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February 28, 2006

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Frank McGahon

Indeed, one of the participants in the BBC series, "Child of our time" is a blonde haired blue eyed girl whose mother is mixed race (black and white).

João da Costa

In Brazil and other societies where race-mixing is common such events are well known.
That shows that there is no "fundamental" genetic distance between the major races of man, in contradiction to what some people think (I mean, some people think that if you mix black and white it's "fundamentally" different than if you mix blonde and brunnete, for example. A brunette could give birth to a blonde child but a black female could not, so runs this way of thinking...).
Also, one could ask to people who think that races are essentially "extended families" how to bring "people-in-between" and phenomena like the one you brought here to their framework... because, as odd as it can appear, sometimes one black person can be directly a brother (sister) of a white person!

dsquared

It's also well known from those societies that the social and educational disadvantages of being black are correlated not to how many black ancestors you had, but to whether you have black skin yourself. I would actually bet decent money at decent odds that the little girl on the right hand side of that photograph will end up testing with an IQ that is greater than her sister's by a statistically significant amount. On objective, culturally neutral tests, natch, simply because white teachers will pay her more attention and have higher expectations of her.

Frank McGahon

Another thing is that cases such as these ought to give caution to those tempted to infer from "visible phenotype" all sorts of "essential" racial qualities. I'm particularly thinking of the "rational" bigots and "hbd" enthusiasts which is probably why this is causing such a fuss over at gnxp with most commentators there determined to conclude that either:

a) "bipaternal superfecundity" has occurred

b) the "white" sister will end up looking blacker when she gets older.

c) the whole thing is a hoax.

Abiola

Frank,

I'm reminded by what you and Dsquared have said of the following paper:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=140919

"Color and genomic ancestry in Brazilians"

["This work was undertaken to ascertain to what degree the physical appearance of a Brazilian individual was predictive of genomic African ancestry ... Our data suggest that in Brazil, at an individual level, color, as determined by physical evaluation, is a poor predictor of genomic African ancestry, estimated by molecular markers."]

Whatever the reasons for "whites" coming out on top in Brazilian society, hypothetical "superior" white genes for IQ and the like can't be among them ...

jonas

I have never seen such children. I doubt Michael Jackson's children are really his.

Matt

Hi, this is Matt, the Occidentalism guy. Both my parents have dark hair (mother brown, father nearly black), but my hair is blond. Apparently a throwback to my grandparents.

David B

In comments on GNXP I listed 4 possible reasons for the differences between these children:

1. Random Mendelian segregation

2. Multiple paternity

3. Partial albinism in one twin

4. Fraud.

I don't see that any of these explanations can be excluded by the information given in the original article. Simply going by inherent probabilities, (2) seems the best bet. As I pointed out, these are very young unmarried parents (the boy about 15 and the girl about 17 at the time of conception), and 17-year-old girls who sleep with 15-year-old boys probably aren't very choosy. I'm not being moralistic (I don't care what these kids do, except that my taxes are probably paying for them), just realistic.

gene berman

I once read an account (contemporary, during US slavery era) of someone who had travelled in the deep South (speaking specifically of Mississippi) remarking that there were many slaves he could not distinguish from white (or, indeed, from himself) except by their speech style. The same account mentioned the incidence of legal proceeedings wherein people visibly white were found to be black on the basis of one or another type of evidence of African ancestry (the "one drop"
rule) and subsequently, enslaved. It was also stated that many people, especially those resident in border states. were especially upset by the Dred Scott decision and the prospect that Southern escaped-slave bounty hunters operating in free states would become less choosey about whom they hauled back "home," recognizing the invalidity of skin color to determine who was black and who was not.

Abiola

"Simply going by inherent probabilities, (2) seems the best bet."

