Emergence of self-reinforcing information bottlenecks in multilevel selection

TL;DR

This paper explores how hierarchical organization in biological systems emerges through phase transitions in information encoding, focusing on the transition to multicellularity and the role of information bottlenecks.

Contribution

It introduces a general abstract model for phase transitions in biological hierarchy formation, exemplified by the transition to multicellularity with a stochastic community model.

Findings

Transition to multicellularity involves a decrease in reproductive units.

Horizontal gene transfer reduces the fitness barrier to this transition.

The model captures key aspects like developmental evolution and unicellular bottlenecks.

Abstract

We explain how hierarchical organization of biological systems emerges naturally during evolution, through a transition in the units of individuality. We will show how these transitions are the result of competing selective forces operating at different levels of organization, each level having different units of individuality. Such a transition represents a singular point in the evolutionary process, which we will show corresponds to a phase transition in the way information is encoded, with the formation of self-reinforcing information bottlenecks. We present an abstract model for characterizing these transitions that is quite general, applicable to many different versions of such transitions. As a concrete example, we consider the transition to multicellularity. Specifically, we study a stochastic model where isolated communities of interacting individuals (e.g. cells) undergo a transition to higher-order individuality (e.g. multicellularity). This transition is indicated by the marked decrease in the number of cells utilized to generate new communities from pre-existing ones. In this sense, the community begins to reproduce as a whole via a decreasing number of cells. We show that the fitness barrier to this transition is strongly reduced by horizontal gene transfer. These features capture two of the most prominent aspects of the transition to multicellularity: the evolution of a developmental process and reproduction through a unicellular bottleneck.