# Exploring the Causes of the Cambrian Explosion Based on the Evolution Mechanism of Genome Sequences

## TL;DR

This study explores the Cambrian explosion by analyzing genome sequence evolution in modern species, suggesting a shift in evolutionary modes may have triggered the event.

## Contribution

A novel framework for studying ancient evolutionary events using genome sequence data from modern species.

## Key findings

- The transition from TA-independent to CG-independent selection dominance may have catalyzed the Cambrian explosion.
- Estimated species origin times align with paleontological evidence for many animal and some plant groups.
- Discrepancies in certain plant groups suggest the need for further investigation.

## Abstract

This study investigated a possible cause of the Cambrian explosion—a rapid increase in biodiversity around 540–560 million years ago—by analyzing evolution modes of genome sequences in modern species. Specifically, we examined two evolutionary modes: CG- and TA-independent selection, both of which play critical roles in shaping genome sequence changes across different evolutionary levels of species. Our findings suggest that the transition from TA-independent selection dominance to CG-independent selection dominance may have acted as a catalyst for this ancient biological event. By estimating evolution timelines based on this transition, we reconstructed the origins of major species groups, which are consistent with existing paleontological evidence. This methodology offers a novel framework for studying ancient evolution events through the lens of genome sequence data from modern species.

The cause of the Cambrian explosion is one of the centuries-old puzzles. For centuries, scholars from numerous disciplines have proposed various theories based on evidence such as paleontological fossils and changes in geology and climate to try to reveal the cause of the Cambrian explosion, but no satisfactory conclusion has been reached. We explored a possible cause of the Cambrian explosion based on the evolution mechanism of genome sequences of existing species. Previous studies have found that the CG- and TA-independent selection intensities and the mutual inhibition relationship between them determine the evolution state of genome sequences. Based on the evolution mechanism of genome sequences, we analyzed the distribution of CG- and TA-independent selection intensities in animals and plants. We believed that the phase transition process from the evolution mode dominated by TA-independent selection to that dominated by CG-independent selection is an important cause of the Cambrian explosion. Consequently, we deduced the evolution time corresponding to the evolution state of genome sequences and gave the origin time of species branches. The results are largely consistent with existing paleontological evidence for animal branches and some plant branches, which verifies the rationality of our conjecture, though differences for certain plant groups require further investigation. Our study provides a novel way to reveal the cause of the Cambrian explosion and the origin time of species branches through existing genome sequences.