There are numerous complex issues here in the philosophy of so-called animal cognition or comparative ethology, but it seems to me that the burden of proof is with anyone who says no. The same issue arises, clearly, for human beings. So if we say that we do not know that the beagle feels love when he wags his tail and bays a bit and licks us and even gives us little nips behind the ears, and is obviously happy - more than happy - to see us, and delights in our presence, why would we not say the same about the human being doing these things, or their non-beagle equivalents? It's no good saying that he's doing it because we feed him. The same is true in the human case, but the manner of feeding is different, as is what is fed. It is difficult to imagine an ant loving us, but I think that is because there is no demonstration of affection from ants, no licking or running round in circles and so on. They would be ignoring us, if they were human and doing what they do. None of this is an assumption, though; it seems to be more of a common sense observation, but one that ignores false philosophical paths.
Read another response by Jonathan Westphal
Can we assume that our pet dogs feel love towards us?