spaceSpace and Physics

Chance Events Make Altruism Inevitable


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

Brewer with product
Brewer's yeast has to cooperate to break down complex sugars, but it is only when it “works" with humans that it produces beer. Kzenon/Shutterstock

Random events help explain the old conundrum of why altruism is so common in nature, including among humans, a new study claims.

Under a crude interpretation of evolution, helping others makes no sense unless it benefits close relatives. Yet people risk their lives for strangers or even to rescue a puppy. The question of why troubles biologists and philosophers.


In Proceedings of the National Academy of Sciences, a team of researchers present a mathematical model that suggests chance events have programmed most of us towards pulling our weight.

The authors note that in most environments, there are “cooperators” who act to benefit others and “cheaters” who are only out for themselves. Despite the saying, cheats are expected to do better for themselves and thus pass on their genes. If cheating is hereditary, this should lead to more cheaters.

In the complex world of humans, where most people cooperate some of the time and cheat at others, this is hard to model, so the authors turned to Brewer's yeast for simplicity. Yeast produces the enzyme invertase, which breaks down complex sugars. A yeast that releases invertase gains a benefit, but non-producing yeasts gets to gobble up the simpler sugars, without expending the energy that goes into invertase production, an exemplar of cheating. Yet they have not taken over.

Dr Tim Rogers of the University of Bath said in a statement: "Scientists have been puzzled by this for a long time. One dominant theory was that we act more favorably towards genetic relatives than strangers, summed up by J. S. Haldane's famous claim that he would jump into a river to save two brothers or eight cousins.” Yet clearly this is not the whole answer. It is unlikely Haldane would have checked a family tree if he saw a child drowning, and certainly other species don't.


"What we are lacking is an explanation of how these behaviors could have evolved in organisms as basic as yeast," Rogers said. "Our research proposes a simple answer – it turns out that cooperation is favored by chance."

The problem, Rogers' work suggests, is that people were focusing on the individual, not the whole population and making what the authors call; "the unrealistic assumptions of fixed population size". Yeast cooperators make more food available in total, leading to a larger total population size. Rogers' model showed that random fluctuations can lead to an increase in cheaters, in which case the available food supply will not sustain the whole population, causing a crash. On the other hand, a fluctuation that produced more cooperators would lead to more food and a larger population.

Such random changes ensure populations with more cooperators thrive, increasing the chances that those present, the majority of which are cooperators, will migrate to other locations and dominate populations..

First author Dr George Constable of Princeton compared the situation to flipping a coin where heads gives a cooperator twice as much as it loses when the coin lands tails. “Although the odds winning or losing are the same, winning is more good than losing is bad," Constable said. "Random fluctuations in cheat numbers are exploited by the cooperators, who benefit more then they lose out."


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