I can’t write a better leading sentence than David already has: “In an article encouraging us not to use genetic tendencies for racist ends, William Saletan offers a possible genetic answer [to the question, Why are there so many black athletes?]”
One example is the RR variant of ACTN3, a gene that affects fast generation of muscular force and correlates with excellence at speed and power sports. The opposite variant of the gene is called XX. Tests indicate that the ratio of people with RR to people with XX is 1 to 1 among Asians, 2 to 1 among European whites, and more than 4 to 1 among African-Americans.