a surprisingly wide range of species display something similar in some cases, though it is hard to say how aware they are of it, or how important it is to their lives.
So if our non-human ancestors exhibited this behaviour, but did not actually have a theory of mind, how come we can say that our equivalent behaviour does flow from having a theory of mind? That makes no sense. So we develop the behaviour first, then we develop a theory of mind, and it’s a pure co-incidence that the behaviour flowing from having a theory of mind just so happens to be completely indistinguishable, even though the cause is completely different? I just don't see how that can be credible.
The only coherent account, to me, is that the behaviour we have which we believe flows from having a theory of mind, if exhibited by other animals, must be evidence that they posses a theory of mind as well.
Having said that, one can still consider when, where, how and how often it evolved. For example, there are many species that cache food. Some (some squirrels and also scrub jays, for example) will either only pretend to cache the food they are carrying, or move it later, if they notice they are being observed. Is that an application of a general theory of mind at work, or an instinct that evolved for one particular circumstance? As far as the ethical treatment of animals is concerned, I have no objection to assuming the former, but if we want a scientific understanding of what is really going on, that assumption cannot be made without further evidence.
What you are overlooking, I think, is that there are several possible explanations for the externally-observable behavior, and once you recognize that, there should be no paradox. In our case, we, as privileged observers of our own minds, can see our theory of mind at work, and, through language, we can talk to other people and ask how it seems to them. Neither of these lines of inquiry are an option when it comes to studying other species.
There is an interesting parallel in ethics: some people are well-behaved because they are fearful of punishment or ostracism, while some do so out of respect for other people. You can't always tell motive from actions alone.
With species like squirrels that are more remotely related to us, there is more scope for an argument of parallel evolution, sure. Maybe their similar behaviour developed independently and has a different cause especially when other mammals do not exhibit this behaviour.
With our much closer relatives such as apes though that exhibit so many more behaviours that are very close to ours it’s much less plausible. If all of them exhibit a common pattern of social behaviour with ourselves, arguing all of them could have independently developed this behaviour separately from us and each other, to appear indistinguishable, that seems highly implausible.
Even with squirrels though, as mammals they exhibit many behaviours common to all mammals. Behaviours we exhibit as well. So if all mammals have these behaviours and we do too, if our behaviour has a different cause, at some point our ancestors must have switched from exhibiting the behaviour due to the common mamalian cause to exhibiting it due to this new cause unique to us. I don’t find that account very plausible either.
Did our ancestors stop exhibiting this behaviour first, then develop new neurological mechanisms that happened to replace the lost behaviours? When did that happen, before or after we diverged from other apes? Maybe they have these behaviour for the same reason as us but other mammals don’t? Did we develop a parallel mechanism and the behaviour transitioned to the new causal mechanism? I’d expect to see some residual evidence in our neurology or behavioural patterns of that having happened.
>Even with squirrels though, as mammals they exhibit many behaviours common to all mammals. Behaviours we exhibit as well. So if all mammals have these behaviours and we do too...
Here you are combining speculation with an argument from the general to the specific. There are some behaviors common to all mammals, but are there any theory-of-mind-like behaviors in that category? No, so the rest of that paragraph and the one following are built on a false premise.
I am no expert, but FWIW, I happen to think that apes, or at least chimpanzees and orangutans, do have a nascent theory of mind, and that it was more developed in the various hominins that are now extinct.
That doesn’t mean I have to assign apes moral equivalence to humans. Rights also imply responsibilities and apes are not capable of fulfilling the responsibilities of a human being. But then you hit the argument that some human beings aren’t capable of fulfilling those responsibilities either. Well, we are communal and social beings. We have a tendency to treat members of our community differently from outsiders, and generally better. For example we treat citizens differently from non-citizens. Family differently from non-family. I think it’s reasonable to treat humans differently from non-humans and grant them enhanced rights.
However I do still accept our common biology and experiential and emotional lives with some animals. I can accept that when an ape or a human sit watching a sunset, relaxing and not actively thinking about anything, that they have fundamentally the same kind of experience. I think that reasonably extends to a bias against causing unnecessary suffering for example. How we treat others and how we treat animals says something about our character.