One of the main theories on the origin of life proposes the hypothesis according to which life evolved as cooperative networks of molecules. Explaining cooperation – and particularly, its emergence by favoring the evolution of life-bearing molecules – is therefore a key element in describing the transition from non-life to life. Two researchers from the Université de Montréal, both members of the Center for Research in Astrophysics of Quebec (CRAQ), Professor Paul Charbonneau and PhD student Alexandre Champagne-Ruel, modeled the “prisoner’s dilemma” to investigate the emergence of cooperative behaviors in a stochastic spatially extended setting and characterize the effects of inheritance and variability.
With the recent launch of the James Webb Space Telescope astronomers are closer than ever to detecting signs of life in the Universe. Directly related to this endeavour is the one pursued by scientists striving to explain how life itself has appeared on our planet, and by extension could also emerge on remote worlds. One key element which is likely to take part in this universal description of the transition from non-life to life is the concept of cooperation: if simple molecules are to be regarded as the building blocks for further complexification, then they must act in a synergistic manner towards the construction of unified systems where they each play a part cooperatively.
When we think of a natural Darwinian evolutionary system however, the first thought that crosses our mind is not necessarily cooperation. In nature, organisms are often in direct competition for resources, and life specializes in occupying and defending niches against invaders. Nevertheless, several forms of cooperation in natural contexts have evolved through history—the cells of an organism clearly do not compete, fungi take part in mutualist interactions with other lifeforms and so on, all the way up to human societies.
If explaining cooperation in higher level organisms requires that we invoke concepts such as kin selection, which already assume a certain level of biological complexity, explaining how cooperation emerges in the simplest entities is in contrast much harder. Considering the limiting case of origin of life theories which hypothesize that biology originated with small networks of auto-replicating molecules, for instance, then how can we explain cooperation between these networks? This is an important question, and one that has also motivated some recent numerical simulations by CRAQ researchers .
By evolving agents in a 2D virtual environment that could behave either cooperatively or parasitically, they gradually implemented putative elements of a prebiotic environment, starting with simple populations of agents that could or could not cooperate, and make “errors” some fraction of the time—thus defining an error rate—a reflection of the fact that the natural environments conducive to the development of life may have been subject to random disturbances. Unsurprisingly, parasitic agents often dominated—a well-known result in evolutionary game theory for this type of simulation. However, by making the error rate of agents heritable – and in doing so bringing the simulations closer to a Darwinian environment – the researchers noticed that one of the species of agents emerged much more easily from the pack, a result already striking in itself. But an even more surprising outcome resulted from the integration of a variability in those error rates – in analogy with biological variability such as mutations when organisms reproduce – for a wide range of parameter values in the model, cooperators now suddenly invaded the system in almost every simulation. Thus, as soon as they are placed in an evolutionary environment that includes heritability and variability, cooperators can thrive—even when, counterintuitively, this environment is strongly competitive and faces important external perturbations.
Those unexpected results suggest a conclusion which is twofold. First, they further substantiate the claims put forward by previous work on the origin of life that the transition from the non-living to biology is in many ways similar to the phenomenon of phase transition in physics: like the sudden transition undergone by water when it reaches the boiling point, the cooperative takeover required for life to emerge would have consisted in a dramatic event unfolding over a very short period of time. Second, they also suggest that even in the absence of complex genomes and behaviorally complex organisms, cooperation not only emerges spontaneously, but does so in a robust manner and quite easily—even in environments subject to perturbations. Moreover, if cooperation emerges so readily in nature, this might in return suggest that life could also emerge in adverse environments—as could be detected in the near future with the James Webb Telescope. The conclusions for astrobiologists could thus be summed as follow: leave no stone unturned, because natural cooperation (and thus, life!) could come up from anywhere, even from seemingly unwelcoming environments.
Département de Physique, Université de Montréal
Reference: Alexandre Champagne-Ruel and Paul Charbonneau. A Mutation Threshold for Cooperative Takeover. Life, 12(2): 254, February 2022. ISSN 2075-1729. doi: 10.3390/life12020254. https://www.mdpi.com/2075-1729/12/2/254