system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Is nodding for 'yes' and shaking the head for 'no' universal? Or is it a specific to certain cultures?
gpt
It isn't universal, but it IS extremely common across cultures, with by far the majority of cultures sharing a head nod as an indication of acceptance or agreement and a head shake indicating refusal or disagreement.  One of the common theories as to why this may be is that it comes from how babies use body language to indicate things before they speak.  When they are searching for a nipple to latch on to to get food they will scan up and down, and when they want to refuse food they will move their head to the side.