system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is smiling a show of friendliness in humans when showing teeth a sign of aggression in most animals?
gpt
In primates showing teeth held together like you do in a smile is a sign of submission, not aggression. In humans smiling likely evolved from this as a sign of peace/not intending harm, especially when combined with laughter.