Lungs and limbs have been thought of as key innovations that came with the vertebrate transition from water to land. But in fact, the genetic basis of air-breathing and limb movement was already established in our fish ancestor 50 million years earlier, according to a recent genome mapping of primitive fish. The new study changes our understanding of a key milestone in our own evolutionary history.

There is nothing new about humans and all other vertebrates having evolved from fish. The conventional understanding has been that certain fish shimmied landwards roughly 370 million years ago as primitive, lizard-like animals known as tetrapods. According to this understanding, our fish ancestors came out from water to land by converting their fins to limbs and breathing under water to air-breathing.

However, limbs and lungs are not innovations that appeared as recent as once believed. Our common fish ancestor that lived 50 million years before the tetrapod first came ashore already carried the genetic codes for limb-like forms and air breathing needed for landing. These genetic codes are still present in humans and a group of primitive fishes.

This has been demonstrated by recent genomic research conducted by University of Copenhagen and their partners. The new research reports that the evolution of these ancestral genetic codes might have contributed to the vertebrate water-to-land transition, which changes the traditional view of the sequence and timeline of this big evolutionary jump. The study has been published in the scientific journal Cell.

«The water-to-land transition is a major milestone in our evolutionary history. The key to understanding how this transition happened is to reveal when and how the lungs and limbs evolved. We are now able to demonstrate that the genetic basis underlying these biological functions occurred much earlier before the first animals came ashore,» stated by professor and lead author Guojie Zhang, from Villum Centre for Biodiversity Genomics, at the University of Copenhagen’s Department of Biology.

A group of ancient living fishes might hold the key to explain how the tetrapod ultimately could grow limbs and breathe on air. The group of fishes includes the bichir that lives in shallow freshwater habitats in Africa. These fishes differ from most other extant bony fishes by carrying traits that our early fish ancestors might have had over 420 million years ago. And the same traits are also present in for example humans. Through a genomic sequencing the researchers found that the genes needed for the development of lungs and limbs have already appeared in these primitive species.

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