to have a liberal democracy then?

what you have to understand is that this map is a snapshot. it is a moment in time (mostly the twentieth century). it doesn’t tell us much about the history of cousin marriage in any of these societies — whether any of it’s been short-term or long-term — and without knowing that, we can’t even start to guess at any effects the mating patterns (and related family types) might’ve had on the evolution of behaviors in these populations, including those related to clannishness.

once you know, for instance, that up until very recently, the chinese actually preferred cousin marriage, then you can — i think — begin to understand why they’re clannish (or, at least, extended family-ish). and why, therefore, liberal democracy doesn’t work there — or didn’t arise there in the first place either.

rinse and repeat for all the other locales on the map.

see also Cousin Marriage and Democracy @marginal revolution.

previously: liberal democracy vs. consensus building and democracy and endogamous mating practices and “hard-won democracy”

(note: comments do not require an email. driving in iceland.)

random notes: 02/14/13

cousin marriage rates for german jews living in the prussian province of hohenzollern between ca. 1875-1920 (117 marriages):

– first cousin marriages = 16.2% ± 3.4%
– consanguineous marriage up to and including second cousins = 19.6% ± 3.7%

source [pdf]. original source: Reutlinger, W. 1922. Über die Häufigkeit der Verwandtenehen bei den Juden in Hohenzollern, und über Untersuchungen bei Deszendenten aus jüdischen Verwandtenehen. Arch. Rassenb. 14: 301-305.

a little more on these rates from In Search of Jewish Community: Jewish Identities in Germany and Austria 1918-1933 [pgs. 234 and 241]:

“On the other hand, there is considerable evidence to back up the impression that village Jews were marrying cousins and other close relatives in increasingly large numbers.[44] …

“[44] In Hohenzollern, there was an 11 percent rate of marriage to relatives (5 percent to first cousins) among Jewish couples who died before 1922; of those still alive in 1922, the rate had increased to 22 percent (16 percent to first cousins. These rates were several times as high as the rates for Christian marriages. See Wilhelm Reutlinger, ‘Uber die Haufligkeit der Verwandtenehen bei Juden in Hohenzollern und uber Untersuchungen bei Deszendenten aus judischen Verwandtenehene,’ Archiv fur Rassen- un Gesellschaftsbiologie 14 (1922): 301-303, quoted by Marion Kaplan The Making of the Jewish Middle Class: Women, Family, and Identity in Imperial Germany (New York, 1991), p. 273 note 206. See also Cahnman, ‘Village and Small-Town Jews,’ pp. 122-23, for an impressionistic discussion of the same phenomenon.”

so, the rates of consanguineous marriages increased for jews in hohenzollern over the period from 1875-1920. that pretty much mirrors the general trend of increasing cousin marriage rates right across europe at the time, only the actual rates for the hohenzollern jews were much higher than for most europeans — well, at least most germans.

this 11% consanguineous rate (5% to first cousins) for jewish couples who died before 1922 is a lot higher than the only other definite rate i have for european jews which is from alsace-lorraine in 1872-76 (so i’m thinking these might be kinda contemporaneous rates) — and that rate was 2.3% (consanguineous marriages).

see also: jewish mating patterns in nineteenth century russia.

a bizarre story on a case of cousin marriage and inbreeding depression from china that … well, i’ll just let you read it for yourselves. from A Family That Climbed Out of Inbreeding Depression [pg. 1064]:

“In 2008, a family was fortuitously found in Northeast China. Before the 1948 Revolution, this family was wealthy and owned vast amount of land. After nationalization, the family was given a tiny house with a small plot of land. Subsequently, during the Cultural Revolution (1966-1976), all landowning families in the country were severely prosecuted and socially ostracized. The social stigma on the members of former land owning families was so persuasive that any form of association with them was deemed as dangerous. At that time, there were two children of marriageable age. As their parents were unable to find unrelated mates from the society, they arranged an intra-family marriage between available first cousins. The union produced five offspring: three mentally retarded girls, one deaf-mute girl, and one mentally retarded boy who did not survive (Figure 1). The consanguineous (first cousin) parents supported their four disabled daughters throughout their childhood. By the time these daughters were of marriageable age, the Cultural Revolution in China was over and the social stigma of land-owning families was lifted. Thus, the consanguineous parents were able to arrange marriages of their four unfit daughters with four biologically unrelated men. The deaf and mute girl was married to a deaf and mute man from the same village. The three mentally retarded daughters were married to healthy men, of low socioeconomic status, and they resided in their husbands’ homes in the same village. The most severely retarded daughter was married to a poor man who came to their family looking for food; he was offered this daughter and accommodation within the family household. After marriages of their daughters, the consanguineous parents continued to support all four families, and each of the four daughters produced one healthy child (maximally allowed number of children in China at the time). The most severely retarded daughter accidentally lost one child at birth. Today, the consanguineous couple has four grandchildren who are attending regular school and are expected to marry to biologically unrelated mates….”

could the cultural revolution have encouraged cousin marriages during the time period in china? at least in some sectors? weird.

weregilds. did you know that weregild payments were made directly from one clan/kindred member to his corresponding clan/kindred member in the other clan/kindred (whichever was the aggrieved clan)? i didn’t.

i always imagined that all the weregild payments were sorta pooled together and passed from one clan to the other, but no … the father in one clan paid directly the father in the other clan, the father’s brother in one clan paid directly the father’s brother in the other clan, and so on and so forth. at least that’s how it was done in iceland … at least according to phillpotts [pg. 13]:

“Each class pays to the corresponding class of the opposite side, thus the father, son and brother of the slayer pay to the corresponding kinsmen of the slain. It is to be observed that the slayer pays nothing, the assumption being that he was exiled and his goods forfeited.”


i mentioned over here that edmund i (922–946) seems to have been one of the first anglo-saxon/english kings to have really tried to put an end to the traditional blood feuds in england (which were tied to the weregild payments — see above — if the weregild wasn’t paid when someone was slain, the aggrieved clan/kindred had the right to exact revenge on the slayer’s clan/kindred). re. one of his law codes (from phillpotts – pgs. 218-19):

Eadmund’s secular laws mark a notable advance in one respect: private warfare between families, as a result of a slaying, is to be stamped out, and the slayer alone is to bear the feud, if feud there is to be.

“II. 1. ‘If henceforth anyone kills any man, let him himself bear the feud, unless with the help of friends he pays full wergild within 12 months, whatever the birth (of the slain man,’ i.e. however high the wergild be).

“It must be remembered that a slayer is not involved in a feud unless he cannot or will not pay wergild; and if he can pay wergild there is no feud. So here we must assume that the slayer has not been able to produce the sum out of his own pocket, and that his kinsmen have been unable or unwilling to help him. That even this secondary liability of the kinsmen is purely voluntary is seen from the next clause:

“1. ‘If the *mægð* [kindred/extended family] forsakes him, and will not pay for him, then I will, that all the *mægð* be without feud, save the actual delinquent, if they give him thereafter neither food nor protection.

“2. ‘If however thereafter any one of his kinsmen shelter him, then let him be liable to the king for all that he possesses, and bear the feud with the *mægð* (of the slain), for they (the kinsmen) had before forsaken the slayer.

“3. ‘If however one of the other *mægð* takes vengeance on any other man than the actual delinquent, let him be outlaw to the king and to all his (the king’s) friends, and lose all that he possesses.'”

so edmund is the earliest example i know of in england of the state trying to position itself in between all of the homicidal lunatics in order to put an end to the violence. he (or the crown, i suppose) would pay the weregild if a clan/kindred wouldn’t in order to stop a blood feud from erupting.

edmund didn’t live very long though — he died (heh) in a fight when he was just 26 — so i don’t know how well-enforced his edict ever was.

(note: comments do not require an email. lotr weregild.)

“history as biology”

the best opening paragraph of a history book. ever!

from a book entitled Expansions: Competition and Conquest in Europe since the Bronze Age by an icelandic historian (or an icelandic fellow who trained as a historian, anyway), axel kristinsson [pg. 1]:

“1. History as Biology

“We are animals and the study of animals belongs to the realm of biology. I do not wish to sound extreme but the logic is inescapable. Our societies belong to the same general category as the societies of wolves or ants — groups of animals living together, interacting and depending on each other for their survival. Humans may very well be more interesting than either wolves or ants (at least to ourselves) and our societies are far more complex, which is why several scientific disciplines are dedicated to researching them. Nevertheless, they are *the same sort of things* as the societies of other animals, which is why we can expect some general principles of biology also to apply to humans and human society. In particular, human history should have some affinities to evolutionary biology. The evolution of human societies is the evolution of biological phenomena and the principles of evolution established by Charles Darwin might prove illuminating for human history as well.”

hear, hear!! (^_^)

unfortunately, he loses the thread pretty quickly [pg. 2]:

“Genetic evolution is an extremely slow process depending on random mutations and a reshuffling of genes to produce solutions that are beneficial to survival. These new genes then only become dominant over many generations as their benefits slowly assert themselves in the population. Significant changes often take millions of years.”

wrong. wrong, wrong, wrong.

still — the spirit is definitely right! (^_^)

(note: comments do not require an email. what icelandic people do for fun.)

low fertility rates ’cause we don’t marry our cousins

i was going to write a lengthy and very informative post about the likelihood that low fertility rates in our modern world might be related to the fact that we don’t marry our cousins very much anymore (and, in the west, haven’t been for quite a long time now), but there was a good write up in the economist a couple of years ago when that research from iceland (about the fecundity of cousins) came out, so i’m just going to quote that:

“Most explanations of the demographic transition are social…..

“Now yet another explanation has been added to the pot. This is that the mixing-up of people caused by the urbanisation which normally accompanies development is, itself, partly responsible. That is because it breaks up optimal mating patterns. The demographic transition is thus, in part, a pure accident….

“This suggestion is the corollary of a paper published in this week’s Science by Agnar Helgason and his colleagues at deCODE Genetics, a firm based in Reykjavik….

The study’s principal finding is that the most fecund marriages are between distant cousins. Using Iceland’s genealogical records, which allow the degree of relatedness between husband and wife to be calculated with great precision, Dr Helgason showed the optimum degree of outbreeding (measured in terms of the number of children and grandchildren produced) lay somewhere between cousins of the third and fourth degrees….

“The strong relationship between kinship and fertility was so unexpected that the researchers have not yet calculated exactly how much it contributes to the demographic transition. But even from the figures they present, it is clearly an important factor, and one that is likely to apply in other parts of the world where the records needed to prove it are not so good. Even in poor countries, birth rates are now falling fast. An important part of the explanation may simply be the additional choice of mates that development and urbanisation bring with them.”

(note: comments do not require an email. þú þarft ekki að lesa sögurnar heldur.)