No, you mean "simply going by prejudices about teenage parents." Just because she slept with one 15 year old boy doesn't mean she'd sleep with you or anyone else who came along, and both children have a strong resemblance to each other, different hair and eye colors notwithstanding.

odocoileus

Invisible "blackness" has been an article of faith in US society for over a century. The fact that millions of white Americans have sub Saharan ancestry isn't something anyone wants to talk about.


Lots of discussion of this and other issues here: (beware the multiracial race cranks, who are just as much fun as the "white" variety)

http://backintyme.com/publishing.htm

Chuckles

[...wherein people visibly white...]

It would probably surprise some people that similar accounts were fairly well documented on West African coasts also. I once read an account of slaves taken from Igbo territory and the narrator was complaining that he couldnt distinguish the slaves from American mulattoes - and these were \"pure\" Africans, mind you. A freakish range of phenotypes exist among African peoples - and one does really need to appeal to miscegenation to explain it. Even if all the blondes in Europe died out; I am willing to bet that African populations could pretty well restock the worlds supply of blondes - given environment etc. As I type this, I recollect a West African girl I know, who would be \"white\" in the United States (but who in all likelihood has a mild (or extremely well managed) case of albinism.) Light and smooth skin with no splotches, blonde hair, and freaky eyes.

Jim

"The fact that millions of white Americans have sub Saharan ancestry isn't something anyone wants to talk about."

Quite true and the other side of that is the millions of black Americans who have European ancestry and strenuously deny it, or else just happen to be unaware of it. It has been out of fashion for the last few decades. This extends to a general ignorance in the whole country about the African origins of a lot of what is considered mainstream culture, and the European origins of a lot of African-American culture.

David B

Abiola: yeah, right, unmarried unemployed teenage mixed-race parents in Nottingham (drugs capital of the east Midlands) are no more likely than the general population to have multiple sexual partners.

But even in the general population the probability of multiple paternity would be of the order of 1 in 100, which is a good deal higher than the probability of all the 'white' alleles from two mixed race parents segregating out by chance. (I assume there are at least 10 loci involved in visible racial differences.) I'm not denying that the latter event can and does occasionally happen, but we shouldn't just *assume* that it is the correct explanation.

Andrew

Even if the babies had different fathers you'd still need all the alleles to segregate from at least one parent, as the mother is mixed race. And you'd have to add onto the prior probability of different fathers the additional condition that the different fathers be of different race (not unlikely, but p < 1). Once you add those onto the 1 in 100 chance of multiple paternity, it's not really more likely than the story as told...

Frank McGahon

[But even in the general population the probability of multiple paternity would be of the order of 1 in 100]

Where do you get that? On your own blog Razib links to a paper which "suggests" that 1 in 400 pairs might be bipaternal. I don't see any data on that and I'm sceptical even of that rate - for twins to be bipaternal you're going to have to see both impregnations take place close to simultaneously. Even in the "pulling a train" scenario, it's still more likely that the first guy in is going to be successful at impregnating the woman and the guy who's "stirring the porridge" is more likely to miss out.

In any case, I'd say the loci number less than 10. You might even get way with just two. Take a look at the couple in question. Seems to me that the principal "racial" markers here are skin colour and hair texture. Other secondary features (such as nose shape) wouldn't look out of place on someone conventionally identified as white.

David B

Frank: we don't actually know the number of relevant loci, but skin colour alone is usually estimated at around 5. Plus at least one each for hair colour, eye colour, and hair form. Then at least a few for facial features. I thought I was being very conservative in saying 'at least 10'!

"for twins to be bipaternal you're going to have to see both impregnations take place close to simultaneously"

- not necessarily. Since the eggs are not released simultaneously there could be up to a few days difference. (We are of course talking only about DZ, not MZ, twins.)

