550-million-year-old fossil reveals the evolutionary origin of being right- or left-handed

The habit of using the right or left hand is not unique to humans; today, a tendency to prefer one side of the body is seen in many creatures, from kangaroos to chimpanzees. Scientists have discovered that the history of these behavioral traits dates back much further than previously thought, to 550 million years ago. This finding was obtained by examining fossils of the Spriggina floundersi species, one of the first known animals to have a head and bilateral symmetry.

In the study published in the journal Scientific Reports, more than 100 fossils found in the Güney region of Australia were examined in detail. It was determined that this tiny creature, which lived on the seafloor during the Ediyakaran period and had no arms or legs, showed a tendency to turn to the right when bending its body. Confirming that this situation was not caused by ocean currents or the fossilization process, researchers accepted the phenomenon as a behavioral bias.

This discovery indicates that even in the early stages of the evolution of bilaterally symmetrical organisms, the nervous system might have possessed a certain directional organization. It is thought that the creature needed muscles and a primitive nervous system to coordinate its different movements. However, scientists have not yet been able to fully determine why this side preference emerged or what function it served.