Science

I think it's very much an artefact of religious attitudes at the time science started advancing during the Industrial Revolution, which held up humans as being superior to animals (and also that people before the Industrial Revolution were ignorant and unenlightened). Given that we have legal records from the centuries before that, where animals were held to have legal/moral equivalency to humans (this includes incidences of animals being punished for crimes, of course, but there's also a case of a court ruling in favour of weevils having rights over a particular field, so the farmer had to let them have it - the record of whether the weevils abided by this agreement was... eaten by weevils), I suspect that back then people were a lot more open to the idea that animals had many of the same capabilities as us. Christianity, especially the "humans have dominion over everything else" strains of it that we've had for the last 150 years or so, likely does not reflect the attitude of all humans for the entirety of history - although of course in the past, people didn't have the scientific knowledge needed to prove it conclusively.