Quantifying the Emergence of Selection Prior to Biological Evolution

TL;DR

This paper introduces a quantitative framework to measure selection in prebiotic chemical systems, demonstrating how directed exploration differs from undirected reactions through the Assembly Theory, thus providing a new way to detect chemical evolution.

Contribution

It presents an experimental method based on Assembly Theory to quantify selection in chemical systems before life, distinguishing directed from undirected chemical exploration.

Findings

Undirected reactions explore sequence space almost uniformly.

Reactions influenced by evolved proteases show lower exploration ratios.

The exploration ratio and assembly A reliably distinguish directed from undirected exploration.

Abstract

Selection is central to biological evolution, yet there has been no general experimental framework for quantifying selection in chemical systems before life. Here we demonstrate that selection in a prebiological chemical system can be directly quantified. Assembly Theory predicts that selection corresponds to a transition from undirected to directed exploration of chemical possibility space, measurable through the amount of Assembly, A, which integrates molecular assembly index with observed copy number. By analysing peptide ensembles produced under diverse polymerisation conditions, we show that undirected reactions explore sequence space almost uniformly, yielding exploration ratios of 0.85-0.95, whereas reactions influenced by evolved proteases generate markedly lower ratios (0.51-0.75) and elevated A, consistent with selective reinforcement of specific assembly pathways. Across multiple environments and amino-acid combinations, the exploration ratio and ensemble assembly A robustly distinguish directed from undirected exploration, establishing a general, experimentally tractable metric for detecting and measuring selection in chemical evolution.