system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the brain divided in two parts?
gpt
This is due to something called "bilateral symmetry", a basic body plan that developed extremely early in our evolutionary history. It probably comes down to the benefits of having a spare organ in case of injury, such as a extra arm to feed oneself or an extra eye. Greater levels of symmetry have developed as well but having two seems to avoid an injury being invariably fatal while not spending too many resources on redundant features.