There’s a book by a scientist named Rushton titled RACE, EVOLUTION, AND BEHAVIOR. Among other things he discusses penile differences between the races. The old “stereotype” that blacks are very well-endowed and Asians smaller endowed turns out to be true (as do most stereotypes!). We know this not only because large numbers of black, white, and asian penises have been measured and averages computed, but because condoms are manufactured with different sizes in different parts of the world. The condoms manufactured for black Africa are the largest, those for Europe and America in the middle, those for Asia (the Far East) the smallest. Condom manufacturers base the size of their product on research done on average penis sizes in a geographic area. Incidentally, penis size seems to relate inversely to intelligence. According to Rushton, blacks, who have the largest penises, have the lowest IQ, whereas Asians, with the smallest penises, have the highest IQ. This correlation does not apply to individuals within a group (I.e., a guy with a big penis does not necessarily have a low IQ), but they show up when we compare groups.
I can’t say 100% if any of this is true, as I have not done the research myself, I merely pass it along as a report on what Rushton has said.