LÃ¼ke L, Tourmente M, Dopazo H, Serra F, Roldan E. Selective constraints on protamine 2 in primates and rodents. BMC Evol Biol. 2016;16:21 pubmed publisher
..However, sexual selection on its sequence may be difficult to detect until it is identified which sperm head phenotype (shape and size) confers advantages for sperm performance in different mammalian clades. ..