Many meat-eating animals have lost their ability to taste sugars over the course of evolution. Sea mammals, spotted hyenas and other carnivores have all shed a working copy of a gene that encodes a ‘taste receptor’ that senses sugars.
Most mammals, including humans, are equipped with taste receptors that detect salty, sour, sweet, bitter and savoury foods. But past studies suggest that some animals lack certain taste receptors. Felines such as house cats, tigers and cheetahs do not favour sugar water over plain water, for example, and they all possess an identical mutation in a gene called Tas1r2 that renders the sweet-taste receptor inactive.
DNA from 12 members of the order Carnivora, including spotted hyenas, a cat-like creature from Madagascar called a fossa, a civet called a banded linsang and several species of sea mammal was extracted and studied. Seven of the species contained a broken copy of the gene encoding the sugar taste receptor, but the exact mutations often differed among them. For instance, fur seals and sea lions share many mutations in Tas1r2, but the more distantly related Pacific harbour seal lost its sense of sweetness through different mutations in that gene. The species of land mammals that the researchers examined each contained unique Tas1r2 mutations.
That the mutations are not identical across species suggests that carnivores have independently lost their ability to detect sugars, an example of convergent evolution. Plants are the major source of dietary sugars, so it makes sense that animals that consume mainly meat or fish could live without a working sugar taste receptor. There is no evidence, however, that carnivores benefit from losing the ability to sense sugars, and some animals such as the insect-eating aardwolf, which is closely related to hyenas, and the omnivorous spectacled bear have working copies of the genes that encode the sweet taste receptors.