▪ Abstract  The evolution of proteins involved in reproduction is only now beginning to be studied. A reoccurring observation is the rapid evolution of the molecules mediating reproductive events following the release of gametes. We review the examples where rapid evolution of reproductive proteins has been documented, covering taxa ranging from diatoms to humans. The selective pressures causing this divergence remain unknown, but several hypotheses are presented. The functional consequences of this rapid divergence could be involved in speciation.