remember the woodley & bell paper about the connections between consanguineous matings and democracy (or lack of) that i said i was going to post a lot about? and then i got distracted? well, let’s get back to it.
by way of introducing woodley & bell’s idea that pathogens (and consanguinity) and democracy don’t go together, the last post in this thread of posts had to do with possible connections between pathogens and individualistic vs. collectivistic societies — i.e. seems like the more pathogens in your environment, the more collectivistic (ethnocentric, conforming, suspicious of outsiders) your society is going to be. now i want to look at one more paper before i get back to consangunity and democracy.
in On the Adaptive Origins and Maladaptive Consequences of Human Inbreeding: Parasite Prevalence, Immune Functioning, and Consanguineous Marriage [opens pdf], hoben, et al., present their finding of a correlation between frequencies of pathogens and frequencies consanguineous marriages in various societies around the world. it’s not a huge correlation — r = 0.39 — but it is there. the more pathogens you’ve got in your environment, the more likely you are to practice cousin marriage. kinda/sorta.
like the paper in the last post, these researchers worked from the consang.net data and the historic pathogen data from this paper. hoben, et al., didn’t include any nifty charts in their paper, and since i like my data served up visually, i made a chart of my own (click on image for LARGER view):
x-axis=their pathogen index. positive numbers (z-scores) indicate higher frequencies of pathogens; negative numbers, lower frequencies. bosnia-herzegovina has a z-score of 0; england has a z-score of -1.01. burkina faso has the highest z-score at 1.16. canada has the lowest z-score at -1.31.
y-axis=weighted mean consanguineous marriage rates.
i think there is a broad, general pattern here. and it makes some sense. as the authors say:
“[I]ncreased homozygosity and other genetic coadaptation that results from inbreeding can facilitate highly specific forms of immunological resistance to local parasites, and … these immunological benefits will be most pronounced under ecological circumstances in which endemic pathogens are more highly prevalent (Denic et al., 2008; Denic and Nicholls, 2007; Fincher and Thornhill, 2008a, b; Shields, 1982)…. [O]ur study indicates that, under certain circumstances (i.e., high pathogen prevalence), inbreeding may have advantages that outweigh its costs.”
but the correlation was not that high. and i think part of the reason for that is “technical” — that is that there are some “glitches” in the consang.net data that the researchers didn’t take into account.
take brazil, for instance. high on the pathogen index (0.930) but pretty low consanguinity-wise (4.348%). but that’s because brazil was fairly recently settled by westerners (and blacks and japanese) who brought roman catholic traditions with them when they settled there — in other words, cousin marriage prohibitions. so of course the consanguinity and pathogen frequencies don’t match very well for brazil. what should be looked at are native brazilian consanguinity rates which are more like 13% (only one study, unfortunately — see page 3** [opens pdf]).
the authors have also calculated the consanguinity data for slovakia as 11.618%, but that includes gypsies [pg. 10 – opens pdf] who are consanguineous wherever they go, so that is undoubtedly skewing the numbers for slovakia. the consanguinity figures for czechoslovakia are more like 0.2% [pg. 1 – opens pdf].
the BIG outliers, though, are the arabs and all their middle eastern/north african/south asian muslim buddies. they are the ones throwing off the correlation completely. i’m talking about most of the dots that are right in the middle of the chart: 0.5000 or lower on the pathogen index (so, not a lot of pathogens) but above the 20% consanguinity rate:
region – consang. rate – pathogen index
uae – 36% – -0.450
kuwait – 51.7% – -0.340
iran – 32.2% – -0.150
oman – 35.9% – -0.140
pakistan – 51% – 0.020
saudi arabia – 38.4% – 0.040
libya – 37.6% – 0.040
jordan – 31.2% – 0.160
afghanistan – 55.4% – 0.230
syria – 31.6% – 0.300
lebanon – 26.6% – 0.360
yemen – 35% – 0.410
egypt – 31% – 0.440
these societies are amongst those that have the highest consanguinity rates, and yet some of their pathogen index scores are very low. the united arab emirates, for instance, scores like france (-0.460) or the republic of ireland (-0.450). qatar has got the exact same score as australia (-0.250). and saudi arabia and pakistan have lower scores than italy (0.160).
clearly having pathogens in the environment is not the whole story when it comes to the push towards cousin marriage. and hoben, et al., don’t claim that either:
“To complement those partial explanations [economic, etc.] for the persistence of consanguineous marriages, in the present research we offer an additional explanation that we label the ‘parasite hypothesis of inbreeding.'”
a complementary explanation. i agree! prolly the most fundamental, underlying one i would guess.
(note: comments do not require an email. **note to english readers: sorry, no half-naked women on that page 3.)