ABSTRACT
Why do we differ? It has been said that if a Martian were to visit the earth, humans would appear to be pretty much the same as one another. There would, of course, be some observable differences, such as sex differences, slight differences in coloration, clothing and, of course, language, but in the main these differences would be vastly outweighed by the similarities. In fact, if we are speaking about genetic diversity, then recent evidence suggests that humans are substantially less diverse than their close relatives, the great apes, including the chimpanzees (Kaessmann, Wiebe, Weiss & Pääbo 2001). This is surprising. Genetic diversity within a species usually increases over time as there are more opportunities for mutations to occur, given that our species’ lineage is
208 D A R W I N I A N D I F F E R E N C E S
the same age as both chimpanzee species (around 5-6 million years; see Chapter 1 ), humans and chimps should be approximately similarly diverse. One theory for the low diversity of humans is that a “bottleneck” occurred comparatively recently (30,000-130,000 years ago), and the human population dwindled to a small number of individuals. This had the effect of resetting the clock, and diversity has had only a comparatively short time to recover (see Premo & Hublin, 2009, for a discussion of relevant theories).
