system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we get crushes?
gpt
Mating instinct. 

One of your most primal urges is the urge to breed (or at least perform the reproductive act). Humans, along with other social animals, have this urge strongly linked with pair bonding, as having 2 active parents for young offspring greatly increases their chances of survival.