Colloquium: Criticality and dynamical scaling in living systems

TL;DR

This paper discusses the hypothesis that living systems operate near critical points of phase transitions, which may confer optimal adaptability, computational capacity, and sensitivity, supported by emerging empirical evidence across various biological systems.

Contribution

It reviews the concept of criticality in living systems, highlighting recent empirical findings and discussing its potential as a unifying organizing principle in biology.

Findings

Evidence of criticality in brain activity and gene expression

Examples of criticality in animal groups like bird flocks and insect colonies

Support for the hypothesis that biological systems operate near critical points

Abstract

A celebrated and controversial hypothesis conjectures that some biological systems --parts, aspects, or groups of them-- may extract important functional benefits from operating at the edge of instability, halfway between order and disorder, i.e. in the vicinity of the critical point of a phase transition. Criticality has been argued to provide biological systems with an optimal balance between robustness against perturbations and flexibility to adapt to changing conditions, as well as to confer on them optimal computational capabilities, huge dynamical repertoires, unparalleled sensitivity to stimuli, etc. Criticality, with its concomitant scale invariance, can be conjectured to emerge in living systems as the result of adaptive and evolutionary processes that, for reasons to be fully elucidated, select for it as a template upon which higher layers of complexity can rest. This hypothesis is very suggestive as it proposes that criticality could constitute a general and common organizing strategy in biology stemming from the physics of phase transitions. However, despite its thrilling implications, this is still in its embryonic state as a well-founded theory and, as such, it has elicited some healthy skepticism. From the experimental side, the advent of high-throughput technologies has created new prospects in the exploration of biological systems, and empirical evidence in favor of criticality has proliferated, with examples ranging from endogenous brain activity and gene-expression patterns, to flocks of birds and insect-colony foraging, to name but a few...