inbreeding in 18th and 19th century sweden

here’s a little more on inbreeding in sweden, again from this article: The Influence of Past Endogamy and Consanguinity on Genetic Disorders in Northern Sweden.

the researchers looked at parish record books to work out who married whom — and if and how they were related — in 18th and 19th century skellefteå which is right here:

the researchers assure us that, despite being a hair’s breadth away from the arctic cirle, skellefteå was not (is not!) a completely off piste locale and traded regularly with stockholm, etc., etc. so, skellefteå should not be a too a-typical example of mating patterns in sweden at the time. (still, like steve sailer pointed about about sweden in general, skellefteå is not exactly a cross-roads sorta place like istanbul or sicily. so, apart from the swedes and maybe some finns and a few sami and drunken mooses, it prolly wasn’t a very cosmopolitan place in the 18th and 19th centuries.)

how much inbreeding did they do? well, i’m glad you asked! [pg. 551]:

“Of the 14,639 marriage records examined, 3,043 (20.8%) were between couples related as sixth cousins or closer (F ≥ 0.00006), with a mean coefficient of inbreeding (α) for the total study population of 0.00204. First cousin unions comprised 2.05% of all marriages, and unions between couples who were second cousins and third cousins accounted for 2.24% and 2.91% of marriages, respectively.”

those are the averages of first-, second- and third-cousin marriages over the whole time period from 1720-1899. here are the percentages of first- through third-cousin marriages for each of the time periods looked at (click on chart for LARGER version):

as you can see, the rates increase up to the middle of the nineteenth century and then sorta drop off a bit in the last couple of decades. we’ve seen the increase in the eighteenth and nineteenth centuries before in italy and spain, and increasing cousin marriage rates was, apparently, the general pattern for much of europe in the nineteenth century:

“Prior to industrialization an inbreeding pattern characterized by increasing values throughout the 19th century was common to many societies, both European (Calderón et al. 1993; Morales 1992; Pettener 1985) and American (Gradie et al. 1991; Madrigal and Ware 1997). In many European populations, inbreeding was highest in the period from 1875 to 1915 (O’Brien et al. 1988)….” [source]

so, sweden was pretty typical for its times in this regard.

how do the swedish cousin-marriage rates compare to other european countries during the same period? well, for england, we’ve got a first-cousin marriage rate of 2.25% for rural areas in 1876. sweden’s first-cousin marriage rate for about the same time (1860-1879) was 2.66%, so pretty much in the same ballpark.

again, these rates come nowhere near the rates for early-twentieth century southern italy where the first-cousin marriage rate hit 56.97% in reggio calabria between 1910 and 1914. northern italy, on the other hand, is more like sweden (and england) in the nineteenth century with rates like 2.28% in rovigo between 1910 and 1914.

the other country for which i’ve got data from the same time period is spain. (remember that these numbers are probably not representative for the whole of spain. gredos is a mountainous area and remote, mountain populations tend to have higher than average inbreeding rates.) here are the percentages for first- through third-cousin marriages in gredos, spain, in the late-nineteenth and early-twentieth centuries:

only the two first periods here sorta overlap with the last two periods of the swedish data:

spain — sweden
1874-1884 = 17.30% — 1860-1879 = 11.42%
1885-1894 = 16.62% — 1880-1889 = 10.06%

so, gredos, spain, had quite a bit more first- through third-cousin marriages in these decades than sweden — but, again, gredos might not be representative for the whole of spain.

overall, then, the swedes did not have very high inbreeding rates in the eighteenth and nineteenth centuries. the cousin marriages rates for sweden during the period were comparable to those in england and probably also northern italy and perhaps even spain. remember, however, that the swedes do not have the same depth of outbreeding as other areas of northern europe. they may have had similar cousin marriage rates to other northern europeans in modern times, but they were likely marrying their cousins for longer during the early medieval period.

previously: inbreeding in sweden

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