Why do humans and dogs smile but cats don’t? Firstly, I am not sure that dogs do smile but I’ll concentrate on humans and cats, two species that I know well.
Note: these are my thoughts because the experts don’t talk about cat smiles. If you have different ideas please leave a comment – thanks.
Cats smile in a different way
Cats do smile but they don’t use their faces (but see section on facial expressions below). They use their voices in their purr, their tail in their tail-up position and their noses in the nose touch. These are all feline ways to smile if we agree that a major purpose of the smile in humans is a friendly, non-threatening greeting.
The great Charles Darwin suggested that the human smile has evolved from teeth baring in primates. In primates teeth baring means a show force but in humans it has evolved to tell the other person that you are not a threat and friendly. In the West, when we greet someone we shake hands in and smile. We want to start the relationship on a friendly footing.
Of course the human smile means more than this. It is also reflects how we feel. When we greet with a smile it is habitual almost forced behavior a lot of the time but it serves a purpose. When we are content and we smile it tells others our feelings of happiness.
In cats, the purr does this. The cat’s purr both indicates contentment and like the human smile it can be used in appeasement by a subordinate animal towards a dominant one. Purring reduces the likelihood of an attack. Used this way the purr is not far from the greeting smile of humans. Kittens purr when suckling, which signals to their mother that all is well. It acts as a smile. Note: feline purring has other purposes too, which I discuss on other pages.
The feline tail-up is used to signal friendliness when meeting another cat. The nose touch is part of a friendly greeting. It is a bit like a handshake or a pat on the back. This is also similar to the smile. In fact humans often smile when shaking hands with a person they have just met.
My conclusion is that domestic cats don’t smile like humans because other methods have evolved as mentioned. Sometimes cats look as if they are smiling. This is because their face is built that way. The Chartreux is one of those cats famous for their smiling face. But this is not a genuine smile.
Feline facial expressions
My experience of feline facial expressions is that they are very muted and almost invisible but they can convey distress and chronic pain for instance. Conversely, it is possible that a cat might smile like a person but I am not convinced at the moment.
The well regarded book Cat Sense by Dr Bradshaw does not mention the smile. It is nowhere to be found in the book, which I think it significant. However, Bradshaw discusses the purr and its many uses. He writes:
“….each cat simply learns that purring under certain circumstances makes life run more smoothly.”
You can say exactly the same thing about the human smile.