Lizards have spongy hearts.  Birds and humans have advanced electrical hearts.  Just stretch out the sponge, and voila!

Advancing a theory vaguely resembling Haeckel’s biogenetic law, some Danes have deigned to relegate our hearts’ design to the reptiles.  Cold-blooded reptiles get by with spongy tissue.  Warm-blooded birds and humans, by contrast, need electrically-conducting tissue to keep the pulse in sync across the blood-pumping organ.  Is there an evolutionary connection somewhere?  If so, it’s been a mystery for a long time:

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.

According to Science Daily, researchers have found “Our Inner Reptilian Hearts.”  They looked into the hearts of lizards, frogs and fish, hunting for a gene that forms conductive properties.  They “discovered a common molecular structure that’s hidden by the anatomical differences,” they claimed.

Buried within the article is the Darwinian connection: “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 in adult birds and mammals.”  This is cause for celebration:

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….

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