Lizard hemipenis

a Homalopsine snake hemipenis

pitviper hemipenis

wolf snake (a colubrid snake) hemipenis

Many species of different taxa whether vertebrate or other wise are distinguished by morphology of their sex organs – pit vipers are best distinguished by their hemipenis morphology. This is because the sex organs are important in retaining the species identity i.e. they remain conserved; but they may also be important drivers of speciation through sexual selection. Sexual section is not the same as natural selection, though it is a kind of natural selection.