Males born in winter are more likely to be left-handed and a hormonal mechanism may have something to do with it, a new study suggests.
The genetic bases of what determines whether a person is left or right-handed remains a mystery, andi In an attempt to find an answer, researchers from the University of Vienna stumbled upon an interesting find. Their study revealed that males born in winter months are more likely to be left-handed than males born in other months of the year.
The study, published in the online journal Cortex, was conducted on 13,000 adults from Austria and Germany. Among these, 7.5 percent of women and 8.8 percent of men were left-handed. On further analyses of the male participants, researchers found that 8.2 percent of left-handed men were born during the period February to October. This number increased to 10.5 percent during the months of November to January.
Researchers said that a hormonal mechanism may be responsible. How? Intrauterine testosterone levels are higher in the male fetus than in the female fetus because males have their own testosterone. However, the testosterone level of the mother and external factors may also affect intrauterine testosterone levels. Specifically, more daylight may increase testosterone levels, making a seasonality effect plausible. Testosterone delays the maturation of the left brain hemisphere during embryonic development, a region that is mainly active in right-handed people.
Given all that, it's somewhat ironic that International Left-Handers Day is celebrated in the summer, on August 13, and that a good number of male VIP left-handers were born between June and September – Bill Clinton, Barack Obama, George Bush, just to name a few. Here's a list of some of the most famous people in the world that are left-handed. You'll find most of them were born in the summers, not winters.
