A new theory has suggested that we could be actually manipulating others when we cry or show anger .an
John Tooby, an evolutionary psychologist at the University of California, Santa Barbara, claims that our emotions have evolved as tools to manipulate others into cooperating with us.
Anger, he says, has as much to do with cooperation as with conflict, and emotions are used to prod others into cooperating in the long term.
But if they gave you the same amount of money not as a favour but to avoid paying a penalty, you wouldn't feel grateful.
You show gratitude not when someone benefits you, but when their dial is set higher than you expect, and this signals that you plan to turn yours up in response.
Another study revealed that stronger men and more attractive women were quicker to anger - as they have a stronger sense of entitlement.
Not everyone is convinced by Tooby's theory though.
"Whether [anger] constitutes some form of negotiation is a just-so story. They certainly don't have any strong evidence to support that claim," New Scientist quoted Michael Lewis, a developmental psychologist at the Robert Wood Johnson Medical School in New Brunswick, New Jersey, as saying.