# Competition-driven evolution of organismal complexity

## TL;DR

This paper presents a model explaining how ecological pressures and competition drive non-uniform increases in organismal complexity through threshold effects, leading to punctuated evolutionary patterns.

## Contribution

It introduces a quantitative competition model showing how diversification and ecological pressures cause stepwise increases in phenotypic complexity.

## Key findings

- Sequential complexity increases driven by diversification.
- Ecological pressure thresholds trigger phenotypic innovations.
- Model reproduces punctuated evolution patterns.

## Abstract

Non-uniform rates of morphological evolution and evolutionary increases in organismal complexity, captured in metaphors like "adaptive zones", "punctuated equilibrium" and "blunderbuss patterns", require more elaborate explanations than a simple gradual accumulation of mutations. Here we argue that non-uniform evolutionary increases in phenotypic complexity can be caused by a threshold-like response to growing ecological pressures resulting from evolutionary diversification at a given level of complexity. Acquisition of a new phenotypic feature allows an evolving species to escape this pressure but can typically be expected to carry significant physiological costs. Therefore, the ecological pressure should exceed a certain level to make such an acquisition evolutionarily successful. We present a detailed quantitative description of this process using a microevolutionary competition model as an example. The model exhibits sequential increases in phenotypic complexity driven by diversification at existing levels of complexity and the resulting increase in competitive pressure, which can push an evolving species over the barrier of physiological costs of new phenotypic features.