The 'Out-of-Africa' hypothesis posits that modern humans derive from an African originator population, that spread outward replacing local populations approximately 100,000 years ago. In the May 11 Science, Ke et al. report the use of Y chromosome polymorphism analysis to test the origins of modern Asian man (Science 2001, 292:1151-1153). They looked at 12,127 men from 163 different populations across Southeast and Central Asia and typed three Y chromosome biallelic markers (YAP, M89 and M130). All of the samples carried at least one of the three African polymorphisms (YAP+, M89T or M130T). The absence of any ancient non-African Y chromosomes supports the hypothesis that Africans completely replaced earlier East Asian populations.