New paper investigates evolutionary games and altruism

A new paper on game theory proposes a solution to a problem in evolutionary biology – how to explain the emergence of altruistic behavioural traits?

Published in the Nature journal Scientific Reports by Dr Mike Evans, lecturer in the School of Mathematics, the article discusses the surprising findings of an investigation into evolutionary game theory.

In a simulation, a simple game was played billions of times between around a quarter of a million participants. A participant (A) is given an amount of money, and must offer some non-zero portion of it to another participant (B), keeping the rest.

However – in a similar fashion to the Prisoner’s Dilemma – both participants only receive the money if B accepts the offer. If B refuses, both A and B get nothing.

Game theory, which studies the logical conclusions of playing such games optimally, suggests that the best “play” is for A to be greedy, and offer the lowest possible amount to B – and B should still accept any offer, however small, since it’s better than the alternative of getting nothing.

In this simulation, participants were each assigned two values: one corresponding to the offer they would always make to their neighbours, and the other representing the lowest offer they would accept. In order for the game to evolve, participants periodically “died” and were replaced by descendants whose offer values were increased or reduced slightly at random.

Typically, a simulation like this would confirm game theory: that the best strategy is the most self-interested one, and participants who make the greediest offers will prosper over those who act more altruistically.

However, this simulation had a few key differences. The rate of “births” was set extremely high compared to the rate of game-playing, with the result that most participants “died” without getting a chance to play. This turned out to have an extraordinary effect on the participants’ long-term strategy.

In his personal blog, PhysicsBloke, Dr Evans explains:

Under these circumstances, I find that evolution switches from favouring greed to favouring generosity. In a population with such scarce opportunities for winning resources, the average offer rises to 75%, meaning that most proposers keep less for themselves than they give away. And their generosity is indiscriminate, because agents cannot recognise close kin or choose a recipient. While 75% is the average offer, many agents give away close to 100% of their budget. It is particularly surprising that families with such a strategy are not out-competed when they meet more selfish exploiters that accept their generosity but give little back when acting as proposer.

The reasons behind this are discussed at length in the blog post and the paper, but in summary, Dr Evans proposes that when resources are scarce and pay-offs are rare, the calculus of game theory changes to favour those who are less selfish.

This idea could help to resolve a paradox that has puzzled evolutionary scientists for decades – if selfless acts are more likely to result in premature death, how have the altruistic traits and behaviours we observe in nature ever had a chance to evolve?

Dr Evans adds:

Of course, we didn't play the ultimatum game in our distant evolutionary past. But, if the game represents rare life-changing events like disasters or gluts,requiring decisive action to avoid losing out, then a similar process might be responsible for the behavioural traits that evolved as a consequence.

Further reading

Evans, RML (2018) Pay-off scarcity causes evolution of risk-aversion and extreme altruism. Scientific Reports

PhysicsBloke: Evolutionary games and altruism in the face of disaster