If you have spent much time on the internet, you'll know at least one thing: our species loves cats.

How they feel about us is much less clear. Compared to our devoted dogs, cats seem pretty unconcerned with human affairs.

But it looks like our feline companions pay more attention than we give them credit for. They seem to be able to tell when we are happy.

New research has found the first strong evidence that cats are sensitive to human emotional gestures.

Moriah Galvan and Jennifer Vonk of Oakland University in Rochester, Michigan, US studied 12 cats and their owners. They found that the animals behaved differently when their owner was smiling compared to when they were frowning.

Cats can read human facial expressions, and they learn this ability over time

When faced with a smiling owner, the cats were significantly more likely to perform "positive" behaviours such as purring, rubbing or sitting on their owner's lap. They also seemed to want to spend more time close to their owner when they were smiling than when the owner was frowning.

The findings are published in the journal Animal Cognition.

The pattern was completely different when the 12 cats were presented with strangers, instead of their owners. In this setup, they showed the same amount of positive behaviour, regardless of whether the person was smiling or frowning.

The results suggest two things: cats can read human facial expressions, and they learn this ability over time.

We have known for a while that dogs are good at recognising human facial expressions. But this is the first convincing evidence that cats have the same capacity.

People are more likely to spoil a cat when they are in a good mood

Before this, only one other study has been done on the ability of cats to perceive human emotional expressions. Published in January 2015, it found ambiguous results.

Galvan and Vonk's finding suggests that cats are more in tune with human emotions than we thought.

That does not mean they feel empathy. It's more likely that the cats had learned to associate their owners' smiles with rewards: people are more likely to spoil a cat when they are in a good mood.

Still, even if cats do not truly understand our moods, the study still suggests that they can pick up on surprisingly nuanced human gestures.

It also suggests something more basic: they are interested in us.

"People care about whether cats really do understand and pay attention to their owners," says Vonk. "Our work shows that they may not be as indifferent as people accuse them of being."

Domestic cats first appeared around 10,000 years ago

It may have taken so long to discover cats' emotional intelligence because their responses are rather subtle. As well as obviously "positive" actions like purring or rubbing, Galvan and Vonk noticed that the cats adopted certain body positions, and ear and tail movements, that are associated with contentedness.

In contrast, scientists have known for several years that dogs respond differently to happy and angry faces. That is at least partly because their responses are more obvious. A 2011 study showed that dogs will actively avoid someone who appears angry, rather than just changing their body language.

The difference between dogs' and cats' responses to human emotions could be rooted in prehistory.

Dogs have been domesticated for a long time. A 2015 genetic study suggested that the process began over 30,000 years ago. In contrast, domestic cats first appeared around 10,000 years ago, probably in the Middle East.

We do not even know why they purr

Dogs' stronger responses to our emotional gestures could have arisen simply because they have had longer to adapt to life with humans.

But for now it is too early to draw conclusions. While there has been plenty of research into dogs' minds, there have been remarkably few studies of how cats respond to human gestures.

They may be our most popular pet but we still have a lot to learn about them: we do not even know why they purr. But this study might go some way to repairing cats' reputation for being uncaring. It may be that they simply do not show their affection for us as much as dogs do.