Our findings illustrate that increasing genomic complexity of the Mup gene family is not evolutionarily isolated, but is instead a recurring mechanism of generating coding diversity consistent with a species-specific function in mammals.

— Logan DW, Marton TF, Stowers L (2008) Species Specificity in Major Urinary Proteins by Parallel Evolution. PLoS ONE 3(9): e3280. doi:10.1371/journal.pone.0003280

(See “MHC isn’t sexy after all” for more information.)