Infertilty Belt

Infertility Belt

It used to be the case (considerably less so today) that a significant fraction of women in central Africa, up to tens of percent in some areas, were infertile or subfertile, due to various STDs.  This seems to have been true for quite a while, up until the 1990s and back some indefinite amount of time, probably at least one or two centuries.  It might be older than that, but at this point nobody knows.  There was enough infertility that colonial administrators worried about keeping up the population, in the days before readily available antibiotics:  for example, the population of Gabon seems to have decreased between 1930 and 1950.

Most of this infertility was caused through  tubal scarring caused by gonorrhea and chlamydial infections.

If this pattern was around long enough, there could have been significant selection for resistance to the relevant pathogens, possibly generating high frequencies of alleles with odd or unpleasant side effects, as with  malaria and sickle-cell/thalassemia etc.  This would depend on the age of the behavior patterns that made this possible, on the antiquity of  the pathogens causing those STDs, etc.

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24 Responses to Infertilty Belt

  1. MawBTS says:

    I remember that you brought this up in another post. The above picture has no data for Nigeria, but this paper suggests 17% infertility for the 20- to 44-year-old cohort.

  2. Hokie says:

    Is selection the reason that chlamydia and gonorrhea end up asymptomatic a lot more than recent STIs such as syphilis? Did you find some genes that protect against them or their effects? Or do you think the selection was more psychological, and pushed in favor of shyness and chastity? Or is there no sign of any selection?

  3. dearieme says:

    Is it still the case that people think that syphilis (or a particularly form of it) was brought back from the New World by the early explorers?

  4. TWS says:

    Yikes that’s a lot of untreated STDs.

  5. Jacob says:

    The idea is that by causing infertility, the disease organism increases partner instability and therefore can get around more, right? I always thought that had interesting implications for social arrangements after the Pill.

  6. Sam says:

    With the DHS data sets ( available for many African countries, it would be interesting to see when this changed.

  7. bob sykes says:

    STD’s are very much more prevalent among African-Americans than among Whites. Are there any data on fertility impairment among African-Americans?

    STD’s seem to be more prevalent among the younger generations, too. Could that be affecting the observed below replacement fertility in most if not all White populations?

    • gcochran9 says:

      7 times higher for chlamydia, 15 times higher for gonorrhea, 6 times higher for syphilis, about 8 for HIV. If it was just one pathogen, you might wonder if there was a causative immunological difference, but it’s all of them, so behavior, at least mostly.

      STDs and their negative effects on fertility are more common in the general white population than they once were, but not enough to have much influence on current low birth rates.

  8. Yudi says:

    I’ve seen it argued that polygamy became much more common due to the Atlantic slave trade, since so many more men than women were shipped away. Is it likely that the infertility phenomenon would have existed before this change, and if so, why?

    • T says:

      You’ve seen it argued, but have you seen evidence? I really doubt that African polygamy rates changed at all, much less in a sustained way.

    • gcochran9 says:

      I don’t think we know whether the slave trade boosted the polygamy level. Polygamy is more common in most of sub-Saharan Africa than almost anywhere else. It’s more common in West Africa than East Africa, but there are lots of other differences – East Africa has a lot of Nilotics, pretty different from Bantu, while West Africa doesn’t.

      But then again maybe it was a cause. it would help if we had much info on what things were like before the Atlantic slave trade got going: off the top of my head I don’t know of much info of that kind.

      • Afrosapiens says:

        West Africa has no Bantus at all and has huge Nilotic groups like the Kanuri and the Songhai as well as Chadic groups like the Hausa. Nilotics and Chadics my have a combined population of 100 million in West Africa 1/4 to 1/3 of the total.

    • Sam says:

      I doubt the Atlantic slave trade made polygamy/polygyny more common in Africa for the following reasons:

      i)Polygyny is far more common among the Sahelian countries (somewhere between the 12th and the 20th degree latitude) than among the coastal West African countries (gulf of Guinea). Note that Senegal and The Gambia would fall under Sahelian rather than Coastal mainly for agro-ecological reasons.

      ii)Oral histories from many West African countries (e.g. among the Mandinkas) from 13th to 14 centuries (height of the Mali empire) suggest that polgyny is quite prevalent. If you had said slavery in general (including trans-saharan slave trade), that would somewhat weaken this particular point.

      (iii)Your claim rests on the premise that polygyny needs sex imbalance to start or increase significantly. Current empirical evidence shows that West African countries, where polygyny is very common (as high as 40-50% of marriages), show no sex imbalance. Given that there is no apparent sex balance, how does polygyny persist? Several reasons (lots of research papers on this): (a) high average age gap between polygynous men and their wives; (b)high re-marriage rate among divorced women (there are rarely unmarried women in these parts of West African countries); (c)high difference in age at first marriage between young men and young women (though not as high as (a)); (d)ease of divorce for men; (e)the presence of bride-price as opposed to dowry (this seems more of a correlate than a cause). Given these factors (I believe points (a) and (b) are the most important), polygyny persists in the African polygamy belt (Sahelian region) even though the region has no skewed sex ratio.

      • epoch2013 says:

        “Current empirical evidence shows that West African countries, where polygyny is very common (as high as 40-50% of marriages), show no sex imbalance.”

        The African slave traders that sold slaves to the Arabs and Europeans had a good supply of young men due to the existence of polygamy though. The argument could be turned around that polygamy was part of the cause for the large supply of African slaves.

  9. Dale says:

    I’ve seen apparently scholarly references to STD-induced infertility being a general problem when Europeans moved into areas of previously-isolated indigenous populations. The overview seemed to be that urban Europeans had developed a particularly virulent set of STDs and a partial immunity to them, along with relatively strict sexual norms that provided some protection from them. So this phenomenon may be much more widespread.

  10. Back when Harpending put out his tongue in cheek post on cads and dads I facetiously proposed that what we needed to limit the cads from taking over the earth via outproducing the dads was the purposeful engineering of the perfect STD which had 1) no other symptom but making a sex partner infertile 2) was very infectious and 3) was close to incurable.

    I was kidding at the time. But this post makes me now wonder if maybe the projected nightmare of the African continent overpopulating to a worst case scenario shall in part be handled by mother natures bag of tricks directed at this very strategy.

    Humanity is an outbreak. Mother nature handles species outbreaks by predictable strategies. Of course this is just idle speculation but look at our very recent past in brand spanking new venereal disease. We fucked our way into this mess of 7 plus billion humans maybe we will fuck our way out of it as well.

  11. Erik Sieven says:

    When 20% childless women correspond to a TFR of 5.3 the fertile women really had a lot of children.

  12. Afrosapiens says:

    Global epidemiology of infertility.

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