Bruce Lahn is the William B. Graham professor of Human Genetics at the University of Chicago. He is also the founder of the Center for Stem Cell Biology and Tissue Engineering at Sun Yat-sen University in Guangzhou, China. His previous research specialized in human genetics and evolutionary genetics, especially human sex chromosome evolution and the genetic basis that underlies the evolutionary expansion of the human brain. Lahn's current research interests include stem cell biology and epigenetics. His research on the microcephaly-associated gene, MCPH1, led to the hypothesis that an archaic Homo sapiens lineage such as the Neanderthals might have contributed to the recent development of the human brain. His research also suggested that newly arisen variants of two brain size genes, ASPM and MCPH1, might have been favored by positive natural selection in the recent human history. This research provoked controversy due to the finding that the positively selected variants of these genes had spread to higher frequencies in some parts of the world than in others.