I agree that emotions reading of primates can turn wrong when taken out of context (even the reading of human facial expression can be confusing out of context)

I agree that emotions reading of primates can turn wrong when taken out of context (even the reading of human facial expression can be confusing out of context). But in context, you'll quickly (and sometimes painfully) learn the meaning of their facial expressions, and other affective displays. Also, tears are not necessary to cry. In your source, scientists prefer to conservatively talk about "distress vocalizations" instead of crying. But that's necessary because they are so similar in the first place! That's my point: they express their distress! In everyday life (not writing a paper), I'd just say that "this ape is crying because her baby died". Heck, even my dog, I'd say that he's crying. I don't care that there are no tears. They have a mammalian limbic system, and the rewards it contextualizes have to be evolutionarily sensible! Btw, and I know that's not a strong argument, but my eyes don't produce tears (following some medication). Does it downgrade my crying into a distress vocalization? If not, is it because you think that you know how I am feeling? How I am thinking? really? How do you know that? PS: as a_bonobo yourself, you know that what I say makes sense ;).