A French Army Surgeon (1898/1972), a 30-year specialist in genitourinary diseases} makes reference to numerous anatomical distinctions which show a similar pattern of whites being between blacks and Orientals. .... We averaged the ethnographic data on erect penis and found the means to approximate:

Caucasians, 5.5 to 6 in. in length and 1.5 in. in diameter;

Orientals, 4 to 5.5 in. in length and 1.25 in. in diameter.

Although some call it a proof of black genetic superiority, another reason for the differences in penis and testicle size among the different populations could be that Asian women have simply been more faithful than their darker sisters in Africa. From what we have learned from chimpanzees and gorillas, the need for a large penis increases with a higher rate of female sexual promiscuousness. The more different types of sperm there are at one given time in the vagina, the more important it is for a man to have a long and thick penis to be sure he will be the father.

Testicle size: Although whites and blacks are very close in this regard, a white man's testicles are up to twice the size of testicles of men from the Far East.

"Although measurements of testis size by orchidometry in living subjects are difficult to standardize, they suggest smaller testes in Japanese and Korean men than in Caucasians. Weighing at autopsy is more accurate and showed that the size was twofold lower in two Chinese samples compared with a Danish sample. Differences in body size make only a slight contribution to these values." (Diamond, JM (1986) Variation in human testis size. Nature (London) 320: 488)

From http://www.penissizedebate.com/page48_penissize-race.htm#black