Why are humans so competitive?

Hi guys i got something on my mind, have just been wondering,why human being are so upset with competition. It doesnt make sense to me, i have been told by my teachers that all living thing compete for space, food and shelter but i think it is more than that every thing we do always have competition in it even showing love.
    The one that i hate the most is competition in education it just anoying competing with people for knowledge which is surpose to be for every body.Even science knows that people have different IQ so i dont think grading exam is good.