The Love/Hate Impulse

One of the most amazing things that we as humans have in us is what we've call love. It's not an emotion that is needed for survival, that emotion is lust. So why are we embedded with such an overwhelming feeling such as love if it is not a necessity for us to survive? It's such a complex emotion that changes many people's life each day. Love can bind two people together, while it's opposite condition will further the distance. I can say I'm pretty sure that I've felt the feeling of love and hate so far in life. Both of which are very complex and intense emotions. Hate does not aid the survival of life either, so why do we feel both of these emotions? An argument can be made talking about why we feel these emotions involving Jesus and the Devil, but since such things dealing with religion are perceptive, and change from person to person, it's save to say that argument is perceptive to your own belief on religion with heaven or hell. How did such complex emotions come to be?