Do animals taste the same things as humans?

In evolutionary terms, the chemical senses — taste and smell — are the oldest. They're important because they help indicate whether something is good to eat or whether it's bad for you.

Sweet things often indicate an easy source of energy, while bitterness can be a sign of something poisonous.

Smell lets you detect chemicals at a distance and it draws in the finer distinctions, but isn't very good at detecting ions that have to be dissolved in water like saltiness, sweetness, or sourness.

Taste, on the other hand, lets you get up close and personal.

All animals have some sort of chemical senses, from critters as small as single cell amoebas which sense specific chemicals and move towards them, through to elephants and even whales.

Invertebrates such as insects use cells devoted to chemical senses which are the direct evolutionary equivalents of mammal taste buds. Flies, for example, taste through their feet and proboscis.

Vertebrates, on the other hand, all have tongues, and all tongues have taste buds.

But not all animals taste the same things, says Dr Susan Hemsley senior lecturer in veterinary anatomy and histology at the University of Sydney.

"Different species have different taste buds specialised to detect the things they're most interested in.

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How taste buds work

In humans, the sense of taste comes from taste receptors cells which are bundled together in clusters of up to 150. It's these clusters which we call taste buds and they're usually most prevalent on tiny pegs of epithelium on the tongue called papillae.

Interwoven among the taste receptor cells is a network of sensory nerve fibre endings which are stimulated (depolarised) by the release of neurotransmitter molecules from the receptor cells.

This stimulation (depolarisation) is transmitted through the nerves to the brain.

There are five primary flavours:

• Salty, which allows modulating the diet for electrolyte balance.
• Sour, which usually indicates acids.
• Sweet, which indicates energy-rich nutrients.
• Bitter, which can indicate toxins.
• Umami, which is the taste of amino acids such as meats and cheese.

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Humans versus animals

It's generally thought that things taste the same to us as they do to other animals, says Hemmsley.

"The molecular mechanisms appear to be similar. What's sweet to us, also tastes sweet to a mouse."

There are, however, some exceptions.

"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 says.

Humans have about 8 to 10 thousand taste buds on their tongue, that usually only last about 10 to 14 days before being replaced.

Other mammals have lots of taste buds, mostly on their tongue and pallet.

Herbivores like cows have around 25 thousand, omnivores like pigs around 15 thousand and carnivores generally have the fewest.

"Herbivores have so many taste buds because they need to be able to tell if a specific plant contains dangerous toxins," she says.

"On the other hand unless you're eating cane toads, carnivore's diets are usually fairly safe."

"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" according to Hemsley.

"Fish have lots of taste buds, both in their mouths and on their skin, especially along their lateral lines."

Many reptiles such as snakes and lizards use their tongues to detect taste and smell chemicals by transporting molecules to a pit in the roof of the mouth called a Jacobson's organ. But unfortunately, many Australian snakes and lizards haven't developed an evolutionary warning system against cane toads.

Dr Susan Hemsley is a senior lecturer in veterinary anatomy and histology at the University of Sydney. She was interviewed by Stuart Gary.