Olfactory receptors (ORs) detect odorants and are vital for the survival of most mammals. In this study, the researchers developed a new phylogeny-based method to analyse >10,000 OR genes from 13 placental mammals to determine the extent of OR variability across species. Some of the 781 orthologous gene groups were expanded in a lineage-specific manner and, interestingly, only 3 of these gene groups were conserved across species. Of the 13 species, African elephants have the largest repertoire of functional OR genes (~2,000 genes) — 5 times as many as those of humans.