Until very recently, mitochondria were thought to be clonally inherited thr
ough the maternal line in most higher animals. However, three papers publis
hed in 2000 claimed population-genetic evidence of recombination in human m
itochondrial DNA. Here I review the current state of the debate. I review t
he evidence for the two main pathways by which recombination might occur: t
hrough paternal leakage and via a mitochondrial DNA sequence in the nuclear
genome. There is no strong evidence for either pathway, although paternal
leakage seems a definite possibility. However, the population-genetic evide
nce, although not conclusive, is strongly suggestive of recombination in mi
tochondrial DNA. The implications of non-clonality for our understanding of
human and mitochondrial evolution are discussed.