The number of humps camels and alpacas have may play a role in how well they store and break down fat. A comparison of the animals’ genomes shows that the genes associated with energy use evolved more quickly in humped camels than in non-humped alpacas. There are even differences between double-humped bactrian camels and single-humped dromedary camels, hinting that the animals’ fat metabolisms may be influenced by their hump number, researchers report October 21 in Nature Communications.