Why some right-handed and the other left-hander? It is not in the brain
The version proposed by German scientists, refutes the connection of left-handedness with the differences between the left and right hemispheres of the brain.
Motor skills of the left and right hands are different. Most often, the dominant hand is the right, but on the planet also lives and a lot of left-handers. How many scientists yet to calculate is not possible. According to various sources, they range from 5 to 30% of humanity. Is not established and the reasons for the development of the body in a similar way.
It is known that the activity of the right hand is governed by the left hemisphere of the brain, so the predominance of the left hand may be due to its abnormal development during pregnancy. Experts offer several hypotheses: the stress of the mother, high-dose testosterone level, ultrasound and even developed evolutionary mechanisms of asymmetry. And British scientists have found a special gene for left-handers.
His version suggested the researchers from Ruhr University. While studying, which commit the embryo in the womb, they noticed that the fetus handedness appears in the earliest weeks of development. Meanwhile the brain to the 15th weeks still not associated with the spinal cord and control movements of the body. To consolidate your experts analyzed gene expression in the spinal cord at 8-12 weeks of pregnancy. They were able to identify significant differences in the left and right segments of the spinal cord, which correlated with the predominant hand of the fetus.
Why is the spinal cord the brain develops one way or the other, scientists don’t know, but they believe that cause is not a gene, and epigenetics: changing gene expression is influenced by external factors, the environment or any circumstances — as it is happening in the world of nature. For example, in domestic chickens and pigeons right eye developed much better than the left, due to the position of the eggs. Most often birds lay them in such a way that the right eye of the embryo is directed toward the translucent eggshell and the left one to the ground. In cases when the position of the eggs varies, visual information begins to better perceive the left eye, and eggs, inkubirovanija in the dark, there are Chicks with equally sharp eyes.