The genetic building blocks behind the human heart's subtle control system have been identified by researchers.
An elaborate system of leads spreads across our hearts. These leads - the heart's electrical system - control our pulse and coordinate contraction of the heart chambers.
While the structure of the human heart has been known for a long time, the evolutionary origin of our conduction system has nevertheless remained a mystery.
Researchers have finally succeeded in showing that the spongy tissue in reptile hearts is the forerunner of the complex hearts of both birds and mammals.
The new knowledge provides a deeper understanding of the complex conductive tissue of the human heart, which is of key importance in many heart conditions.
"The heart of a bird or a mammal - for example a human - pumps frequently and rapidly. This is only possible because it has electrically conductive tissue that controls the heart," Bjarke Jensen, from Department of Bioscience, Aarhus University said.
"Until now, however, we haven't been able to find conductive tissue in our common reptilian ancestors, which means we haven't been able to understand how this enormously important system emerged," he said.
Along with Danish colleagues and colleagues from the University of Amsterdam, he now reveals that the genetic building blocks for highly developed conductive tissue are actually hidden behind the thin wall in the spongy hearts of reptiles.
"We studied the hearts of cold-blooded animals like lizards, frogs and zebrafish, and we investigated the gene that determines which parts of the heart are responsible for conducting the activating current," Dr Jensen.
"By comparing adult hearts from reptiles with embryonic hearts from birds and mammals, we discovered a common molecular structure that's hidden by the anatomical differences," he added.
The study has been published in the journal PLoS ONE.