Only 3 per cent of all the mammals in the world are monogamous in nature. Humans are considered to be one of those few species. And yet, infidelity is fairly common amongst humans. What is it that makes some of us go against our nature and cheat on our partners? Why is it that some people find it hard to stay loyal to one partner? There’s finally a convincing answer to that question, thanks to this new scientific theory according to which, some people are simply born cheaters.