Life may not exist at the 鈥渆dge of chaos鈥� after all. The long-standing belief has been challenged by computer simulations of dozens of processes within cells.
A hallmark of chaotic systems is that a small disturbance can lead to an outsized effect. The famous butterfly effect offers a classic example, where a flap of an insect鈥檚 wings is proposed to cause a storm many kilometres away. Since the late 1980s, researchers have believed that life has evolved to exist right at the edge of this kind of chaos in its search for the middle ground between being adaptable to the environment and remaining stable enough to survive.
鈥淭he idea of the edge of chaos is that cells want to have as much sensitivity as they possibly can, without going into this chaotic regime where the tiniest breeze makes the cell fall apart,鈥� says at Binghamton University in New York. 鈥淔or a long time, people have thought that this edge of chaos phenomenon happens not only at the level of whole cells or organisms, but also if you look at the specific jobs that the cell has to do.鈥�
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The idea has been tested by studying mathematical models that break down cellular processes, like gene regulation, into networks of interactions. But those models haven鈥檛 always been validated by experiments involving living cells. So, Rozum and his colleagues set out to test the edge of chaos idea using dozens of models that are rigorously rooted in biological studies.
They chose 72 experiment-based models representing processes ranging from cell death to gene regulation in the bacterium Escherichia coli. The models came from the , which collects the work of many independent researchers.
Rozum and his colleagues then ran a computer simulation in which each model was perturbed 鈥� for instance, by slightly mistiming the interaction between two proteins or two genes. They wanted to see whether the model would react strongly, implying life is on the edge of chaos, or less so, which would suggest life is not as close to chaotic as generally thought.
The research was computationally challenging because the researchers wanted to run the simulations over a long enough time to capture the full response to the perturbation and not just a transient reaction. Using graphic processing units (GPUs) like those used for video games helped them simulate and analyse a large and statistically meaningful number of data points, says Rozum.
Across the models, their conclusion was the same: life is remarkably good at recovering from perturbations, which wouldn鈥檛 be the case if it existed at the edge of chaos.
at Portland State University in Oregon says the new computational method is an exciting tool and the conclusions it led to complicate the discussion of what exactly the edge of chaos is.
Though models rigorously rooted in laboratory studies haven鈥檛 been so extensively studied before, the new study may still include too few of them for generalising its conclusions to all life, he says. There is no question that living organisms exist at 鈥渟weet spots鈥� somewhere between order and chaos, but it remains an open question how similar those spots are across all life forms and all of life鈥檚 processes, says Teuscher.
For Rozum, the new study is not the nail in the coffin for the edge of chaos hypothesis, but an incentive to characterise it better. While he and his colleagues showed that many cellular processes themselves are far from the edge of chaos, it could still be true that when they all combine the cell as a whole moves closer to chaos, he says. The researchers plan on studying that idea next, using even more complex computer simulations.
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