different mutation rates in different human populations

well this seems important! via race/history/evolution notes, an abstract from the society for molecular biology and evolution 2014 conference (in puerto rico! – teh scientists are always good to themselves whenever they can be (~_^) ):

Evidence for different mutation rates across human populations
Ron Do, David Reich
Department of Genetics, Harvard Medical School, Boston, USA

Although mutation rates (per base pair) have clearly changed across primate evolution, many analyses continue to assume that all present-day human populations have the same mutation rates. Recently, William Amos analyzed 1000 Genomes Project and Complete Genomics sequences and found evidence of significantly higher divergence rates on African than on non-African lineages since separation (W. Amos, PLoS One 4, e63048). The detected pattern was strongest in genomic regions of high polymorphism rate, a pattern that the author hypothesized was due to ‘heterozygote instability’, whereby gene conversion events surrounding heterozygous sites increase the mutation rate. To further test this observation, we measured the relative accumulation of mutations in lineages drawn from two different populations, using 25 deep genome sequences generated according to the same experimental protocol using the Illumina technology. We carried out pairwise comparisons of five sub-Saharan African (Dinka, Mandenka, Mbuti, San, Yoruba) and eight Non-African populations (Australian, Dai, French, Han, Karitiana, Mixe, Papuan, Sardinian) on all divergent sites. We observed statistically significant differences in the relative accumulation of mutations for many pairs of African and Non-African populations. Among the strongest differences is significantly more lineage-specific mutations in Mbuti than in Han Chinese (R=1.044, standard error (SE) =0.0015). On average, we observed about 1% more mutations on African lineages compared to Non-African lineages. We also observed some significant differences across non-African populations, with the Han Chinese who have experienced extreme expansions in population size associated with agriculture having more mutations than the Karitiana, a hunter-gatherer population from Amazonia who did not experience such expansions (R=1.015, SE=0.0014). The results are consistent across both European and African segments of the human reference sequence, so are not an artifact of reference sequence bias. Taken together, these results support the view that per-base pair mutation rates may be dynamically and substantially changing across humans.

cool!

wrt to greater number of mutations in african lineages: polygamy (and, therefore, older fathers)? life in the tropics?

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cousin marriage rates in modern china

surveys of late-twentieth century cousin marriage rates in urban china — places like beijing and shanghai — have found very modern marriage patterns, i.e. very low consanguinity rates (0.7% – 0.8% of all marriages between 1949-67 in those two cities being between first- and second-cousins).

rural areas, otoh, have remained more inbred — rural hubei province having rates between 2.8% – 4.3% between 1949-67.

zhaoxiong found that just the first-cousin marriage rate in lijiawan village in hubei between 1949-93 (note that cousin marriage in china has been technically illegal since 1980) was 8.4%. that’s quite a bit higher than the rates above, especially considering that it doesn’t include second-cousin marriages (the rates above do — who knows how many second-cousin marriages there were in lijiawan?).

zhaoxiong also found that mother’s brother’s daughter (mbd) marriage was the most common form, followed by mother’s sister’s daughter (mzd) and, then, father’s sister’s daughter (fzd). nobody married their father’s brother’s daughter (fbd).

as wang, et. al., point out: “[T]here is a long history of consanguineous marriage in China….” however, cousin marriage rates in china have been dropping since at least the middle of the twentieth century — but they’re still pretty high in rural communities.

the genetic ties are starting to loosen in china. if they keep it up, that could prove to be a good thing in terms of having a more cohesive rather than a clannish society. don’t ask me how many generations they’ll need to make this happen! wish i could be around in a few hundred years to see how it worked out for them. (^_^)

many thanks to m.g. for the zhaoxiong article! (^_^)

previously: cousin marriage in china and abridged history of cousin marriage in china and china today… and china and landlordism and what else happened during the middle ages?

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abridged history of cousin marriage in china

maybe it’s not even that. it’s more of a basic (edit: and tentative!) outline of the history of cousin marriage in china:

3rd century b.c.

– cross cousin marriage practiced: so that’s either father’s sister’s daughter marriage or mother’s brother’s daughter marriage.
bilateral cross cousin marriage: that’s two clans or lineages swapping brides back-and-forth [pgs. 629-30]:

“Granet also discusses cross-cousin marriage in ancient China…. Granet cites evidence to show that two clans would stand in a reciprocal relationship such that the members of one clan would always marry members of the other…. There were many clans which presumably, if Granet is correct, were arranged in pairs by this system. The women of the two clans would be particularly eager for its continuance, as it would bring their own kin into their husband’s clan….

“The evidence from terminology for cross-cousin marriage in ancient China is very complete.”

624-907 a.d.

– cousin marriage possibly banned during the tang dynasty (the tang code dates to 624 a.d.) [pg. 43]:

“The clause in the T’ang Code is sometimes expanded to include prohibition against cross-cousin marriage…. The clause seems to indicate only parents’ cross-cousins [so first-cousins once removed – hbd chick], not one’s own cross-cousins; if so, the interdiction is against inter-generation marriage rather than cross-cousin marriage. But the T’ung tien seems to show that during the T’ang period marriage with cross-cousins and mother’s sister’s daughter was actually prohibited.”

1364-1644 a.d.

– cousin marriage is prohibited in the ming code [pgs. 43-44]:

“Legal prohibition, however, came rather late, the first definite clause being found in the Ming Code. Since enforcement of this law proved rather difficult, in the Ch’ing [Qing] Code this interdiction was invalidated by another clause, immediately following it, which allowed such marriages.

