The loss of physical traits—such as limbs in snakes or eyes in cavefish—is a common feature of evolution, yet the genetic mechanisms enabling such changes remain incompletely understood. In a study published in Science Advances, researchers at the Technion–Israel Institute of Technology reveal how organisms can undergo significant morphological changes despite possessing highly stable and redundant genetic regulatory systems.

Led by Dr. Ella Preger-Ben Noon and Ph.D. candidate Areej Said-Ahmad from the Ruth and Bruce Rappaport Faculty of Medicine, the team investigated how gene expression evolves when controlled by multiple enhancers—DNA regulatory elements that ensure precise and robust activation of genes during development. These enhancers often function redundantly, buffering against mutations and maintaining stable gene activity.

Focusing on the fruit fly Drosophila sechellia, which has evolutionarily lost larval hair-like structures (trichomes), the researchers examined regulation of the shavenbaby gene, known to control this trait. Surprisingly, they found that four separate enhancers governing this gene independently lost their activity over time, each through a different molecular mechanism.

The study identified several distinct pathways leading to reduced enhancer function, including deletion of critical DNA segments, loss and gain of transcription factor binding sites, emergence of silencing elements, and activation of previously hidden repressive effects. Despite acting within the same regulatory system, these diverse changes all converged on the same evolutionary outcome: loss of gene expression and, consequently, loss of the physical trait.

These findings resolve the “stability paradox” by showing that regulatory redundancy, while promoting robustness, also creates multiple opportunities for evolutionary change. The work highlights how complex genetic systems can remain stable overall while still allowing flexibility in form and structure, offering new insights into the molecular basis of evolutionary diversity.