system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do almost all animals seem to like scratches?
gpt
For social animals like humans and apes, grooming is a social adaptation that was used to bond with the tribe and was beneficial for removing parasites. For less social animals, it’s still a way of staying clean. Animals that don’t groom each other will still rub against trees or whatever to get things off their fur. Because removing dirt and parasites was an evolutionary advantage that promotes survival, the brain evolved to reward this type of behavior, making it feel good even to animals that don’t necessarily scratch each other in the wild. This is especially obvious when you consider where we like to be scratched (for humans, our backs, or for cats it’s often right by their tail). They’re the areas we can’t reach on our own.