“Footnote 41: G. Jamieson: Translations from the General Code of laws of the Chinese Empire, Chapter 18: ‘A man cannot marry the children of his aunt on the father’s side, or of his uncle or aunt on the mother’s side, because though of the same generation, they are within the fifth degree of mourning.” But a little later in the Li, it reads: ‘…In the interest of the people it is permitted to marry with the children of a paternal aunt or of a maternal uncle or aunt.'”

1644-1912 a.d.

– qing dynasty reverses cousin marriage ban (see above).

1980+

– cousin marriage prohibited in the Marriage Law of the People’s Republic of China.
_____

in the 3rd century b.c., according to the erya, the terms for cross-cousins (father’s sister’s daughter and mother’s brother’s daughter, i.e. the ones you could marry) were the same, and the terms for the other two types of cousins (father’s brother’s daughter and mother’s sister’s daughter) were distinct. at some point in time, i don’t know when, the terms shifted so that all the cousin types had the same name except the father’s brother’s daughter, i.e. the only one no one married [see feng]. a similar shift in cousin terminology occurred in germanic languages in the 1100-1200s. cousins used to be differentiated in germanic languages, but following (by a few hundred years) the ban on cousin marriage by the church, all cousins came to be referred to by just the one term.

so, at several points in chinese history, the emperors tried to put a stop to cousin marriage, but they never managed. the fact that there were laws against it means they thought, for whatever reasons, that it was a problem, so i’d guess that the practice was probably pretty common. common enough for the emperors to want to stop it anyway. you’re not supposed to marry your cousin in china nowadays — since 1980 — however, see this from an article published in 2001:

“Although the marriage rules that prevailed during the dynastic era of China’s history generally tolerated such marriages (Li 1950:99-100), they have been prohibited for genetic reasons in both mainland China and Taiwan since the 1980s (Tao, Wang, and Ge 1988:313; Liang 1995:14). In practice, however, this type of marriage continues in a great many villages (Wu, Yang, and Wang 1990:330).”

who knows what the frequencies of any of these cousin marriages were at any given time.

previously: cousin marriage in china

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cousin marriage in china

from “Rethinking cousin marriage in rural China”:

“This article considers cousin marriage rules among affines in rural Chinese culture, based on research in Hubei Province….

“Studies during the last several decades have proposed different explanations of cousin marriage among Chinese, but none provides an accurate and comprehensive principle to explain the rules that guide the selection of marriage partners among relatives in rural Chinese society….

“For the Chinese, qinqi (affines) are relationships created through marriage, and are sharply distinguished from members of one’s own lineage. In the kinship terminology, patrilateral parallel cousins are tang (FBS and FBD), but all patrilateral cross-cousins, matrilateral cross-cousins, and matrilateral parallel cousins are biao (remote) relatives for Ego, male or female.

“Marriage within the lineage, especially FBD marriage [father’s brother’s daughter marriage], is treated like marriage between kin and tantamount to sibling marriage. Because this type of marriage is strictly forbidden, both in custom and in law, it does not need attention here. (2) But marriages between other types of first cousins are regarded quite differently. FZD [father’s sister’s daughter marriage], MBD [mother’s brother’s daughter marriage], and MZD marriages [mother’s sister’s daughter marriage] for a male ego have usually been referred to as biao or zhong-biao (outside) marriages. Although the marriage rules that prevailed during the dynastic era of China’s history generally tolerated such marriages (Li 1950:99-100), they have been prohibited for genetic reasons in both mainland China and Taiwan since the 1980s (Tao, Wang, and Ge 1988:313; Liang 1995:14). In practice, however, this type of marriage continues in a great many villages (Wu, Yang, and Wang 1990:330).

Previous research indicates considerable regional variation in attitudes and preferences related to biao marriages. For example, in both Kaixiangong Village in Jiangsu Province, where Fei (1939) did fieldwork, and Phoenix Village in Guangdong Province, which Kulp (1925) studied, MBD marriage was preferred and FZD marriage frowned upon (Fei 1939:50-51; Kulp 1925:168). According to Hsu (1945:91), the people of West Town in Yunnan Province favored MBD marriage, tolerated MZD marriage, but disapproved of FZD marriage. On the basis of his fieldwork and that of Fei and Kulp, Hsu (1945:100) makes the generalization that MBD marriage is preferred all over China, whereas in most regions FZD marriage is not….

Controversy remains, however, as to whether among cousin marriages MBD marriage is preferred in every region of China. Freedman (1958:98-99), for example, contends that MBD marriage is not prevalent everywhere in China and certainly not in southeast China. Gallin (1963), based on his research in a Taiwanese village, considers that in China MZD marriage is not considered particularly problematic, and that MBD marriage is preferred over FZD marriage. Furthermore, MBD marriages are not favored so much as simply permitted, and FZD marriages tend to meet with disapproval more often than with tolerance. Gallin (1963:108) suggests that in some regions MBD marriages may be actively preferred, but in general they are merely considered acceptable.”

so historically — which is a loooong time in china — cousin marriage was very much a part of chinese marriage practices. but it sounds like the types and frequencies varied between regions — and prolly over time, too. china’s a big place, after all.

that’s why i questioned kirin, et. al.’s statement:

“This is not surprising because both of these groups [europeans and east asians] are mainly represented here by fairly large populations with no documented preference for consanguineous marriage.”

if they mean now — well, yessort-of. if they mean at all historically — and by that i mean anytime before the mid-twentieth century — then, no. that’s just not right.

i don’t have acess to the above article, but i’m gonna order it, so i’ll post more about chinese cousin marriage sometime soon(-ish). (^_^)

previously: china today… and what else happened during the middle ages? and china and landlordism and chinese kinship terms…

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