Cooperation arises in biological systems

New research published in the journal Nature Ecology & Evolution demonstrates that negative consequences for selfish behaviour is a key factor in the evolution of cooperation across all biological scales, from genes to societies.

J. Arvid Ågren of Harvard University, in the US, Nicholas Davies of the London School of Hygiene and Tropical Medicine and Kevin R. Foster from the University of Oxford, both in the UK, have sought a deeper understanding of a central feature of all living things – the evolution of cooperation. 

The living world is a hierarchy of cooperation and, indeed, the history of evolution itself can be thought of as the story of individual replicating units renouncing their selfish, independent ways to come together to form, as the researchers term it, “new levels of biological organisation”.

Cooperation pervades all levels of the living world, they add: “genes work together in genomes, genomes in cells, cells in multicellular organisms and multicellular organisms in eusocial groups.”

Since the 1975 publication of EO Wilson’s influential text Sociobiology: the new synthesis, which brought together key insights into the evolution of altruism, most biological thinking has revolved around systems in which “kin selection” operates, such as the societies of bees and ants.

Kin selection, first formulated by Darwin but popularised and mathematically formalised by WD Hamilton and George Price in the 1960s, is an explanation for altruistic behaviour in groups of closely related individuals. Since close relatives have a proportion of the same genes, an individual’s behaviour that helps a relative at their own expense still helps propagate their own genes. 

As the great British biologist JBS Haldane once quipped, “I would lay down my life for two brothers or eight cousins”. 

Ågren and colleagues, however, are concerned that this focus on cooperation within related groups is giving us a lopsided view of cooperation more generally. In particular, they are interested in what they describe as “egalitarian cooperative systems, which are those formed between unrelated individuals”.

By looking at this oft forgotten aspect of cooperation they hope to answer the question: “what, if anything, unites the evolution of cooperative systems?”

Their answer is “enforcement”, which is “an action that evolves, at least in part, to reduce selfish behaviour within a cooperative alliance”.

There is a growing body of empirical evidence that shows the ubiquity of enforcement throughout nature. Selfish elements in genomes such as transposons, for example, which proliferate at the expense of the health of the cell are suppressed and regulated by genes evolved for this function, thus enforcing cooperative behaviour between genes.

Mitochondrial genes that over-compete with the genes of the host cell are similarly suppressed in complex cells, and in multicellular organisms mechanisms are in place to destroy selfish cell lineages, such as precancerous cells. 

In human societies, the mechanisms of enforcement are more complex and less easy to identify as purely biological due to the influence of culture, but they exist nonetheless – from punishments for transgressions to mate choice based on cooperation levels.

There are even enforcement mechanisms reducing competition and thus promoting cooperation between different species, of which the mutual relationship between figs and certain species of wasps is an example.

“Figs (Ficus spp.)” write the authors, “can abort fruits containing developing fig wasp larvae if their mothers did not pollinate the fig when depositing eggs. The fig species with the most effective sanctions (that abort most readily) have more cooperative wasps that pollinate the figs more often.”

Given this, the team developed a suite of mathematical models for a range of biological examples in order to see if enforcement would naturally arise in cooperative systems threatened by selfish behaviour. What they discovered is that “enforcement is predicted in every system, and importantly, this occurs over a wide range of parameters, which is consistent with the general importance of enforcement independently of both biological details and scale.”

The researchers are now hoping to identify “general principles for the evolution of enforcement that are applicable across many systems despite the diversity and details of each system”.

Understanding enforcement, and thus cooperative systems, is vitally important, because when enforcement fails “there are major consequences for cooperation that can even threaten species with extinction”.

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