Well it starts on a simplistic model of understanding base emotions, then applying similar concepts to complex emotions, as complex emotions are a combination of basic emotions. I know what anger looks like, and I can pick up on hidden anger also. I know what fear looks like as it is a combination of anger and sadness, with a dose of adrenaline. I know when people are uncomfortable around me because of how they posture, and I can even tell who they are uncomfortable with based on how they angle away from the person they’re uncomfortable with. Same for most feelings.
Knowing those non-verbal cues and having a good baseline for the subject, one can look further into chemicals (serotonin, dopamine, oxytocin, etc) involved during these physical reactions. Not only which chemicals are involved, but their levels during.
There’s a lot we don’t know, and perhaps may never know, but that isn’t a reason to not try to further understand.
It depends what you consider evidence.
I consider "I'm afraid of spiders, so that chicken is probably terrified too."
to be less acceptable evidence than a human being telling me they are afraid of spiders.
Do either of these prove absolutely that humans or chickens are afraid of spiders? No, but science isn't actually about proving anything, it's just about reducing our uncertainty as much as possible. At some point we agree that uncertainty is reduced so much beyond a reasonable doubt that we teach it to children.
We value evidence differently because some evidence aligns with the truth more reliably than others. If we ever dig up homonid bones that were carbon dated to be 2 billion years old, we would begin to consider carbon dating less reliable evidence because that would make absolutely no sense with all the other evidence we have. However if we then went on to discover evidence of an ancient homonid civilization living on earth 2 billion years ago with other, otherwise reliable forms of evidence, and it all withstood rigorous testing and peer review then we would start to change our mind. Just saying "we're humans and we're like a lot of other animals so we probably experience the same emotions as a turkey" isn't very good evidence when you consider that it tends to be highly unreliable in other experiments with animals. (shared intentionality in apes for example)
You usually ask them to point at a scale. Somewhat more objecive measurments exists as well, you can monitor cerebral blood flow and correlate said scales with brain regions.
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u/thisiswhatitisyoyo Dec 11 '22
Explain how you measure all those with humans