Left-handedness and right-are formed through the spinal cord, before its connection with the head.
This hypothesis was put forward by scientists from Ruhr University in Germany, published the results of their work in the journal eLife.
During the experiment scientists observed for embryos in the womb. The results showed that at 13 weeks they prefer to suck the left or right thumb. Hand movements occur thanks to the work of the motor cortex of the brain, which sends signals to the spinal cord. But at this stage of development the link between cortex and spinal cord has not formed yet.
According to these data, the researchers came to the conclusion that the predominance of one of the arms does not depend on the brain and spinal cord.
In addition, the researchers observed the gene expression in five fetuses at 8-12 weeks of development. They found a difference in the number of genes that is expressed on the right and left parts of the spinal cord. This difference was notable in those areas responsible for movement of the arms and legs.
The reason for this asymmetry researchers have described the influence of environment in their opinion, it leads to greater activity either side of the spinal cord.