ls 'survival of the fittest' finished? Scientists 'prove' that generosity Researchers applied Prisoner's Dilemma theory to populations Dilemma involves choosing to save yourself or help another person When played with two people, being selfish gives the best result Yet being selfish when in a large group eventually breeds selfish behaviour and the group as a whole loses out on initial benefits Study concludes that this 'proves' why generosity evolved in nature header It's long been thought that humans evolved by looking out for themselves and making selfish decisions, yet it appears this evolution theory may have taken a turn as scientists discover being generous and working as a team is now the only way we can survive. Being selfish in the short term may garner the best immediate results, but selfish people will end up being less successful over time compared to their more generous counterparts, claims a new study. By applying the Prisoner's Dilemma theory - usually played with two people in which they are asked to incriminate each other to escape punishment - to populations, researchers from Pennsylvania found that cooperation evolved because being generous breeds success for all. This is because when the dilemma is played in pairs, being selfish guarantees the person making the decision the best possible outcome, yet, over time, being selfish to someone will eventually cause that person to be selfish in return meaning the initial successes are undone and no one wins. Researchers from Pennsylvania claim that teamwork, seen in insects such as the leafcutter ants pictured, evolved because being generous makes groups as a whole more successful. This only works when generous people also forgive selfish people and don't seek revenge Researchers used the Prisoner's Dilemma game to study cooperation where two people who have committed a crime are arrested and each are offered a deal by police. The premise is, grass on your friend and go free while the friend spends six months in jail. If both prisoners grass, they both get three months in jail. If they both stay silent, they both get one month in jail for a lesser offence. If the two prisoners get a chance to talk to each other, they can establish trust and are usually more likely to cooperate because then both of them only spend one month in jail. But if they're not allowed to talk, the best strategy is to grass because it guarantees you don't get the longer jail term. The game allows scientists to study a basic question faced by individuals competing for limited resources - do I act selfishly or do I cooperate? They add that when everyone cooperates and is generous, that generosity spreads and everyone succeeds eventually, even if they have to make sacrifices. The study continues that this also needs to be coupled with forgiveness, meaning if someone has been wronged they should not seek revenge but instead show generosity in return. Researchers Alexander J. Stewart and Joshua B. Plotkin from Pennsylvania's Department of Biology in the School of Arts and Sciences, examined the outcome of the Prisoner's Dilemma when played repeatedly by a large, evolving group of players. While other researchers have previously suggested that being cooperative can be successful, Stewart and Plotkin offer 'mathematical proof' that the only strategies that succeed in the long term are generous ones. 'Ever since Darwin,' said Plotkin, 'Biologists have been puzzled about why there is so much apparent cooperation, and even flat-out generosity and altruism, in nature. The literature on game theory has worked to explain why generosity arises. Our paper provides such an explanation for why we see so much generosity in front of us. According to Plotkin, in 2012, Press and Dyson 'shocked the world of game theory' by identifying a group of strategies for playing this version of the game. They called this class of approaches 'zero determinant' strategies because the score of one player is directly related to the other. They also focused on a range of zero determinant approaches they called extortion strategies. If a player taking part in a so-called extortion strategy - in which they extort the situation for their personal game - against an unwitting opponent, that player could force the opponent into getting a lower score, or losing out. Being selfish in the short term guarantees the best possible immediate outcome, yet, over time, being selfish to someone will eventually cause that person to be selfish in return meaning the initial successes are undone and no-one wins. This then affects the overall success of a group Instead of a head-to-head competition, Stewart and Plotkin applied this to a population of people playing against one another, to mimic what might happen in a human or animal society in nature. In their version of the game, the most successful players would get to have more offspring, therefore passing on their strategies to the next generation of players. During research, Stewart and Plotkin found that the extortion strategies wouldn't do well if played within a large, evolving population because an extortion strategy doesn't succeed when played against itself. Study used the Prisoner's Dilemma in which a person is offered the chance to walk away free if they incriminate someone else 'The fact that there are extortion strategies immediately suggests that, at the other end of the scale, there might also be generous strategies,' said Stewart. 'You might think being generous would be a stupid thing to do, and it is if there are only two players in the game, but, if there are many players and they all play generously, they all benefit from each other's generosity. 'In generous strategies players tend to cooperate with their opponents more, but, if they don't, they suffer more than their opponents do over the long term. The continued that 'forgiveness' is also a feature of these strategies - a player who encounters a defector may punish the defector a bit but after a time may cooperate with the defector again. After simulating how some generous strategies would play out in an evolving population, he and Plotkin crafted a mathematical formula proving that, not only can generous strategies work best in the population version of the Prisoner's Dilemma, these are the only approaches that resist defectors over the long term. 'Our paper shows that no selfish strategies will succeed in evolution,' Plotkin said. The only strategies that are evolutionarily robust are generous ones. The discovery, while abstract, helps explain the presence of generosity in nature, an inclination that can sometimes seem to go against the Darwinian notion of survival of the fittest. 'When people act generously they feel it is almost instinctual, and indeed a large literature in evolutionary psychology shows that people derive happiness from being generous,' Plotkin said. 'It's not just in humans. Of course social insects behave this way, but even bacteria and viruses share gene products and behave in ways that can't be described as anything but generous.' 'We find that in evolution, a population that encourages cooperation does well,' Stewart said. To maintain cooperation over the long term, it is best to be generous. The findings were reported in the PNAS journal.