More on the black-white difference in sexual dimorphism

Reader Fenris suggests that if I am interested in black-white differences in sexual dimorphism, I shouldn't look at indirect measure like life expectancy, but should investigate height differences. I thought I had done it previously, but turns out that it was blacks and Asians that I compared before.

To make the best comparison, it makes sense to look at populations with environments that are as equal as possible. How about young blacks and whites measured recently? In fact, the data indicate that racial differences have reversed in the U.S. over time. I used Fenris' source and also found a newer one.

Here is the black sex difference in height minus the white sex difference for different age groups and periods:

Ages 40-59 (1988-94) -1.4 cm
Ages 20-39 (1988-94) -.2 cm
Ages 20-39 (2003-06) +.7 cm

As conditions have improved for blacks, their sexual height difference has changed from being smaller than that of whites to becoming larger.

Are blacks more sexually dimorphic than whites?

We know that some species are more sexually dimorphic than others. Species with big differences are polygamous and are called "tournament" species (due to the intense male-male competition) while those with small sex differences are monogamous and are called "pair-bonding" species. (Small) differences might exist across human races as well.

One indication of the degree of dimorphism is the gender difference in life expectancy. According to the NCHS, current life expectancy is 80.6 years for (non-Hispanic) white females and 75.8 years for white males. So among whites, women live 4.8 years or 6.3 percent longer. Expectancies among (non-Hispanic) blacks are 76.5 for women and 69.6 for men. So black women live 6.9 years or 9.9 percent longer. I take this as evidence that blacks are more sexually dimorphic than whites. (Keep in mind that racial differences are reduced since American blacks have roughly 20 percent European ancestry.)