Researchers have developed a formula to pinpoint whether a person is selfish or intuitively kind.

A team at Yale University sought to explore why some people seem to be intuitively kind to strangers, while others weighed up the personal benefits before acting.

They also wanted to answer whether people must work to stop their selfish impulses or if self-interested deliberation restrains an intuitive desire to co-operate.

The study concluded that those who weighed up whether they will receive a reward before showing kindness were more likely to avoiding helping others.

To make their findings, the researchers asked an undisclosed number of participants to play prisoner’s dilemma games: some ending in rewards, and some not.

The data was then related to evolution game theory, which uses mathematical equations to analyse decision making processes.

The evidence showed that participants who relied on their instinct in their decisions were more likely to come from a supportive environment.

On the contrary, those respondents who strategised how they would benefit before helping were more likely to have had bad past experiences.

Therefore, selfishness spreads as people learn as people learn that this is the msot beneficial way to respond when confronted with aiding another, the researchers concluded.

The researchers hope that the study will shed light into how humans think, and social decision making.

"Our model predicts that they’ll develop an instinct to be selfish and won’t ever deliberate," Bear told Medical Daily.

"In other words, they won’t ever change their instinct to be selfish and switch over to cooperation after deliberating."

The research follows a 2013 paper published in the journal 'Nature' which concluded that populations who co-operate are more successful than selfish ones in the long term.

"We found evolution will punish you if you’re selfish and mean. For a short time and against a specific set of opponents, some selfish organisms may come out ahead. But selfishness isn’t evolutionarily sustainable," Christoph Adami, a professor at Michigan State University and the lead author of the paper, said at the time.