The ties of kinship have long been recognized as promoting the spirit of giving without an expectation of receiving in return, yet some creatures lend a helping hand to those with whom they share no blood bonds, the study authors from the University of Michigan in Ann Arbor pointed out in the British journal Nature.
Such generosity among unrelated individuals appears tied to perceptions of some similarity -- be it in language or group affiliation or some other arbitrary trait or "tag" -- between the one in need and the one offering assistance, scientists told United Press International.
"The significance of our findings is that they demonstrate a new approach to explaining the emergence and maintenance of cooperation in animals and humans," said study co-author Robert Axelrod, professor at the Gerald R. Ford School of Public Policy.
"There are two well-established explanations for why one animal or human would cooperate with another, even at a cost to itself. One possibility is kinship, as in a mother helping her child. The second explanation is that the prospect for future interactions allows cooperation to be built on the basis of reciprocity, as in a strategy of tit for tat. A third explanation that applies to people is cooperation based on the need to maintain a good reputation, lest others not cooperate with you," Axelrod told UPI.
"We show that even if none of these explanations apply, cooperation can be sustained in yet another way. We find that if individuals are generous to others who are very similar to themselves, this too can sustain cooperation. And this works even if the basis for judging similarity is a completely arbitrary characteristic."
Thus, any observable trait -- a marking, a smell, a display -- can lead to acts of kindness even toward total strangers, scientists said. The selection mechanism is either "classical," if the traits-in-common are inherited genetically, such as hair color, or social, if they are inherited culturally, such as a dress code, investigators said.
Just how broadly one views the cooperation-enhancing commonality -- be it membership in a small club or in the entire human race -- bespeaks one's level of tolerance, which can fluctuate over time.
As one example, Afghan tribes that once viewed themselves as mortal enemies due to individual differences united when attacked by Russian forces, the invaders now taking on the antagonistic "outsiders" role, investigators told UPI.
"It is possible for cooperation to evolve where people might be surprised to see it; it could evolve on the simple basis of helping people who are like you," said study co-author Rick Riolo, associate research scientist at the Center for the Study of Complex Systems.
"Afghani groups under some conditions are all fighting each other, thinking the tribe over the hills is not like me, but when the Russians invade, now all of a sudden, they decide we are all the same, the Russians are not like us so let's band together," Riolo said in a telephone interview. "The key question is what you decide to call yourself and who you decide not to call what you call yourself."
"These oscillations of tolerance levels are striking and bring to mind many historical instances," said Karl Sigmund of the University of Vienna and the International Institute for Applied Systems Analysis in Laxenburg, Austria, and Martin Nowak at the Institute for Advanced Study in Princeton, N.J., who analyzed the findings in an accompanying commentary. "We are witnessing a wave of social and religious intolerance right now."
The findings are based on a computer simulation that takes into account a fundamental principal of evolution: that individuals who do well in one generation are more likely to have offspring in the next, Axelrod said.
"The simulation is based on a donation game in which one agent can make a donation to another at a slight cost to itself. In this game, there is little chance of meeting the same partner again, so reciprocity is not possible. While the spread of successful strategies can be regarded as being due to evolution over many generations, it can also be due to imitation within a single generation," he explained.
"In our model, an agent's 'tolerance' indicates just how similar another agent has to be to merit making a donation to it. We find that tolerance fluctuates over time. The average level of cooperation also fluctuates, but after it falls (due to a decrease in tolerance), it is soon restored as the average level of tolerance increases."
The authors' method has "obvious link to reality," Sigmund and Nowak said. "School ties, club memberships, tribal customs or religious creeds are all tags that induce cooperation."
Since some traits are easy to falsify, they could give rise to exploitation by unscrupulous outsiders driven by self-interest, they said. The cuckoo, which lays its eggs in the nests of other birds in hopes the unsuspecting mother will raise the foundlings as her own, provides an example.
"Language, on the other hand, could be a reliable tag that is hard to fake; hiding one's accent in a foreign language is nearly impossible," Sigmund and Nowak said.
"Tags are initially chosen at random, as are tolerances, but both are heritable and subject to mutation," the study authors said.
A regional accent, a hat of a particular color, a secret handshake can bespeak a stranger's similarity. Thus, cooperation can exist in big cities, or even globally, where repeated interactions between individuals is rare.
By promoting cooperation, tags can serve a useful purpose.
"Indeed, to find out how much one has in common is one of the first delights of falling in love and contemplating a lifelong partnership," Sigmund and Nowak noted.
On the other hand, traits-based judgments carry the danger of leading to the kind of stereotyping, segregation, discrimination and intolerance that has captured recent headlines.
"We know that discrimination is needed to sustain cooperation in the face of exploiters," Sigmund and Nowak concluded. "But tag-based intolerance could turn discrimination away from the 'bad guys' and raise senseless antagonism."
Applications of the models cannot be as straightforward as engineering a bridge, the study authors agreed.
"When working with complex systems, there are no simple answers," Riolo told UPI. "These models at least give you ideas of what kinds of things might make a difference."