when i was looking at the numbers for inbreeding in italy last night, i thought i noticed something curious — increases in consanguineous marriages in the years after the two world wars (edit: against a backdrop of a general decrease in inbreeding from 1910 through 1964).

i don’t think i’m imagining it (click on chart for LARGER version):

the chart illustrates the averages of the mean inbreeding coefficients over time (1910-1964) for all the regions in italy which cavalli-sforza, et. al., compiled church dispensation data (the data can be found here). i used data only from the regions which had complete data for all the years.

to me, it looks like there was an increase in consanguineous marriages in the time periods 1920-24 and 1945-49, i.e. post world wars. that’s not what i would’ve expected ’cause you’d think there’d be a shortage of men — including related men — after the wars, so you’d think close relative marriage would go down. yet, it seems like people went out of their way to marry relatives after the wars. maybe this is some sort of crisis response? circle the genetic wagons in (or immediately after) times of distress? i dunno.

(there’s a theory circulating out there these days that the reason that cousin marriage has increased — yes, increased — in arab countries during the past decade or two is because the population has increased so there are more cousins available to marry. if i can find the reference, i’ll share it with you. promise! (edit: see update at end of post.)

sicily is not included in the chart above ’cause, if you read yesterday’s post, you might remember that sicilians don’t have to get church dispensation to marry first-cousins-once-removed (1 1/2C) or second cousins (2C), so i didn’t want to include them with the rest of the italians and screw up the numbers. here’s what the chart for sicily looks like (click on chart for LARGER version) (edit: i updated the sicily chart so that it has the same scale as the italy chart.):

again, it looks like two post-war peaks (edit: and a great depression one?). there also seems to be a greater war-time dip during wwii for sicily. i think, tho, that there might be a more pronounced roller-coastery effect on the sicily chart since the sample number is lower (n=7 verus n=61 for the rest of italy).

it would’ve been interesting to have more data stretching further back in time for italy, ’cause on both the italy and sicily charts, the starting number seems a little lower than the wwi years. what was going on before 1910 in italy?

it would also be cool to have long-term data like this for other countries, including war-time periods. i’d like to know if this is a real phenomenon, or just a figure of my imagination.

oh. here are the numbers (click on the … oh, you know the drill!). italy minus sicily:


edit: boilerplate and boilerplate 2.0

previously: inbreeding in italy

update - articles regarding how rates of consanguineous marriages often increase alongside general population increases (or, more specifically, with greater survival rates):

The Prevalence and Correlates of Consanguineous Marriages in Yemen: Similarities and Constrasts with Other Arab Countries
Modernization and Consanguineous Marriage in Iran
The Role and Significance of Consanguinity as a Demographic Variable

another update: see also i wasn’t imagining it

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