Aug 12, 2010 10:48 GMT  ·  By

Even though all animals have some sort of chemical sense, evolution has differentiated it depending on the eating habits of each species.

Taste and smell are the oldest chemical senses and they are crucial as they help knowing if something is good to eat or not.

Smell detects chemicals at a distance and can make many distinctions but it cannot detect ions that need water to dissolve and that's where taste comes in.

Invertebrates have special cells that are used as chemical senses, like flies that taste through their feet and proboscis, and all vertebrates have tongues thus taste buds.

Dr Susan Hemsley, a senior lecturer in veterinary anatomy and histology at the University of Sydney, interviewed for ABC Science, said that not all animals taste the same things, as they usually have taste buds depending on what they mostly eat.

She said that even if it is generally thought that things taste to us the same way they do for animals, there are some exceptions, even with the similarity of the molecular mechanisms.

“Cats can't taste sweet things, it's an evolutionary trait that all members of the cat family have lost, and some species of monkey can't taste artificial sweeteners, but do taste natural sugars,” she adds.

The 8 to 10 thousand taste buds on human tongues usually last about 10 to 14 days before being replaced and other mammals also have a big number of taste buds, especially on the tongue and pallet.

Cows are herbivores and they have around 25 thousand taste buds, pigs are omnivores and they have about 15 thousand and carnivores have the fewest of them all.

The explanation is very simple and quite logical: “herbivores have so many taste buds because they need to be able to tell if a specific plant contains dangerous toxins, on the other hand unless you're eating cane toads, carnivore's diets are usually fairly safe.”

Hemsley added that “birds have far fewer taste buds than mammals, chickens only have around 30, but parrots have several hundred, which is more than most other birds, and cockatiels can even discriminate between salt, sugar and acids.”

“Fish have lots of taste buds, both in their mouths and on their skin, especially along their lateral lines,” and many reptiles like lizards and snakes use their tongue to detect taste and smell chemicals in the air by transporting then into a pit in the roof of the mouth called the Jacobson's organ.

For humans, taste is given but the taste receptor cells grouped in clusters of up to 150, called taste buds that are usually found on small pegs of epithelium on the tongue called papillae.

The taste buds identify five primary flavors: salty, sour, sweet, bitter and umami; the salty flavor regulates the diet for electrolyte balance, sour usually identifies acids, sweet – energy-rich nutrients, bitter generally indicates toxins and finally, umami, that is the taste of the amino acids in meats and cheese.