The evolutionary origins of modularity

TL;DR

This paper shows that direct selection for reducing connection costs in biological networks naturally leads to the emergence of modularity, which enhances evolvability, providing a new explanation for the evolution of modular structures.

Contribution

It demonstrates that connection cost minimization alone can drive the evolution of modularity, challenging the view that modularity arises solely from indirect selection for evolvability.

Findings

Networks with minimized connection costs are more modular.

Such networks are more adaptable to environmental changes.

Connection cost reduction leads to increased evolvability.

Abstract

A central biological question is how natural organisms are so evolvable (capable of quickly adapting to new environments). A key driver of evolvability is the widespread modularity of biological networks--their organization as functional, sparsely connected subunits--but there is no consensus regarding why modularity itself evolved. While most hypotheses assume indirect selection for evolvability, here we demonstrate that the ubiquitous, direct selection pressure to reduce the cost of connections between network nodes causes the emergence of modular networks. Experiments with selection pressures to maximize network performance and minimize connection costs yield networks that are significantly more modular and more evolvable than control experiments that only select for performance. These results will catalyze research in numerous disciplines, including neuroscience, genetics and harnessing evolution for engineering purposes.