Inverse relationship between genetic diversity and epigenetic complexity

Shi Huang

doi:10.1038/npre.2008.1751.1

Abstract

AbstractEarly studies of molecular evolution revealed a correlation between genetic distance and time of species divergence. This observation provoked the molecular clock hypothesis and in turn the ‘Neutral Theory’, which however remains an incomplete explanation since it predicts a constant mutation rate per generation whereas empirical evidence suggests a constant rate per year. Data inconsistent with the molecular clock hypothesis have steadily accumulated in recent years that show no correlation between genetic distance and time of divergence. It has therefore become a challenge to find a testable idea that can reconcile the seemingly conflicting data sets. Here, an inverse relationship between genetic diversity and epigenetic complexity was deduced from a simple intuition in building complex systems. Genetic diversity, i.e., genetic distance or dissimilarity in DNA or protein sequences between individuals or species, is restricted by the complexity of epigenetic programs. This inverse relationship logically deduces the maximum genetic diversity hypothesis, which suggests that macroevolution from simple to complex organisms involves a punctuational increase in epigenetic complexity that in turn causes a punctuational loss in genetic diversity. The hypothesis explains a diverse set of biological phenomena, including both for and against the correlation between genetic distance and time of divergence.

Highlights

It is remarkable that the human mind is able to comprehend nature
Intuition may directly impact the science of biology without going through the bridge of mathematics, or chemistry, or physics, such an intuition-based law of biology has yet to be uncovered
The maximum genetic diversity (MGD) hypothesis suggests that the rates of change in genetic distance for macroevolution are determined by epigenetic complexity

Summary

Introduction

It is remarkable that the human mind is able to comprehend nature. The scientific understanding of nature is largely based on mathematics. To compensate for the loss in the range of genetic diversity, complex organisms use different epigenetic programming of the same gene set, in addition to mutation, to adapt to environments and to evolve new phenotypes. The notion that genetic distance is roughly a function of time and mutation rates only applies to diverging organisms of similar complexity over short time scales prior to reaching the maximum cap.

Results

Conclusion