A Question of Taste
Humans have five basic tastes: salty, sweet, sour, bitter and umami (savoury). Taste, along with smell, is one of our most ancient and important senses. It helps us decide what to eat and warns us of toxins in our food. You might be surprised then at the variability in taste across the animal kingdom. For example, cats and chickens have no sense of sweet, Giant Pandas have lost their taste for umami and vampire bats can’t taste bitter. In all cases this is probably because of changes to diet. Pandas are purely herbivorous and therefore have no need to taste meaty flavours, whilst cats and chickens are unlikely to come across many sweet tastes in their food.
Recent research however, has revealed one group of animals which have lost nearly all their sense of taste. Whale and dolphins live in an environment saturated with salt and new analysis of their genomes suggest they can only taste salty foods. Scientists from the Nanjing Normal University, China, and the Harvard Medical Centre, USA, took DNA samples from 12 species of cetacean. This included representatives from the baleen whales such as minkes and toothed whales like sperm whales and dolphins. The results showed that in all cases the genes responsible for four out of the five tastes were heavily damaged by mutation to the point that they could no longer be said to be functioning genes at all. Only salt receptors were still produced by a functioning gene. It wasn’t only the genes which were reduced however, and in some species the tongue’s epithelia itself was degenerate and contained a much reduced number of taste-buds.
The question of course is, why? The authors of the paper speculated that the habit of filtering or swallowing food whole may have rendered taste meaningless, so why retain a taste of salt at all? The answer may lie in their need to regulate the amount of salt in their bodies. All animals must control salt and so salt receptors becomes extremely important, especially in an environment as saline as the sea.
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