That cute kitten sitting innocuously on your lap can never be truly tamed. John Bradshaw investigates the evolutionary quirks behind one of the UK’s favourite pets.
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Pet cats may be domestic animals, but they’re not fully domesticated. The cat family – felids – evolved from the other carnivora about 11 million years ago, and apart from size, have not altered a great deal since then, such that even today they are all obviously cat-like. Domestic cats still have much in common with their wild cousins, from the noble lion down to the tiny (and very rare) kodkod, found in Chile. So the question is, how similar is your cute kitty to a tiger?
Millions of years ago, a dozen or so genetic changes took place in the ancestor of all of today’s felids, which have locked them into eating meat ever since. All cats, from tabby to tiger, require high levels of animal protein in their diet – protein from plants lacks certan amino acids, such as taurine, that cats need but other mammals (including ourselves) do not.
Cats can’t make their own prostaglandins – hormones essential to reproduction – and so need to get these from meat. Compared to other mammals, all cats need large amounts of several vitamins, such as niacin, thiamine and retinol, which are more easily extracted from meat than from plants. And because they don’t need to tell the difference between ripe and unripe fruit, they’ve lost the ability to taste sugars. They have adapted their ‘sweet’ taste buds for distinguishing between different flavours in meat – which is why pet cats sometimes walk away from food that seems fine to their owners.
This knowledge has only come to light in the past 40 years, benefiting not only pet cats but also the captive breeding of endangered felids such as the clouded leopard. As many of two-thirds of all felid species are endangered.
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The domestic cat’s DNA was first sequenced in 2007. This has since been repeated for the European wildcat, Felis silvestris silvestris, which is first cousin to the domestic cat’s ancestor, the Arabian wildcat Felis silvestris lybica. The European and Arabian wildcats separated about 200,000 years ago, whereas it has only been 10,000 years since the domestic cat Felis silvestris catus emerged as a distinct subspecies. Once the first Arabian wildcat is sequenced, we should be able to pinpoint the crucial differences that make it possible for domestic cats to socialise with us, something wildcats find impossible.
Most cats lead solitary lives, kept apart by the need to monopolise a hunting area. The lion is the only species in which males and females live together in prides, which they can do because they hunt prey that is large enough to feed many lions, not just one.
Female cheetahs are solitary, but males sometimes live as a group. The domestic cat is the only felid species in which males are solitary and females are sociable: mothers and daughters often raise their kittens together. Pet cats show affection for us as they do with other cats – raising their tails upright and attempting to groom us – so perhaps they perceive people as just large, two-legged felids.
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Of all fields, only the cheetah specialises in hunting by day, and so has fairly small eyes. Many of the larger cats have slightly larger eyes that are more sensitive than ours, allowing them to hunt by moonlight as well as during the day. But most of the smaller species, including the domestic cat, are mainly nocturnal in the wild. So that they can gather enough light to see by, their eyes are huge relative to their skulls – a domestic cat’s eyes are almost as big as ours.
Inside the eye, the retina is about six times as sensitive as ours, and wired to the brain in such a way as to maximise sensitivity, at the expense of sharpness. All felids also possess a reflective layer behind the retina, the tapetum, that further increases sensitivity while at the same time producing their distinctive green ‘eye-shine’ when caught in a torch-beam.
Cats were originally domesticated to keep mice and rats away from our farms, homes and grain stores, and although nowadays we don’t generally encourage our pet cats to do this, inside their heads they’re still hunters.
The way they ‘play’ demonstrates this fact perfectly. When they’re playing with small toys, they use the same techniques they use on mice, such as pouncing, and grasping in the mouth. Larger toys, however, are attacked not with the teeth but with all four sets of claws – reflecting the need to hold a rat, which can be a formidable foe, at arms’ length.
Even more revealing is the effect of hunger on play: a pet cat that hasn’t eaten overnight plays much more intensely than when it’s just had breakfast, as if it believes that ripping apart a felt mouse will actually produce a meal.
Predators rarely live in close proximity, and see or hear each other only rarely, so they have to communicate by smell. Lions, tigers and domestic cats deposit urine around their territories, and they also rub their cheeks on prominent landmarks, leaving behind scent from their skin glands. All cats also possess a second ‘nose’ – Jacobson’s organ – purely for analysing the smell of other cats. This lies between the nostrils and the roof of the mouth. The outward sign that it’s being brought into play in lions and tigers is a curling of the top lip, a posture referred to as ‘Flehmen’. Domestic cats instead they look as though they’re going into a brief trance. Muscles around the Jacobson’s organ pump a drop of fluid into the mouth, where it dissolves some of the odour being sampled, before being drawn back up into the organ for analysis.
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