I said 'of the order of 1 in 100' because 'extra-pair paternity' in the UK at present is probably around 1 in 20, and I wanted to apply a generous 'discount' for the fact that they are twins. The useful phrase 'of the order of' covers everything to the nearest power of ten, so in this case it would include 1 in 400, though I suspect that in present UK circumstances this would be too low.

dsquared

[I said 'of the order of 1 in 100' because 'extra-pair paternity' in the UK at present is probably around 1 in 20, and I wanted to apply a generous 'discount' for the fact that they are twins]

If this was a "generous discount", then surely one in every five pairs of siblings would be twins, which is of the order of wrong.

David B

No, I meant, self-evidently, that of the order of 1 in 100 pairs of DZ twins would have different fathers. In other words, about 5 times less often than in the case of ordinary siblings. You may or may not think this is 'sufficiently generous', but your inference that "surely one in every five pairs of siblings would be twins" must rest on some misunderstanding.

dsquared

Oh, I see what you mean. However, since the gestation period for a human being is ten months, I would have thought that the minimum "discount" to apply here would be a factor of ten.

David B

I don't see what the gestation period has to do with it.

Suppose that at any given time the probability that a woman will conceive a child fathered by someone other than her usual partner is 1 in 20.

Suppose also that she has produced 2 eggs within a few days of each other (the precondition for DZ twins).

If both eggs are fertilised, there are 3 possibilities:

a) both eggs are fertilised by her usual partner

b) both eggs are fertilised by another partner

c) one egg is fertilised by her usual partner and the other by another partner.

Only case 3 will give twins with different fathers. The probability of case 3 depends on the gap between the two ovulations and the frequency with which the woman is having sex with both partners. E.g. if she has had a row with her usual partner and is only having sex with her other lover, case 2 is much more likely!

Frank McGahon

[not necessarily. Since the eggs are not released simultaneously there could be up to a few days difference. (We are of course talking only about DZ, not MZ, twins.)]

Well I assumed that we were talking about events of low probability and for the vast majority of DZ twins the eggs are released and implanted simultaneously.

[I said 'of the order of 1 in 100' because 'extra-pair paternity' in the UK at present is probably around 1 in 20, and I wanted to apply a generous 'discount' for the fact that they are twins. The useful phrase 'of the order of' covers everything to the nearest power of ten, so in this case it would include 1 in 400, though I suspect that in present UK circumstances this would be too low.]

But this is just the wrong way of looking at it. Promiscuity/infidelity is a necessary condition for bipaternal twins but it is by no means a sufficient condition. My point is that a bipaternal twin impregnation is a special case and can't usefully be compared to bipaternal non-twin siblings so the idea of applying a multiplier of five to it doesn't really get at how difficult/improbable such a case is.

Frank McGahon

[Suppose also that she has produced 2 eggs within a few days of each other (the precondition for DZ twins).]

I think you are conflating superfecundation (which is rare) and "ordinary" fraternal twinning. Once a fertilised egg has implanted, the woman stops ovulating. That is the general case which holds for the vast majority of ordinary fraternal twins. The special rare case is where the "stop ovulating" message doesn't get through and another egg is released. So it's probably not quite accurate to say that "2 eggs within a few days" is a "precondition" for dz twins. For the general case, "producing 2 eggs simultaneously" is the necessary condition.

David B

I wouldn't (and didn't) claim any great precision for my estimate, but I think you are clutching at straws to reduce the probability of superfecundation *as a proportion of all DZ twins*. In the situation where a woman is regularly having sex with 2 or more partners, the probability is not small. Your last point seems to overlook the fact that it takes between 3 and 7 days for eggs to get down the Fallopian tube and implant in the uterus - which actually means that if 2 eggs are released during the fertile period of the same cycle, they will *usually* both be available for fertilisation.

David B

...and I forgot to add that sperms can survive in the Fallopian tube for up to 5 days.

I can't find any reliable figure for the maximum period between the release of two eggs in the same cycle. One internet source says it would be 'within 24 hours', but I don't know the basis for this, and it may depend on the (incorrect) idea that ovulation occurs on a fixed day in the cycle. If only it were true the Catholic 'safe period' would be a lot safer!

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