We have identified a nuclear pseudogene (numt) of cytochrome b (cytb) in chamois. The comparison of a fragment of 402 nucleotides of cytb and the pseudogene between the 2 species Rupicapra rupicapra and Rupicapra pyrenaica allowed direct measurement of relative rates and patterns of evolution. Mitochondrial genes evolved 7 to 12 times faster than their nuclear counterparts. Substitutions in the nucleus include a frameshift and a stop codon. Phylogenetic analysis of nuclear and mitochondrial lineages on Rupicapra and related species showed that the nuclear branch evolved as a functional mitochondrial gene until the split of the 2 species of chamois and as a typical pseudogene later on. We propose that the pseudogene originated from a highly divergent mitochondrial lineage that did not persist in the mitochondrion and transposed to the nucleus in a time close to speciation. The concurrence of highly differentiated lineages at speciation points to hybridization between highly divergent populations.