People Born During Winter: Tend to Be More Lefty

According to a new finding, winter babies especially men born between November and January tend to be more lefty compared to others. The data showed that up to 9 per cent of all children born in winter are left handed.

This interesting observation was published in the journal Cortex and it found “in a survey of nearly 13000 adults from Austria and Germany, a great majority of left handed people, especially among men, were born during November, December, and January, with only 82 percent being born between February and October, and 10.5 percent being born between November and January.”
The lead author, Ulrich Tran, believes “this phenomenon is best explained by the theory that light exposure can lead to varied testosterone exposure in the womb.”

"Presumably, the relative darkness during the period November to January is not directly connected to this birth seasonality of handedness. We assume that the relative brightness during the period May to July, half a year before, is its distal cause", he explained.

Tran also added that “US neurologists Norman Geschwind and Albert Galaburda first argued that testosterone levels may influence handedness in the 1980s.”

Norman and his co-authors suggested that “Testosterone delays the maturation of the left brain hemisphere during embryonic development. The left brain hemisphere is dominant among right-handers, the right brain hemisphere is dominant among left-handers.”

Trans and his colleagues add to this theory, arguing that if a child's mother is exposed to more daylight while pregnant, her testosterone levels may rise high enough to affect the baby's own levels, potentially leading to a change in handedness.”

To find out the exact correlation in this case, future investigations are required.