Human fetal hearts

The studies show that it is simply the spongy inner tissue in the fetal heart that gets stretched out to become a fine network of conductive tissue inadult birds and mammals. And this knowledge can be put to use in the
future. "Our knowledge about the reptilian heart and the evolutionary background to our conductive tissue can provide us with a better understanding
of how the heart works in the early months of fetal life in humans, when many women miscarry, and where heart disorders are thought to be the leading cause of spontaneous abortion," says Professor Tobias Wang.

Reptiles are cold-blooded animals and therefore have the same temperature as their surroundings. Their spongy hearts are efficient enough to maintain their low metabolism.

Birds and mammals -- including humans -- have independently of each other developed a high body temperature (warm-bloodedness) and spend enormous amounts of energy maintaining it. Their pulse has to increase to pump all the blood needed for high metabolism. This means they require efficient conductive tissue in the heart.