TIGP (BIO)—Contingency and Directionality in Evolution

Abstract

The relationship between evolutionary constraint and morphological innovation remains a fundamental puzzle in biology. We propose the core-flex hypothesis predicting that traits under strong functional constraints exhibit predictable convergence, while traits under weaker or variable selection allow diversification, with core trait stability facilitating flex trait exploration through increased effective population size. Analysis of wing morphology across 17,073 Lepidoptera species supported these predictions: flight-critical traits showed strong directional evolution toward configurations with enhanced aerial maneuverability and efficient flight performance, while color patterns displayed greater evolutionary flexibility. Notably, lineages with higher morphological disparity maintained more efficient flight-related traits, and temporal analyses revealed that stabilization of core flight performance preceded flex trait diversification. These findings demonstrate how evolutionary constraint and contingency interact dynamically to generate biological diversity.

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