I wouldn't say "plenty" - few primates, dolphins, orcas, elephants, and, strangely, magpies. But the grounds for that claim are shaky for some of them, the only 3 species we are 100% sure about are chimpanzees, orangutans, and humans. Magpies, for example, require "a training" (whatever that means).
Probably cause we've only tested a few, not that it matters though. Humans take a pretty long time to recognize themselves in the mirror. I wonder if the mirror test would change if we would expose the animals for a almost a year before doing the test, just like humans.
That said even ants pass the test, i.e. they were recently(2015) tested.
But the whole thing can be characterized as: "Let me make up a random test, according to my personal opinion of what defines cognition and then see if a random animal I choose passes it".
Every couple of years we have requests of slews of psychology papers requested to be invalidated because they're unreproducible.
> But the whole thing can be characterized as: "Let me make up a random test, according to my personal opinion of what defines cognition and then see if a random animal I choose passes it".
But of course! How do we know that humans are, indeed, the smartest? What if we've been failing every single test that mice have been throwing at us over the past millennia, and they wonder why we are so dumb?
(This is a reference to The Hitchhiker's Guide to the Galaxy in case you're wondering if I've gone mad. Not that one wouldn't presuppose the other :)
Dolphins and elephants are famous examples, most primates as well. Even many birds show levels of self awareness and theory of mind (they know the difference between what they know and what others know)
In fact there is a popular theory[1] that bird intelligence evolved because of the way their social structures work. Birds mate for life but they cheat. Every bird wants their partner to be loyal and itself to sex as many other birds as possible.
This means birds have to keep track of who can and can't see them cheat, who knows and who doesn't. There's even evidence that they rat each other out (2nd degree info) if they think there's a reward to be had. All of this requires immense intelligence, which happens to prove useful in other contexts.
There's also a bird species who does this with food caches. Easier to steal from others than to build their own so a plethora of deceptive tactics developed to ensure others can't see where you're storing those delicious nuts. Complete with fake caches, lying, and espionage.
There is proof, and you can find lots of studies and papers on it. HN is a bit cultish and likes to think that humans are far above every other creature on the planet in importance.
