The human species underwent a watershed change in the biochemical composition of its cell surfaces, via a genetic event estimated to have occurred ~2-3 mya, which is also the apparent period of the emergence of the genus Homo. In this talk, UC San Diego's Pascal Gagneux explains how this radical makeover of cell surfaces in early Homo would have brought about a mismatch between females lacking a certain cell surface sialic acid and males still expressing it, essentially providing a mechanism for reproductive isolation and speciation. Recorded on 02/05/2016. (#30641)