Researchers from the Netherlands, United Kingdom and China sought genes that played a part in the left-right differences of the nervous system, during the four-to-eight weeks post-fertilization.
At eight weeks, embryos often favor their right arms over their left arms. Signals travel from the spinal cord as opposed from the brain, at this stage.
Biological Psychiatry published the study.
Here are five insights:
1. Researchers found the spinal cord's left side matures faster than the cord's right side, due to certain genes achieving a "more advanced profile of activity on the left side than the right."
2. In contrast, the hindbrain experiences faster growth on the right side. The researchers note this is because nerve fibers cross over from one side at the hindbrain and spinal cord boundary.
3. The researchers are not sure how the spinal cord's left-right genetic difference results in right-handedness, however.
4. They postulate that this spinal cord genetic process may trigger the brain's asymmetries developed later, like the dominance of the brain's left hemisphere for language in adults.
5. Since 85 percent of people express right-handedness, it represents the standard. Thus, genetic and environmental factors may cause left-handedness and two-handedness.