system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The bodies response to sea sickness or travel sickneas

I was listening to an old No Such Thing As A Fish podcast and they were discussing the theory that motion sickness might be and old response to stop our ancestors from climbing too high in trees, and the swaying motion from the weak branches would bring on motion sickness. In situations like this, or any other situation where it occurs, what purpose does throwing up serve? Why is this the body's response to these situations and not something else that doesn't waste precious resources and nutrients?
gpt
When you get sea/travel sick, it is due to what your eyes seeing (little/no movement) conflicting with what your inner ear is saying (movement).  You are traveling - and your balance systems know this - but your eyes are telling you everything is stationary (because you are looking at the inside of the vehicle).

This incongruence _also_ happens with some poisons, so our bodies default reactions when it senses this incongruence is "you've been poisoned - get everything out of the system ASAP".  This reaction evolved long before we had the kind of travel that would mimic the symptoms, and there isn't really and advantage (evolutionarily speaking) to getting rid of it, so the reaction remains.