Not every perspective is provable to everyone, attitudes are influenced by positions
People don’t see themselves under primarily biological terms, they say their culture and their social life is a proof of being more than just driven by instinctual biologically explainable factors. They say the have their mind, their spirit, their thinking.
A perspectival shift to not see nonhumanity under biological terms primarily, does not need a proof, it needs the will to take another stance towards our environment. Seeing nonhumanity non-biologically and as individuations of Life in its own merits, seems to be unwanted and is treated almost like a form of “blasphemy” against an almighty scientifical system of categorization in our current societies and their Zeitgeists. Stances, positions are however not a matter of proof so much, but much more of choosing a specific perhaps differing standpoint and a perhaps fundamentally different angle of perspective – and that might be one that can’t be proven to the other side, since their outlook is so much predetermined by their own interest.
In the case of evaluating the own interest and the interest of others, operating with proof to privilege one side while disadvantaging the other, forces us to think in one direction only. We assume that it is objectively proven or probable that for instance nonhumans lose less if they die compared to humans, or that it is objectively provable that the reasoning of nonhumans can be behaviouristically determined and would not be autonomous. Proof selects a supposedly objective framework of reference, if you chose another framework of reference you come to a different kind of conclusion: an example, the starkest one perhaps is the different perspective an ecocentric person choses versus a humancentric one at a given moment.