September 5, 2013
from PreventDisease Website
War is the epitome of a selfish and power hungry mentality that destroys the true spirit of humanity.
University of Pennsylvania biologists offer a mathematically based explanation for why cooperation, forgiveness, altruism and generosity succeed in the long-term benefit of populations where selfish and disharmonious intentions fail.
Their work builds upon the seminal
findings of economist John Nash, who advanced the field
of game theory in the 1950s, as well as those of computational
biologist William Press and physicist-mathematician
Freeman Dyson, who last year identified a new class of
strategies for succeeding in the classical game theory match-up
known as the "Prisoner's Dilemma."
Postdoctoral researcher Alexander J. Stewart and associate professor Joshua B. Plotkin, both of Penn's Department of Biology in the School of Arts and Sciences, examined the outcome of the Prisoner's Dilemma as played repeatedly by a large, evolving population of players.
While other researchers have previously suggested that cooperative strategies can be successful in such a scenario, Stewart and Plotkin offer mathematical proof that the only strategies that succeed in the long term are generous ones.
They report their findings (From
Extortion to Generosity, Evolution in the Iterated Prisonerís
Dilemma) in this week's issue in
The Prisoner's Dilemma is a way of studying how individuals choose whether or not to cooperate.
In the game, if both players cooperate, they both receive a payoff. If one cooperates and the other does not, the cooperating player receives the smallest possible payoff, and the defecting player the largest. If both players do not cooperate, they receive a payoff, but it is less than what they would gain if both had cooperated.
In other words, it pays to cooperate, but it can pay even more to be selfish.
In the Iterated Prisoner's Dilemma, two players repeatedly face off against one another and can employ different strategies to beat their opponent.
In 2012, Press and Dyson "shocked the world of game theory," Plotkin said, 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 related linearly to the other.
What's more, they focused on a subset of zero determinant approaches they deemed to be extortion strategies. If a player employed an extortion strategy against an unwitting opponent, that player could force the opponent into receiving a lower score or payoff.
Stewart and Plotkin became intrigued with this finding, and last year wrote a commentary (Extortion and cooperation in the Prisonerís Dilemma) in PNAS about the Press and Dyson work.
They began to explore a different approach to the Prisoner's Dilemma. Instead of a head-to-head competition, they envisioned a population of players matching up against one another, as might occur in a human or animal society in nature. The most successful players would get to "reproduce" more, passing on their strategies to the next generation of players.
It quickly became clear to the Penn biologists that extortion strategies wouldn't do well if played within a large, evolving population because an extortion strategy doesn't succeed if played against itself.
In generous strategies, which are essentially the opposite of extortion strategies, players tend to cooperate with their opponents, but, if they don't, they suffer more than their opponents do over the long term.
"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.
Stewart noticed the first of these generous approaches among the zero determinant strategies that Press and Dyson had defined.
After simulating how some generous strategies would fare in an evolving population, he and Plotkin crafted a mathematical proof showing that, not only can generous strategies succeed in the evolutionary version of the Prisoner's Dilemma, in fact these are the only approaches that resist defectors over the long term.
The discovery, while abstract, helps
explain the presence of generosity in nature, an inclination
that can sometimes seem counter to the Darwinian notion of
survival of the fittest.
In these situations, they are just motivated to get around all these negative things and once the penalties are lifted for not cooperating, people are often no longer inspired to do so.
Cooperative Experience is Key
A first analysis contradicts what many researchers have held based on theoretical studies.
Ruling out that network
organization influences in the cooperation of people, and having
discovered that what is important is reciprocity, that is,
cooperating according to cooperation received, will radically
change the focus of a significant number of researchers who are
developing theories on the emergence of cooperation among