Testosterone and left-handedness

Austrian psychologists from the University of Vienna believe that left-handed people are due to hormonal failure. "Responsible" men for it is testosterone, which slows down the development of the left hemisphere of the brain in the embryo. "We were surprised to learn that most left-handed men are born in late autumn and winter - in November, December and January. Only in the three months were born 8, 2% of left-handers, while from February to October - 10, 5%, "- said the head of research Ulrich Tran.

He suggested that boys conceived in the spring, were more susceptible to the sun's rays, the ability to increase testosterone levels, which is why the right hemisphere of the brain of infants formed faster and gets dominance over the left. "In right-handers, on the contrary, is more developed left brain," - said the expert, adding that the "restructuring" of the body may occur, including, and because of illnesses and injuries. Testosterone levels in the expectant mother during pregnancy also plays a role. "The higher the score, the more likely a woman to give birth Lefty" - said the scientist who first made about the effect sezonnosti.

For reference:
Past studies on this subject have shown that only 2% of left-handers are born in a family of right-handers. This probability increases to 17% if one parent is left-handed. If the main hand and left my mom and dad, the child will be left-handed in 46% of cases.

Source: www.medikforum.ru/news/medicine_news/34503-uchenye-vyyasnili-chem-obuslovlena-levorukost.html