WOLFSON—LEVY—Cruelty to animals is unjust because of the suffering that it causes them, not because of any deprivation that it causes humans. Pain is pain – whether it is experienced by a human or a nonhuman. And lest anybody doubt this intuitively obvious claim, we have ample scientific evidence for it. Through evolution, nonhuman and human animals alike acquired something that plants and trees never did: nervous systems. These nervous systems explain why not only humans but also nonhumans exhibit both fear and pain-avoidance behavior (for example, fleeing and vocalizations such as screaming and groaning).