Introduction

Human genome diversity and recent human evolution are intimately related. The distribution of DNA sequence variation within and among human populations, however one chooses to define those populations, is the result of numerous evolutionary factors (migration, selection, mutation, and random genetic drift) operating throughout the history of our species and its recent ancestors. The emphasis of human diversity studies is shifting from simple description of which populations are ‘more closely related’ to identification of the evolutionary forces and historical events that are responsible for the extant diversity. The patterns of variation seen in mitochondrial, sex chromosome, and autosomal DNA are both the result of and reflect those factors, but differently.

Neither mitochondrial nor Y chromosome DNA is sufficient

Mitochondrial DNA (mtDNA) is relatively easy to study and has been exceedingly valuable in addressing a large number of evolutionary and taxonomic issues in a variety of species. However, it has many limitations and cannot provide information on many very relevant questions–especially those related to the amount of genomic diversity within and among human populations. Also, it can provide only partial information relevant to explaining the causes of the genetic diversity found among human populations. Two related characteristics of mtDNA are the primary reasons for the limitations: the absence of recombination and the maternal pattern of inheritance.