Science

I definitely agree there, as most philosophical subjects don't really matter in a real sense. To me, though, this has some real implications regarding (pretty far in the future) AI development. If we were to say/prove humans have free will, that would be a potential bar to clear for when an "entity" is entitled to rights. It's all largely arbitrary, though, as (at least in the US) we aren't super rigorous to which animals are entitled to which rights. For instance, the Animal Welfare, which regulates when you have to use anesthesia, defines animals as

Animal means any live or dead dog, cat, nonhuman primate, guinea pig, hamster, rabbit, or any other warmblooded animal, which is being used, or is intended for use for research, teaching, testing, experimentation, or exhibition purposes, or as a pet. This term excludes birds, rats of the genus Rattus, and mice of the genus Mus, bred for use in research; horses not used for research purposes; and other farm animals, such as, but not limited to, livestock or poultry used or intended for use as food or fiber, or livestock or poultry used or intended for use for improving animal nutrition, breeding, management, or production efficiency, or for improving the quality of food or fiber. This term also excludes falconry. With respect to a dog, the term means all dogs, including those used for hunting, security, or breeding purposes