Why is Budi left-handed while Andi uses his right hand? What made the difference? How come it is, huh? Questions like that have long been thought of by scientists. They tried to explain the tendency to use one hand naturally compared to the other.

Various studies were conducted. For decades before, scientists assumed that this tendency originated in the human brain. Now the development of research provides other evidence that not only the brain determines this tendency.

The results of the study, published in the eLife journal, February 2017 revealed something else.

The international biopsychology team led by Ruhr University Bochum, Germany, found an important role for the spinal cord.

Also read: Is it true that Left-Handed People Tend to Atheism?

The findings of Sebastian Ocklenburg and his colleagues are quite interesting. If it is true, the tendency to use hands has been determined before the brain joins it.

In the 1980s, ultrasound scans proved that left-handedness or vice versa developed in the womb since the beginning of the 8th week of pregnancy. It was increasingly detected clearly when womb age entered the 10th week.

The results of the study were published in the journal Nature on October 4, 1990. Research shows that from week 13, the fetus tends to suck its left or right thumb.

From the study, Ocklenburg and his colleagues developed research. They look at the expression of asymmetric genes in the motor cortex and other parts of the brain, because arm and hand movements are initiated by the motor cortex.

In embryonic development, the motor cortex is not always functionally connected to the spinal cord. In fact, when early indications of hand preference arise, the spinal cord has not yet formed a relationship with the brain.

"The human fetus has shown considerable asymmetry in arm movements before the motor cortex is functionally connected to the spinal cord. So that it is more likely to assume the asymmetrical expression of the spinal gene forms the molecular basis of hand use