More left-handed men are born during the winter, study says

July 3, 2014
The front and back of a human right hand. Credit: Wikipedia.

Men born in November, December or January are more likely of being left-handed than during the rest of the year. While the genetic bases of handedness are still under debate, scientists at the Faculty of Psychology, University of Vienna, obtained indirect evidence of a hormonal mechanism promoting left-handedness among men. Psychologist Ulrich Tran and his colleagues published their findings in the scientific journal Cortex.

Various manual tasks in everyday life require the use of the right hand or are optimized for right-handers. Around 90 percent of the general population is right-handed, only about 10 percent is left-handed. The study of Ulrich Tran, Stefan Stieger, and Martin Voracek comprised two large and independent samples of nearly 13000 adults from Austria and Germany. As in modern genetic studies, where a discovery-and-replication-sample design is standard, the use of two samples allowed testing the replicability and robustness of findings within one-and-the-same study. Overall, 7.5 percent of women and 8.8 percent of men were left-handed. "We were surprised to see that this imbalance was caused by more left-handed men being born specifically during November, December, and January. On a monthly average, 8.2 percent of left-handed men were born during the period February to October. During November to January, this number rose to 10.5 percent", according to Ulrich Tran, lead author of the study.

A hormonal cause during embryonic development

"Presumably, the relative darkness during the period November to January is not directly connected to this birth seasonality of . We assume that the relative brightness during the period May to July, half a year before, is its distal cause", explains Ulrich Tran. A theory, brought forth in the 1980s by US neurologists Norman Geschwind and Albert Galaburda, posits that testosterone delays the maturation of the left during . The left brain hemisphere is dominant among right-handers, the right brain hemisphere is dominant among left-handers. Intrauterine are higher in the male fetus, because of its own testosterone secretion, than in the female fetus. 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.

Previous studies on the subject provided mixed and inconsistent evidence. There was no clear indication which season has an effect, and whether seasonality affects men, women or both sexes equally. According to the current findings, there is a small, but robust and replicable, effect of birth seasonality on handedness, affecting only . These results are consistent with a hormonal basis of handedness, corroborating thus an old and controversial theory. However, the exact way of causation needs to be investigated in future studies.

Explore further: Men, women in more satisfying relationships have lower testosterone

More information: Latent variable analysis indicates that seasonal anisotropy accounts for the higher prevalence of left-handedness in men. Ulrich S. Tran, Stefan Stieger, Martin Voracek. Cortex, 57, 188-197, 2014. DOI: dx.doi.org/10.1016/j.cortex.2014.04.011

Related Stories

Men, women in more satisfying relationships have lower testosterone

April 11, 2014
(Medical Xpress)—Many people assume that the more testosterone, the better, but a new University of Michigan study finds that might not always be the case in romantic relationships.

Left-handed fetuses could show effects of maternal stress on unborn babies

June 2, 2014
Fetuses are more likely to show left-handed movements in the womb when their mothers are stressed, according to new research.

Lefties aren't so gifted after all

December 11, 2013
Despite popular belief, left-handers are no more gifted than their right-handed counterparts, with Flinders University research finding that some left-handed children actually have significantly lower cognitive abilities.

Low testosterone levels may indicate worsening of disease for men with prostate cancer

May 5, 2014
For men with low-risk prostate cancer, low levels of testosterone may indicate a worsening of their disease. That's the conclusion of a new study published in BJU International. The findings may help physicians identify patients ...

What makes us left or right handed? New study rules out strong genetic factors

October 1, 2013
Around 10 per cent of the UK is left handed—and that percentage remains consistent in many populations around the world. But why exactly someone is left or right handed remains unclear.

Male health linked to testosterone exposure in womb, study finds

April 22, 2014
Men's susceptibility to serious health conditions may be influenced by low exposure to testosterone in the womb, new research suggests.

Recommended for you

Gene immunotherapy protects against multiple sclerosis in mice

September 21, 2017
A potent and long-lasting gene immunotherapy approach prevents and reverses symptoms of multiple sclerosis in mice, according to a study published September 21st in the journal Molecular Therapy. Multiple sclerosis is an ...

Neuron types in brain are defined by gene activity shaping their communication patterns

September 21, 2017
In a major step forward in research, scientists at Cold Spring Harbor Laboratory (CSHL) today publish in Cell a discovery about the molecular-genetic basis of neuronal cell types. Neurons are the basic building blocks that ...

Highly precise wiring in the cerebral cortex

September 21, 2017
Our brains house extremely complex neuronal circuits whose detailed structures are still largely unknown. This is especially true for the cerebral cortex of mammals, where, among other things, vision, thoughts or spatial ...

Your neurons register familiar faces, whether you notice them or not

September 21, 2017
When people see an image of a person they recognize—the famous tennis player Roger Federer or actress Halle Berry, for instance—particular cells light up in the brain. Now, researchers reporting in Current Biology on ...

Faulty cell signaling derails cerebral cortex development, could it lead to autism?

September 20, 2017
As the embryonic brain develops, an incredibly complex cascade of cellular events occur, starting with progenitors - the originating cells that generate neurons and spur proper cortex development. If this cascade malfunctions ...

Strategy might prevent infections in patients with spinal cord injuries

September 19, 2017
New research led by The Ohio State University Wexner Medical Center found a potential therapeutic strategy to prevent infections in patients with spinal cord injuries.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.