Where did I come from?


Phylogenetic Relationships among Humans

Allan Wilson, with his colleagues Mark Stoneking and Rebecca Cann, produced an estimate of the phylogenetic relationships among the humans which indicated a recent common ancestry in Africa. This conclusion was startling and caused people to re-evaluate their understanding of human history. Reaction in the scientific community was mixed. Wilson's reaction to strong criticism was to repeat the study, with an improved methodology.

Conclusions
In summary, Wilson and colleagues concluded that the 147 people, from five different geographic regions, had mitochondrial DNA which they had inherited from a single female ancestor who lived in Africa about 200,000 years ago. They also concluded that each of the non-African regions had been colonized repeatedly. They concluded that the results were not compatible with the Multi-regional Hypothesis, but instead they supported the Recent African Origin Hypothesis, of the origin of modern humans. Significance
This study led to the startling realization that modern humans were much younger than previously thought. This meant that the development of language, culture, technology and other human attributes occurred relatively rapidly.

Suddenly people realised that there must have been multiple species of humans coexisting in the past. This naturally lead to speculation about their interactions. Did they fight one another? Did they mate? Did other species go extinct because of disease transmitted from the emerging human species? Were they outcompeted, and if so, how?

The idea that all modern humans had mitochondrial DNA whose ancestry could be traced back to a single woman in Africa led to the concept of a "Mitochondrial Eve", an allusion to the Judeo-Christian creation story. Much effort was needed to correct the misunderstandings which arose, to make plain that each part of our genomes can have its lineage traced back to some different individual in the distant past.

Reactions
There was a very strong and negative reaction to this study from many people. The primary criticisms were:

  • poor sampling
  • poor tree estimation
  • method of rooting tree susceptible to bias
  • inappropriate method for estimating genetic variation
  • weak statistical analysis
  • contradicted by fossil and morphological evidence

Response by Wilson
These hypotheses of human origin remained testable. If a more rigorous test were to give a similar result, then this first study, despite its weaknesses, was on the right track. Wilson responded to criticisms by initiating a new study. It used better sampling of African populations, a different method to estimate genetic divergences and improvements to the way in which evolutionary relationships were estimated.