Zietsch & Santtila's study is not evidence against the by-product theory of female orgasm

► We contest Zietsch & Santtila's (2011, Animal Behaviour, 82, 1097-1101) conclusions for the evolution of female orgasm. ► Zietsch & Santtila used inappropriate comparisons of different orgasmic properties. ► Zietsch & Santtila's analyses relied on linking correlated morphology with correlated function. ► Lack of correlation fully expected under by-product view. ► Zietsch & Santtila's findings are irrelevant to the by-product account for female orgasm.