# The Constructive Neutral Evolution of Behaviour

## TL;DR

The paper argues that nonfunctional behavioral complexity can evolve through a process called constructive neutral evolution, which is already recognized in molecular biology but overlooked in behavioral ecology.

## Contribution

The paper introduces the idea that constructive neutral evolution applies to behavior, not just molecules, and provides a framework for testing this hypothesis.

## Key findings

- Behavioral complexity can increase without functional improvement through constructive neutral evolution.
- Behaviors' genetic and functional properties make them susceptible to CNE.
- Indirect evidence supports the occurrence of behavioral CNE, and the paper proposes ways to test it directly.

## Abstract

There is an unrecognised disagreement between those studying molecular evolution and those studying behavioural evolution. Only natural selection is ordinarily thought to systematically increase behavioural complexity, but molecular biologists are increasingly recognising a second driver of complexity—constructive neutral evolution (CNE). CNE occurs when a system contains components that buffer the effects of otherwise‐deleterious mutations, allowing such mutations to spread. This increases the complexity of the system due to the dependency that now exists between the buffering component and the mutated component. A probabilistic ‘ratchet’ means this process is more likely to repeat itself than reverse, and hence complexity increases without necessarily any gain in function. Here, we argue that CNE operates not only at the molecular level, but also affects whole organism behaviour. We suggest that behaviour's polygenic architecture, flexibility, and ability to mitigate the impact of otherwise‐deleterious mutations mean that behaviour is particularly likely to evolve via CNE. We summarise the evidence that supports this hypothesis as well as suggesting how it could be tested further. We conclude that CNE must be considered alongside selective explanations for increases in behavioural complexity.

We explain how constructive neutral evolution (CNE) can lead to the evolution of nonfunctional behavioural complexity, highlighting a mechanism that is unknown to behavioural ecologists despite being frequently considered by molecular biologists. We summarise indirect evidence that suggests behavioural CNE has occurred and outline how the hypothesis can be tested more directly.