New Insights Reveal Human Ears Share Evolutionary Roots with Ancient Fish Gills

Recent studies have uncovered an intriguing connection between human outer ears and the gills of ancient fish. Experiments with gene editing have shown that the cartilage found in fish gills could have evolved into the outer ear structures we observe in mammals today. Researchers propose that this evolutionary shift occurred millions of years ago, implying that the origins of elastic cartilage in human ears may trace back to primordial marine invertebrates like horseshoe crabs.

Research Unveils Evolutionary Connection

A study published in Nature, led by Gage Crump, a Professor of Stem Cell Biology and Regenerative Medicine at the University of Southern California, aimed to explore the enigmatic origins of mammalian outer ears. Elastic cartilage, the main material in human outer ears, is specific to mammals and offers more flexibility compared to other cartilage types present in the human body. The study revealed that this cartilage type is also found in the gills of current bony fish species, including zebrafish and Atlantic salmon.

Gene-Editing Trials Shed Light

As reported by Live Science, researchers conducted experiments by inserting human genetic enhancers related to outer ear formation into zebrafish genomes. This manipulation activated functions in the fish gills, indicating a genetic relationship between these anatomical structures. Conversely, transferring zebrafish enhancers to mouse genomes resulted in activity in the mice’s outer ears, further solidifying the link between fish gills and mammalian ears.

Connections to Ancient Marine Life

The research team also demonstrated that reptiles and amphibians possess inherited gill-associated structures from fish. Observations from green anole lizards suggested that elastic cartilage began migrating from gills to ear canals by the time reptiles emerged around 315 million years ago. Moreover, a gene-regulating element found in horseshoe crabs, which date back 400 million years, activated functions in fish gills, hinting at even older evolutionary connections.

According to the researchers, these results emphasize the evolutionary repurposing of ancestral gill structures in the formation of mammalian ears throughout history.