We now know scientifically that fish feel pain (they have nociceptors and change behavior when given analgesics). We know that elephants suffer PTSD. We know that isolation drives social primates insane. The neuroscience of consciousness has demolished Descartes’ notion that animals are automata. For welfarists, this data provides the metrics for reform: how much space does a hen need to dustbathe? What stunning method renders a cow insensible instantly?
Footnotes: This article is an educational overview. For specific legal advice or local advocacy groups, please consult your regional animal protection organizations. We now know scientifically that fish feel pain