Seminal fluid proteins show striking effects on reproduction, involving 
manipulation of female behavior and physiology, mechanisms of sperm competition, 
and pathogen defense. Strong adaptive pressures are expected for such 
manifestations of sexual selection and host defense, but the extent of positive 
selection in seminal fluid proteins from divergent taxa is unknown. We 
identified adaptive evolution in primate seminal proteins using genomic 
resources in a tissue-specific study. We found extensive signatures of positive 
selection when comparing 161 human seminal fluid proteins and 2,858 
prostate-expressed genes to those in chimpanzee. Seven of eight outstanding 
genes yielded statistically significant evidence of positive selection when 
analyzed in divergent primates. Functional clues were gained through divergent 
analysis, including several cases of species-specific loss of function in 
copulatory plug genes, and statistically significant spatial clustering of 
positively selected sites near the active site of kallikrein 2. This study 
reveals previously unidentified positive selection in seven primate seminal 
proteins, and when considered with findings in Drosophila, indicates that 
extensive positive selection is found in seminal fluid across divergent 
taxonomic groups.