Replacement Hypothesis

Allan Wilson’s laboratory at the University of California, Berkeley, was one of the first researchers to support the replacement hypothesis based on mitochondrial DNA.  He used the mitochondrial DNA to determine the rate of sequence evolution within the human species by the divergence between humans and chimpanzees.  According to their estimates, a single ancestral gene copy occurred between 166 000 and 249 000 years ago.

 The Berkeley group brought forth a gene tree which  implied that the ancestral sequence came from an African population.  It is from this study that the idea of the maternally inherited gene ‘mitochondrial Eve’ came.  This idea was misinterpreted by the popular press to mean that the entire human species came from a single woman frozen in time.

 These early studies have been the subject of much criticism.  However, later studies of both mitochondrial DNA and nuclear sequences have yielded similar conclusions.  These studies have found that gene genealogies are rooted among African DNA sequences.  There exists, reportedly, a greater sequence variation among Africans than non-Africans.  Levels of divergence among copies from populations throughout the world are low enough that it is believed that a common ancestor existed maybe as recently as 156 000 years ago.

 Other DNA studies pertaining to the beta-hemoglobin gene support the replacement hypothesis.  The conclusions attest the idea that archaic sapiens in Asia were bot isolated reproductively, but contributed to the ancestry of today’s human populations.