Tuesday, February 21, 2012

Race and sex differences in infant digit ratios

This recent study examined 2D:4D digit ratios for 364 infants from birth through the second birthday. (Digit ratios are thought to reflect prenatal exposure and/or sensitivity to testosterone.) Six measures were taken: during the first month, the first and second birthdays, and both the left and right hands at each visit. I averaged the six measures for both boys and girls: Cohen's d for the difference between the boys'and girls' means is .167--a small difference.

The authors gave Cohen's d for the black-white differences for each of the six measures. I averaged them and got .383--a moderate difference with blacks being more masculinized. (The number might be an underestimate because they ignored the fathers and based racial classification on the mother's race alone. Mixed-race babies might have blurred the difference.) Anyway, in this study of prenatal testosterone, the size of the racial gap is more than double the gender gap.

8 comments:

clown said...

What's the explanation for this increased sexual dimorphism seen in blacks? Are African tribes more recently polygamous than European ancestors? If so, why? What's the evolutionary advantage? And do you have any data on Asians? My guess, just based on how they appear, is that Asians have the least sexual dimorphism of any ethnicity. To quote Lucille Bluth from Arrested Development on Asian girls vs boys: "You have to strip them down to next to nothing to tell the difference."

Anonymous said...

What's the explanation for this increased sexual dimorphism seen in blacks?



Does anybody on this site even know what "sexual dimorphism" means? I get the distinct impression that the answer is "no".

You cannot say anything about "sexual dimorphism in blacks" based on a comparison of finger sizes (or even of penis sizes) in black and white males.

Sexual dimorphism in blacks says nothing about differences between black males and white males, or between white females and black females.

If there were indeed increased sexual dimorphism in blacks compared to other races, this would manifest itself in the form of an exceptional degree of difference between black females and black males.


Not - and apparently I cannot emphasize this enough - between black males and white males.



If there is an unusual degree of sexual dimorphism in blacks compared to other races, we would expect that, on measuring the size and body mass of black males and black females, the difference between the sexes would be larger than in non-black races.

Sexual dimorphism is the difference between males and females of the same species, or in this case of the same race. For instance, in certain species of insect the female is significantly larger then the male. Among elephant seals, the adult male is about twice as large as the adult female.

Even if - hypothetically speaking - black males were three times larger than white males(!), this would tell us nothing about sexual dimorphism in blacks. Sexual dimorphism in blacks is entirely dependent on the differences between black males and black females, and has nothing to do with the differences between white males and black males.

Anonymous said...

As for the question of whether black males are more "masculine" than the males of other races, which is what is being mistakenly addressed here under the heading of sexual dimorphism, the answer seems to be "no". With the proviso that "masculine" is an ill-defined concept.

Aeoli Pera said...

'Does anybody on this site even know what "sexual dimorphism" means? I get the distinct impression that the answer is "no".'

This opener made my atheist detector go nuts :-).

Anonymous said...

The connection between atheism and sexual dimorphism being .... ?

Anonymous said...

Anyway, in this study of prenatal testosterone, the size of the racial gap is more than double the gender gap.


In general, the ethnic differences in 2D:4D are vastly greater than the male/female differences in 2D:4D within groups.

To put that another way, there is no such thing as a male 2D:4D ratio vs a female 2D:4D ratio. There is such a thing as an English male ratio vs an English female ratio, a Hungarian male ratio vs a Hungarian female ratio, etc.

Manning found a much greater difference in 2D:4D between Germans and Poles then between German men and German women, or between Polish men and Polish women. German women have a lower, "more masculine" ratio than do Polish men.

The truth is that 2D:4D looks like a vaguely interesting curiosity, but one which does not actually tell us much of importance.

Anonymous said...

A link to the Manning study which looked at 2D:4D in different populations. The graph in Fig.10 (page 178) sums it all up.

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