how in the living fuck did onions even evolve to have a gas that makes your eyes burn when you cut them?

like yhe onion must be phtsically removed and then cut for the effect to happen, it is not like it increases it's survival chances, an onion tjat doesn't have gas is just as likely as to be cut as the one that doesnt have gas aince you dont know which is which until the onion is already dead

explain that one to me evolutionfags