Generosity Leads to Evolutionary
Success, Biologists Show
With new insights into
the classical game theory match-up known as the "Prisoner's Dilemma,"
University of Pennsylvania biologists offer a mathematically based explanation
for why cooperation and generosity have evolved in nature.
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 Prisoner's Dilemma.
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 in the Proceedings of the National Academy of Sciences the
week of Sept. 2.
"Ever since
Darwin," Plotkin said, "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."
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 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.
"The fact that
there are extortion strategies immediately suggests that, at the other end of
the scale, there might also be generous strategies," Stewart said.
"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,
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.
"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 counter to 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."
Story Source:
The above story is based
on materials provided by University of Pennsylvania, via EurekAlert!, a service of
AAAS.
Note: Materials may be
edited for content and length. For further information, please contact the
source cited above.
Need to cite this story
in your essay, paper, or report? Use one of the following formats:
APA
MLA
MLA
University of
Pennsylvania (2013, September 2). Generosity leads to evolutionary success,
biologists show. ScienceDaily. Retrieved September 3, 2013, from
http://www.sciencedaily.com/releases/2013/09/130902162716.htm
