Free Newsletters - Space News - Defense Alert - Environment Report - Energy Monitor
by Brooks Hays
Vienna (UPI) Jul 3, 2013
The vast majority of humans are right-handed. Only about ten percent are left-hand dominant. But what causes the ten percent to prefer their opposite set of digits? Scientists have long traded theories on the matter and argued whether genetics are at play.
Recently, in a survey of handedness involving 13,000 Germans and Austrians, researchers found that male southpaws are slightly more likely to be born in November, December and January than other months -- proof, they say, of a hormonal mechanism at work.
The study was led by psychologist Ulrich Tran, a researcher at the University of Vienna, in Austria; the study was published this week in the scientific journal Cortex.
"Presumably, the relative darkness during the period November to January is not directly connected to this birth seasonality of handedness," said Tran. "We assume that the relative brightness during the period May to July, half a year before, is its distal cause."
Tran and his colleagues say their new research confirms an earlier theory, proffered in the 1980s by American neurologists Norman Geschwind and Albert Galaburda. They hypothesized that testosterone levels were essential in tipping the scales that determine handedness. Most right-handed people are left-brain dominant, and left-handed are right-brain dominant. And testosterone has been shown to delay the development of the left brain hemisphere during embryonic stages.
Thus, Geschwind and Galaburda concluded, heightened testosterone levels may enable a preference for the right side of the brain and the left hand.
The theory remains controversial, but Tran and his colleagues say the prevalence of left-handedness in winter babies corroborates the now-decades-old logic. Winter babies are conceived in spring, and in their earliest embryonic stages during summer, increased daylight hours can lead to heightened levels of testosterone in women.
Excited as Tran and his study co-authors are, the researchers acknowledge more research is needed determine "the exact way of causation."
All About Human Beings and How We Got To Be Here
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.|