A new study sheds light on how fins may have evolved into limbs.

It is known that a fish-like common ancestor evolved into land-based vertebrates and four-footed creatures known as tetrapods. Amphibians, sauropsids and mammals are called tetrapods.

The new study led by a team of researchers from Spain shows evidence of how legs and hands evolved from fins by gaining new DNA elements that activate particular genes.

For their study, researcher José Luis Gómez-Skarmeta and Fernando Casares of the CSIC-Universidad Pablo de Olavide-Junta de Andalucía in Spain used an extra copy of the gene Hoxd13 at the tip of a zebrafish embryo's fin. Hoxd13 holds a significant role in differentiating body parts of the zebrafish.

Immediately after the Hoxd13 gene was introduced, the research team noticed the development of cartilage tissue and reduction of fin tissue.

Researchers wanted to find out if the control elements of Hoxd13 might have activated the gene expression that played a role in the evolution of limbs from fins in the past. They used a DNA control element from a mouse, as fish lack the element.

They found that the control elements drove the Hoxd13 gene expression in the fish and helped in forming limbs instead of fins.

"We found that in the zebrafish, the mouse Hoxd13 control element was capable of driving gene expression in the distal fin rudiment. This result indicates that molecular machinery capable of activating this control element was also present in the last common ancestor of finned and legged animals and is proven by its remnants in zebrafish," Dr. Casares said in a statement.

The findings of the study are published in the journal Developmental Cell.