Which babies are more likely to be left-handed?
Psychologists at the University of Vienna looked at 13.000 adults and found that overall, 7.5 per cent of women and 8.8 per cent of men were left-handed. Further research showed that among the men, 8.2 per cent of the left-handers were born during winter periods and particularly from February to October. Yet during November to January, this number rose to 10.5 per cent.
The researchers said that according to their findings, which were published in the scientific journal Cortex, this fact could have a hormonal cause. More specifically, an embryo’s exposure to higher levels of the male hormone testosterone in the womb is believed to increase the chances of being left-handed.
More daylight may increase testosterone levels, and as baby boys born in the winter are in the embryonic stage during the spring and summer, they may be exposed to more testosterone. The effect is explained for men, but not women, because male brains are exposed to substantially higher testosterone levels than female brains during prenatal development, as we read in Daily Mail.
The Geschwind-Galaburda hypothesis, named after the neurologists who devised the theory, suggests that testosterone delays the maturation of the left brain hemisphere during embryonic development. We have to mention that the left brain hemisphere is dominant among right-handers, while the right brain hemisphere is dominant among left-handers.