inbreeding in spain in the 19th & 20th centuries

over the last who knows how many posts, i’ve been looking at inbreeding (or mating patterns) in europe’s periphery. i started with ireland and moved around in a counter-clockwise direction to spain, italy and then greece. i posted about mating patterns in medieval ireland and spain (’cause this whole ball-game started with mating patterns amongst the pre- and post-christian germans) — and then when i didn’t have similar info for italy and greece, i posted some stuff about more recent mating patterns in those two countries. (if you’re wondering why i’m bothering with any of this at all, see this post.)

now i wanna backtrack for a sec ’cause i’ve got some data on inbreeding in spain in the 19th and 20th centuries (just like the title says!) — and some other interesting tidbits on mating patterns in europe in general. so, without further ado…

Inbreeding in Gredos Mountain Range (Spain): Contribution of Multiple Consanguinity and Intervalley Variation

first of all, the gredos mountain range is right here:

so, we’re talking about central spain here — not all that far away from madrid by the looks of it. however — and this is an important however — we’re talking about mountain populations here and mountain populations tend to inbreed more than low-landers since they’re often quite isolated.

and here we have (bottom line) the percentage of consanguineous marriages in the gredos mountains in spain from 1874-1975. the middle line is the inbreeding coefficient calculated to include all consanguineous marriages up to second-cousins; the top line, including all consanguineous marriages up to third cousins:

the peak of consanguineous marriages up to second-cousins was in the 1925–1934 period when the cousin-marriage rate hit 7.35% of all marriages. the lowest point was in 1965–1975 with a rate of 1.13%. the rate for the first decade recorded here, 1874-1884, was 3.44%.

what i think is striking is the similarity of this graph — especially the middle trend line — with this graph on consangunity in italy:

a gradual but steady increase for 50 years (100+ years in italy) with a peak in the 1920s and a sharp decline from then on. quite remarkable. this part of spain doesn’t show the post-wwii bump that italy did, tho. and spain was neutral in wwi, so never mind.

what’s going on? i’m not sure, but apparently italy and spain are not isolated cases re. this pattern:

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), while in Spain high inbreeding levels persisted for a longer time. In comparison with other large Spanish regions for which consanguinity has been studied, Gredos shows a general delay. Inbreeding increased during the first part of the 20th century, high levels of consanguinity persisted nearly up to the middle of the century, and a decrease in inbreeding was not noticeable before 1945. This pattern closely resembles that of another Castilian region, Sigüenza-Guadalajara Archbishopric (Morales 1992). However, it contrasts with that found in the north of Spain by Varela et al. (1997) in the Archbishopric of Santiago de Compostela, where inbreeding was at its highest between 1910 and 1920, with the inflexion point corresponding to 1920, and by Calderón et al. (1993) in Alava province, where the maximum level occurred between 1881 and 1901.

“According to Bittles et al. (1991), industrialization, greater population movement, decline in family size, and higher literacy rates would result in reducing the frequency of certain types of consanguineous marriages.”

yeah. but why the increasing rates in the 19th century? what was THAT all about? was it simply a result of increasing population sizes? maybe.

and, how did — if it did at all — this pan-european (and latin-american) increase in inbreeding affect the sentiments in the populations? could it have made them more nationalistic? sure, inbreed too much and you just get tribalism — but inbreed to just the right degree and, i think, you may get some strong nationalistic tendencies.

i dunno. haven’t thought it all through yet, and not gonna right now ’cause i’m already late for happy hour….

edit: boilerplate and boilerplate 2.0

previously: recap and whatever happened to european tribes? and inbreeding in europe’s periphery and il risorgimento and italian inbreeding? and ελλάδα

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