Handedness
Facts
Left-handed women & the cancer link
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Facts
- Thumb sucking
Scientists at the Queen's University in Belfast, Northern Ireland, who studied ultrasound scans of 1,000 fetuses and traced the progress of some of these babies after birth, found that if a fetus preferred to suck its right thumb more than its left at around 10 to 12 weeks within the womb, the child will likely be right-handed after birth. Their report was published in the New Scientist magazine.
Moreover, they also discovered that the preference to move one hand over the other in the womb was associated with the handedness after birth.
The nervous system links to the body from the brain will only begin to develop around 20 weeks of gestation, it does not appear that the brain controls the choice of handedness at this early fetal age. Instead, it could be a local reflex arc involving the spinal cord.
Reference : The New Scientist Print Edition (22 Jul 2004)
- Hair
Check a baby's hair. If it swirls clockwise then 95%, the child would become right-handed.
Researchers from the National Cancer Institute in Frederick, Maryland have determined that a single gene might control both hair swirl direction and handedness and therefore, that could explain why our brains are asymmetrical.
Those who have one or two copies of the "right" version of the gene would be right-handed and have hair that swirls clockwise.
Those who have two "random" versions of the gene could be either right- or left-handed and have hair that swirls in either direction.
However, other scientists are unsure if a single, many genes or "random" genes determine right or left handedness because two left-handed parents can have a right-handed offspring or identical twins do not have the same handedness, one could be right-handed while the other is left-handed.
Reference : "Human handedness and scalp hair-whorl direction develop from a common genetic mechanism." Klar AJ. Genetics. (Sept 2003) 165(1):269-276
- Those who are ambidextrous are both left- and right-handed.
Left-handed women & the cancer link
- According to researchers at the University Medical Center in Utrecht in the Netherlands, left-handed women are more than twice as likely to suffer from breast cancer before reaching menopause as those who are right-handed.
The Dutch researchers examined over 12,000 middle aged women born between 1932 and 1941, over an 18-year period. They believe that an exposure to high levels of sex hormones in the womb can lead to left-handedness and changes in the breast tissue.
However left-handed women are advised not to be worried about these findings, because it is just not enough to link left-handed women with a complex condition like breast cancer. Larger-scale studies are needed to determine if there is indeed such a link.
Reference : "Innate left handedness and risk of breast cancer: case-cohort study" Made K Ramadhani, et al. British Medical Journal (26 Sept 2005)
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