Unsweetened cats, as described in PLoS July 2005, ScienceNOW 25 July 2005 and BBC News 1 August 2005.

Cat owners have known for a long time that cats are not attracted to sweet food. Now the reason for this has been found by a group of scientists at the Monell Chemical Senses Centre, Philadelphia, USA, who have analysed genes for taste in cats. The sensation of sweetness occurs when molecules of sugar or similar substances impinge on a receptor – a large protein on the surface of cells in the tongue.

In mammals the receptor is made from two protein sub-units, which are made from instructions carried on two genes named Tas1r2 and Tas1r3. The research team looked for these genes in cats and found both of them, but one does work properly. Tas1r2 has 247 DNA letters missing in one place and inappropriate “stop” instructions in other parts. This means cat taste bud cells cannot make the protein coded by this gene, and therefore cannot make the receptor for sweet taste. As a result cats cannot taste sweet things.

The defective gene is not only found in domestic cats, but also in cheetahs and tigers. The scientists concluded “this molecular change was very likely an important event in the evolution of the cat’s carnivorous behaviour” and they are planning to study “related animals, such as the hyena and mongoose, to help trace when and why sweet taste receptors became lost in the evolutionary process.”


Editorial Comment: A change from a functioning gene to a defunct gene is the opposite of evolution, i.e. it is a decrease in complexity, not the addition of a new characteristic. The finding of this defunct gene may strengthen the case that domestic cats are descended from tigers, but the results of the gene study can be better explained by Biblical history than evolution. Genesis 1:30 tells us that all animals, including cats were originally made to eat plants. As many plant foods have a sweet component, it makes sense that all plant eaters (cats included) would have had any genes needed to taste sweetness.

After Noah’s flood many animals, including cats, became carnivores and vegetables (and hence sweet foods) became less important in their diet. Therefore, when one of the ancestral cat’s genes for the sweet receptor was damaged it did not affect the now carnivorous cat’s ability to survive, so it has remained in their descendants to this day.

In the past we have upset many dog owners by pointing out that most domestic dogs are degenerate mutants. Now we can say the same thing about cats!

Sweet Cat Follow Up

Sweet cat follow up: after the article on the defunct sweetness receptor in cats (above) where we reported that a gene for the sugar detecting taste receptor in cats is broken and therefore cats cannot taste sweetness in foods a reader from Gages Lake, Illinois, USA wrote to us: “I have a newly-diagnosed diabetic cat. When I was afraid she’d been overdosed on insulin recently, I offered her Karo (corn) syrup, and she licked it up eagerly. She would likely have licked up much more, if I’d let her. She then seemed to feel much better. So, it appears that cats who are diabetics can tell that the syrup is sweet and should supply blood sugar. Hmm.”

Editorial Comment: Even if the cat couldn’t taste the sweetness, corn syrup has many other chemicals in it, so it would still some kind of flavour that could be tasted. Sugar is rapidly absorbed into the blood and the cat would quickly sense that the corn syrup drink was doing it good, and would associate that flavour with feeling better, and want more.

When they are unwell, cats and other carnivores are known to seek out plants that contain chemicals that help them get well again. Animals can be very good at self-medication, which involves the need for many pre-existent designed feedback mechanisms.

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