Theory on why cats are obligate carnivores (hyper-carnivores)

James Sanderson and Patrick Watson in their book Small Wild Cats make what I think is a very interesting suggestion or theory as to why all members of the Felidae family i.e. all cats, are hyper-carnivores meaning that they can only eat meat and that their digestive systems and anatomy have evolved over millions of years to deal with this extreme diet.

Carnivore diet
Carnivore diet for wild cats at zoos. Image in public domain.
Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

By human standards it is an unbalanced diet. For the cat it is perfect but why did this happen? It’s a peculiarity although people who know cats well fully accept it but it bears a little bit of scrutiny.

Those who know cats will also know that the domestic cat and other members of the cat family cannot taste sweetness because of a genetic mutation, a kind of defect that took place many millions of years ago (perhaps 30 million years ago) before the family of cats split up into eight lineages.

Cats evolved from a fierce sabre-toothed predator that prowled North America 42 million years ago, according to new research
Cats evolved from a fierce sabre-toothed predator that prowled North America 42 million years ago, according to new research. San Diego Natural History Museum SWNS.

In the words of Sanderson and Watson: “In 2005, scientists discovered that all cats lack one of a pair of proteins required to sense sweetness”. In other words, the cat’s tongue does not contain receptors that can detect sweetness but they can detect the opposite – the taste at the other end of the spectrum – namely bitterness because things that taste bitter are often toxins to the cat. That’s why, incidentally, they leave the bile duct uneaten when they have consumed a mouse. Bile is a bitter substance.

Is this all that is left of a mouse when your cat eats one?
Is this all that is left of a mouse when your cat eats one? The bile duct. It is bitter. Photo: MikeB

And the taste of sweetness can be found in plants because of the chemical process called photosynthesis in which plants convert carbon dioxide into sugars. Photosynthesis occurs in the leaves of plants. It needs chlorophyll and light energy. The chlorophyll helps to convert carbon dioxide and water into oxygen and glucose. Glucose acts as a vital source of food for the plant. The fact that trees absorb carbon dioxide is a vital element in fighting global warming. It is the reason why (and I’m diverging from the topic here) it’s important that trees are not cut down as has been occurring in vast numbers in the Amazon Basin.

Okay, so cats can’t taste sweetness but they like the taste of flash and therefore they eat flesh and therefore they kill animals to eat flesh to sustain themselves. That’s the process by which it has been suggested that cats became hyper-carnivores and not omnivores such as the fox.

That being said, cats do eat some grass and there are various theories as to why they do. Some wild cat species such as the snow leopard eat quite a lot of vegetation. My theory on that is still leopards live at high altitudes and they need to boost the way their blood carries oxygen around their bodies in haemoglobin and eating vegetation helps to boost the oxygen content in the blood. Just a theory.

Although cats are strict carnivores it is not a total, absolute black and white situation. They do eat vegetation and it depends on the species of cat as to how much vegetation they eat. It has to be surmised, however, that they don’t like the taste because there is no taste or almost no taste. They eat vegetation for health and survival reasons. It must be a bit like medicine to the cat whereas eating flesh is pleasurable.

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