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One for Rushton: Twinning in Africa
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Gebremedhin, Samson. 2015. “Multiple Births in Sub-Saharan Africa: Epidemiology, Postnatal Survival, and Growth Pattern.Twin Research and Human Genetics: The Official Journal of the International Society for Twin Studies 18 (1): 100–107.

The rate of multiple births in Sub-Saharan Africa is 1.7x that of European levels (h/t Emil Kirkegaard):

The multiple birth rate in SSA (17/1,000 births) appears to be higher compared to the level in other developing countries where the magnitude is unlikely to be affected by ART. A study reported that in many South and South-East Asian countries, including China, India, Indonesia, and Pakistan, the twinning rates remains below 10/1,000 births; likewise, the incidence in Latin American countries is similarly low (less than 9/1,000 births; Smits & Monden, 2011). The rate is also higher than the 1980s pre-ART multiple birth incidence in England and Wales (9.6/1,000 births) and several other West European countries (less than 10/1,000 births; Pison & D’Addato, 2006).

Multiple birth rates appear to vary substantially across the 25 countries included in the study. In general, the rate was higher in Central and West Africa countries and lower in Eastern and Southern Africa countries. The lowest (12/1,000 births) and highest (25/1,000 births) figures were reported in Ethiopia and Benin, respectively. The disparity can be likely due to genetic differences as variations in risk factors of multiple pregnancy (e.g., age and parity) across the countries are unlikely to be substantial.

One more piece of evidence for J. Philippe Rushton’s theory of a Negroid < Caucasoid < Mongoloid hierarchy in r/K life history strategies, as having bigger broods is more r-selected.

I noticed that twinning rates seem to be lower in the higher quality Sub-Saharan African countries, e.g. Kenya (highest on SACMEQ), Ethiopia (most impressive history/successful current development), Rwanda (Paul Kagame).

And Ethiopia being lowest here is perhaps not surprising, given them being evolutionarily closer to Eurasians than West Africans and historical admixture with Arabs.

Quick correlations between the twinning rate and other measures:

  • HDI: 0.07
  • IQ (Lynn 2012): 0.54
  • IQ (Lynn 2012, but including countries without data given as neighbors’ average): 0.44
  • SACMEQ (international standard test, like PISA): 0.61

Not rigorous by any means, but there’s probably something here.

***

Data table

Twins (/1,000) SACMEQ IQ IQ (proj) HDI 2018
Angola 15.7 71 0.581
Benin 25.1 71 0.515
Burkina Faso 19.7 70 0.423
Burundi 13.0 72 0.417
Cameroon 21.4 64 0.556
Comoros 20.5 77 0.503
Congo-Brazzaville 20.2 73 0.606
Ethiopia 11.7 68.5 0.463
Gabon 21.3 69 0.702
Guinea 22.3 66.5 0.459
Ivory Coast 23.9 71 0.492
Kenya 13.3 562 74.5 0.590
Lesotha 15.7 448 66.5 0.520
Liberia 19.5 68 0.435
Madagascar 14.0 82 0.519
Malawi 23.1 434 60.1 0.477
Mozambique 19.1 530 69.5 0.437
Niger 17.7 70 0.354
Nigeria 17.6 71.2 0.532
Rwanda 14.9 76 0.524
Sao Tome & Principe 21.7 67 0.589
Senegal 20.6 70.5 0.505
Tanzania 16.9 517 73 0.538
Uganda 16.4 506 71.7 0.516
Zimbabwe 13.5 72.1 0.535

 

 
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  1. Please keep off topic posts to the current Open Thread.

    If you are new to my work, start here.

  2. Before someone mentions the Benin Bronzes, thats present day Nigeria.

  3. songbird says:

    I’ll bet these twinning rates are really secondary to some other characteristic, like gestation time.

    • Replies: @The Big Red Scary
  4. @songbird

    This calls to mind the classic example of Sewall Wright concerning guinea pigs:

    “The average birth weight is smaller, the greater the size of the litter… this might be due either to a competition between the developing foetuses, or merely to an effect of a large litter in stimulating somewhat premature birth.”

    It was exactly to answer these kinds of questions that Sewall Wright introduced “path analysis”, a precursor to “causal inference”.

    Here’s Sewall Wright’s paper:

    https://www.gwern.net/docs/statistics/1934-wright.pdf

    • Thanks: songbird
  5. phdjkl says:

    As a Biology Teacher in Kenya in 1974, I found out that twins were considered very unlucky and were routinely killed upon birth. This may have accounted for the unusual absence of twins at our school.

    • Replies: @for-the-record
  6. @phdjkl

    This may have accounted for the unusual absence of twins at our school.

    In some African societies some neonates were killed because of beliefs in evil omens or because they were considered unlucky. Twins were usually put to death in Arebo; as well as by the Nama people of South West Africa; in the Lake Victoria Nyanza region; by the Tswana in Portuguese East Africa; in some parts of Igboland, Nigeria twins were sometimes abandoned in a forest at birth (as depicted in Things Fall Apart), oftentimes one twin was killed or hidden by midwives of wealthier mothers; and by the !Kung people of the Kalahari Desert.[8]:160–161 The Kikuyu, Kenya’s most populous ethnic group, practiced ritual killing of twins.

    https://en.wikipedia.org/wiki/Infanticide

  7. According to Chinua Achebe (Things Fall Apart) pre-Christian Igbos killed twins at birth (by exposure).

    And this custom may be making a comeback:

    https://www.nationalreview.com/corner/twin-killings-are-back-nancy-french/

  8. As I recall, there’s some town in Nigeria where the rate is 45%.

    …a little selective breeding could probably accentuate this trait.

  9. Where are Somalians on this?

    I don’t know how many Somalians live in Hungary, but one of them (a refugee) just raped a young woman on Monday.

    • Replies: @Anatoly Karlin
  10. @reiner Tor

    Impressive. How many Somalis are there in Hungary? 10? I tried to look it up, but I don’t know Hungarian, so can’t find any details.

    • Replies: @reiner Tor
  11. res says:

    Limiting yourself to Africa probably reduces the apparent correlations due to restriction of range (of all of the variables!). You might want to try adding in data for the non-African countries mentioned in your excerpt.

    https://fredrikdeboer.com/2017/07/24/restriction-of-range-what-it-is-and-why-it-matters/

    • Agree: Some Guy
  12. Of further prurient interest:

    Within the twinning cohorts, which groups have the highest multi-paternal rates.

  13. @Anatoly Karlin

    This is from 2018, and they say there were 40 of them at the time, and that they were a “close-knit community.” It’s a pro-refugees site, so they are quite sympathetic to them.

    https://www.unhcr.org/hu/4855-fotomodell-karrier-elott-all-a-szomaliai-menekult-lany-magyarorszagon.html

    Here’s another story, also from 2018, of a refugee girl, who fled to Hungary in order to escape the Somali patriarchy (and be able to study past age 15), and is now expecting a career in modeling. (Oh, the fabulous equality!) She doesn’t like Somali culture or Islam, or at least it doesn’t seem like that. She still wears a headscarf when talking to her mom back in Somalia, who “wouldn’t understand her new lifestyle.” Being a model means she will have lots of photos of her all over the internet, so I wonder if it will eventually be discovered by those back at home.

    https://www.unhcr.org/hu/4855-fotomodell-karrier-elott-all-a-szomaliai-menekult-lany-magyarorszagon.html

    • Thanks: Anatoly Karlin
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