system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come that we can live without food for days, but get hungry within a few hours?
gpt
Survival is not thriving. Like you can survive on barely enough food for years, proper nutrition means you can maintain a healthy weight, expend energy on non essential things like exploration and procreation, when you have sufficient food your tribe is more likely to expand. So rather than wait till finding food is a matter of life or death, hunger reminds us to eat frequently, which means in times of plenty we are over nourished for the famine when there isn't as much to eat.