Douglas Steinberg | Jul 23, 2000 | 8 min read
If humans are 99.9 percent genetically identical, as President Bill Clinton is fond of asserting when he extols the Human Genome Project, that 10th-of-a-percent difference has a lot of explaining to do. How does genetic variation determine a person's unique physical traits? Can it predict someone's susceptibility to a disease? Such questions, pertaining to the present or future, are what occupy most human geneticists. A small group, however, studies genetic variation as a clue to the past. Som