Nicholas Wade, who is retiring from the New York Times, has an NYT article on recent evolution among African-Americans since arriving in the New World. The most obvious is for a decrease in the sickle cell gene variant, because the worst kind malaria is much less of a problem here, so the crude and dangerous sickle cell defense is overkill. 

There is tentative evidence for evolution of more defenses against influenza — in general, blacks had a hard time surviving in the North due to respiratory tract infections, which is one reason slavery faded out in the North, which something they ought to teach you when you study the Civil War. 

There is some arguable evidence for selection in a direction associated with a couple of particular African-American medical problems: hypertension and prostate cancer. Presumably, there were more than offsetting benefits. Prostate cancer correlates somewhat with higher levels of male hormones and hormone receptors, which (and this is a real stretch) might suggest that something (whether medical, climate, social, or cultural) in New World or North American environments was selecting for more masculinity among black men (or selecting for something else for which the cost was higher prostate cancer rates).

The chain of evidence for my surmise is extremely tenuous, but might go some way toward explaining a little bit about how some African-Americans wound up as global pop culture icons of masculinity.