Black and White


I ran into an interesting review of birth outcomes in biracial couples.  Relative risks (relative to white parents) went like this:

WB      BW       BB

1.2        1.75      2.08               (for low birth weight)

1.17      1.37      1.78                (for preterm birth)

1.42     1.51       1.85                (stillbirths)


Here, WB means a white mother and black father,  BW means a black mother and white father.  People have looked at the general pattern of higher birth risks in blacks for some time, without much success.  Differences in SES, income, education, and amount of prenatal care do not explain  it.   I wonder why the outcomes are worse in BW couples than WB couples.  Could be a hint.






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20 Responses to Black and White

  1. imprint says:


    Africa has traditionally had lower paternal investment and less monogamy. So you would get selection for epigenetic imprinting of male gametes to try to up-regulate resource consumption by offspring, using up the mother’s scarce resources before they can be spent on future children with different fathers. In response, adaptations in women would evolve to down-regulate offspring resource consumption. In Africa these effects should be in rough balance.

    With a black father and white mother, the child has up-regulated resource requirements, but suffers from background environmental and genetic problems. With a white father and black mother, the mother’s system downregulates provision to the developing offspring, but there is less countervailing pressure from the father’s sperm. So the offspring is more likely to suffer low birth weight or die in childbirth and suffer from other early maladies.

    This model predicts a sex difference, but it predicts that WB couples should have better outcomes than WW, and that BB should have better outcomes than BW. It gets closer to the data if we add some kind of non-sex-based B vs W difference, which is doubled for BB, but still doesn’t look like a great fit with the data.

    Alternative hypothesis:

    R vs K selection driven by disease plus reduced paternal investment have adapted B mothers to invest less in offspring in utero. Also doesn’t look fabulous with this data.

    What’s your theory? I’m stumped.

    • gcochran9 says:

      Magnified maternal-fetal conflict (as you suggest) along with greater genetic load in Africans might do it.

      • imprint says:

        James Flynn and Richard Nisbett have made much of some studies that found higher IQ in WB children than BW children as an effect that couldn’t be explained by their hereditarian opponents.

        For example, in the celebrated old Eyferth study, which reported a lower IQ gap than usual, all the kids were WB (male soldiers and female locals), and maternal-fetal conflict could have been one contributing factor.

        If your theory turns out to be true epigenetics may become less popular among progressive types. Are there any easy ways to test the hypothesis?

  2. The fourth doorman of the apocalypse says:

    Hmmm, what about WW, WA, AW, AA, …

  3. imprint says:

    WW=1 was stated above.

  4. Jorge says:

    Wht-{} = .25, Wht-8==D = .75
    Blk-{} = 1, Blk-8==D = 1

    Wht-{} + Wht-8==D = 1
    Wht-{} + Blk-8==D = 1.25
    Blk-{} + Wht-8==D = 1.75
    Blk-{} + Blk-8==D = 2

  5. anon says:

    There’s something similar in cattle. Bos Indicus dam has a negative effect on birth weight and Bos Indicus sire has a positive effect. Both genders of Bos Taurus have a neutral effect.

  6. albatross says:

    How do you untangle differences in WB and BW couples? There are more WB than BW couples, and they have notably different divorce rates, so it’s very likely there are other diffferences.

  7. Nador says:

    There is also a difference in veneral disease load between the two races. Maternal infections are probably more significant for birth defects, so that would mean a greater burden on BW than WB.

  8. The fourth doorman of the apocalypse says:

    In an environment where increased intelligence is of little use to reproductive success (ie, outside those areas indulging in complex and large-scale civilization) it would seem likely that mothers would be selected to resist investment, in utero and beyond, in more brain tissue. The payback for such lineages would be less risk of maternal death and more live and viable young, and thus, out reproducing other lineages not taking paths.

    There is possibly also conflicting goals here: robust male offspring able to undertake rigorous conflict with other males vs increasing brain tissue?

  9. Steve Sailer says:

    I read somewhere long ago that doctors had a rule of thumb that pregnancies among blacks were one week shorter than among whites.

    If true (and I don’t have a source so don’t get to carried away with my factoid), this might be related to width of pelvis. As you might have noticed watching the Olympics last summer, narrow pelvises seem to make for faster or more efficient runners, which would have selection advantages. But, narrow pelvises would likely have disadvantages when it comes to birthing babies, such as selecting for adaptations such as shorter gestations and smaller skulls.

    • The fourth doorman of the apocalypse says:

      Clearly you have not spent much time perusing the derrieres of Chinese females. However, they seem to have more rounded birth canals or something. My personal experience with one short Chinese female who gave birth to 8 & 9lb babies suggests that their narrower hips are not an impediment.

      Another thing that is interesting to do if you live in a diverse community is to compare African American children with Chinese children. The AA children have tiny heads on very well-formed bodies, while the Chinese children have enormous heads on dinky little bodies.

      I leave you to draw your own conclusions.

    • p32 says:

      ”Analysis of gestation length in an obstetric population of indigenous African women revealed a mean pregnancy duration of 274.8 days, which is similar to values recorded in women of African descent elsewhere, but about 1 week less than what generally has been reported in women of European ancestry and Japanese women.”

      ”The length of gestation varies from species to species.”

    • Flip says:

      My father was an OB/GYN and he said that blacks have shorter pregnancies.

  10. imprint says:

    ” Differences in SES, income, education, and amount of prenatal care do not explain it.”

    Lead, alcohol, mercury, disease, diet, etc affecting prenatal development?

  11. dearieme says:

    “In an environment where increased intelligence is of little use to reproductive success (ie, outside those areas indulging in complex and large-scale civilization) …”: is there evidence for that?

  12. Priceeqn says:

    Who were the authors of that review?

  13. AG says:

    X-linked clue.

  14. pablo brandt says:

    Black wombs don´t seem to work right.

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