What are the Odds of Being Left Handed?

Approximately 10% of the world’s population is left-handed; about 90 percent of people are right-handed, with 1 percent being ambidextrous. Hence left-handers are outnumbered about 9 to 1 by right-handers. [1]

Moreover, the odds of a man being left-handed are 1.23 times higher than the odds of a woman being left-handed. [2]

What Causes a Child to be born Left-handed?

Left handed doodling

Whether right or left, a person’s preferred hand has long fascinated researchers. But the reason some 10 percent of people turn out to be left-handed remains a mystery. Although left-handedness is still often associated with awkwardness, it is no longer as widely discouraged or discriminated against as it once was.

Although researchers have failed to identify solid factors that influence hand preference, they have found that handedness is linked to how the brain is wired. [4]

It has been suggested that there may be a genetic link, but no definite proof has been found. Theories include:

Genes

The tendency to favor one hand over the other may have a strong genetic component. If a child inherits a single gene that predisposes him to be left-handed, he will probably show this characteristic, depending on environmental factors.

Fetal Development

It is believed by some researchers that the likelihood of being right-handed or left-handed is more influenced by environmental factors than by genetics. Researchers theorize that prenatal exposure to hormones may influence an individual’s later preference for using one hand over the other.

Adjustment

People who are naturally right-handed may switch to being left-handed after suffering an injury to the right side of their body.

Gender

Some researchers have hypothesized that the male hormone testosterone may influence right- and left-handedness.

Do Lefties Think Differently?

Left-handed

Some scientists believe that left-handers think differently than right-handers, and they have some evidence to back up their claims.

Hand Preference Development

It was previously thought that a single gene controlled handedness, but more recent studies suggest that multiple genes (up to 40) contribute to establishing hand preference. [5]

Research published in Neuropsychologia shows that fetuses as early as the fifteenth week of pregnancy show a strong preference for arm movement. By week fifteen, 90% of fetuses will prefer right-sided thumb sucking. These early preferences are correlated with handedness later in life. [6]

The Brain Difference

A 2019 study found that the brains of left-handed people differ from their right-handed peers in three main areas: the motor cortex for both sexes and the striatum and cerebellum in male participants. These areas are involved in motor function. [7]

The Dominance of Right Handers 

Left-handed people are forced to deal with a world built for right-handers. They have to find creative ways around furniture and other products that were not made for their dominant hands, which makes them think differently about how things are used in day-to-day life.

Odds of Having a Left-Handed Child?

Little girl drawing with pencil at home

The chance of having a left-handed child if both parents are right-handed is approximately 1 in 10. The likelihood of a child being left-handed is 2 in 10 if the father is left-handed, 3 in 10 if the mother is left-handed, and 4 in 10 if both parents are left-handed. [8]

The following table presents the percentages of having a left-handed child for each possible parent combination:

Father Mother Percentage chance of Left-Handed Child
Left Left 20%
Left Right 12%
Right Right 9%
Right Left 16%

Source: [9]

Countries that have The Most Left Handed People?

Countries Percentage of left-Handed People
The Netherlands 13.2%
United States 13.1%
Belgium  13.1%
Canada  12.8%
United Kingdom 12.24%
Ireland  11.65%
Switzerland  11.61%
France  11.15%
Denmark  11%
Italy  10.51%

According to research, the highest incidence of left-handedness is in Western countries. The Netherlands, the United States, Belgium, and Canada lead, with around 13% of the population being left-handed, while the UK trails close behind. [10]

Countries that have the Least Left Handed People?

Countries Percentage of left-Handed People
Korea  2.0%
Mexico  2.5%
China  3.5%
Japan  4.7%
Taiwan 5.0%

From the data above, it can be clearly seen that the percentage of left-handed people is much lower in countries with more traditional cultures. Also, this is the top reason why people have more complex writing styles in many Asian countries. 

A study compared the development of laterality (preferences for using one hand over another) in two cultures that differ in pressure against left-handedness.

Tunisian children, whose parents prohibit left-handedness, were compared to French children, whose parents encourage the use of either hand. Researchers tested 5-, 7-, and 9-year-olds for hand preference, right-left performance differences, eye preference, and foot preference.

When Tunisian right-handers were compared with French right-handers, they held the stylus in their right hands as consistently as did their French counterparts. They also performed better than the French on a pegboard task involving both hands.

The results of this study suggest that cultural pressure may influence handedness early in life, leading to right-handedness in children who might otherwise have been ambidextrous or left-handed. [11]

Number of Left-Handers Males vs. Left-Handers Females

In a 2008 study, researchers found that left-handed individuals are 23% more likely to be male than female. [12]

This means that there should be roughly 5 times as many left-handed men as there are left-handed women.

Little-Known Facts about Left-Handers 

  • Studies have found that people with psychosis are 20% more likely to be left-handed. [13]
  • According to a study from Georgetown University Medical Center, left-handed people may listen more effectively to slow-changing sounds than right-handed people do. [14]
  • Left-handed people make up 10 to 12% of the world population. However, this number is slowly increasing as left-handedness becomes more socially acceptable.
  • The research book ‘Cerebral Dominance: The Biological Foundations’ found that a study of left-handed people revealed they were 11 times more likely to suffer from allergies than right-handed people. [15]
  • In a 2011 study, researchers found that 94% of left-handed patients exhibited periodic limb movements during sleep compared with 69% of right-handed patients. [16]
  • In 2008, the Illinois Research Consortium found that left-handed people can handle two simultaneous tasks better than right-handed people. When given two tasks to complete at once, lefties completed both much faster than their right-handed counterparts. [17]

References

  1. https://www.mcgill.ca/oss/article/health-general-science/are-you-left-handed-science-still-yearns-know-why
  2. http://www.eric.ed.gov/ERICWebPortal/search/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=EJ807817&ERICExtSearch_SearchType_0=no&accno=EJ807817
  3. https://www.livescience.com/19968-study-reveals-lefties-rare.html 
  4. https://www.betterhealth.vic.gov.au/health/healthyliving/left-handedness#bhc-content 
  5. https://ghr.nlm.nih.gov/primer/traits/handedness 
  6. https://www.sciencedirect.com/science/article/abs/pii/002839329190080R 
  7. https://link.springer.com/article/10.1007/s00429-019-01941-6#citeas 
  8. https://link.springer.com/article/10.1007/BF01067772
  9. http://www.anythingleft-handed.co.uk/lefty-probability.html
  10. https://www.betterhealth.vic.gov.au/health/healthyliving/left-handedness#bhc-content 
  11. https://www.sciencefocus.com/science/are-there-more-left-handed-people-where-writing-flows-right-to-left/ 
  12. http://eric.ed.gov/?id=EJ807817
  13. https://www.everydayhealth.com/healthy-living-pictures/little-known-facts-about-lefthanders.aspx
  14. https://gumc.georgetown.edu/news-release/what-your-hands-are-doing/
  15. http://www.hup.harvard.edu/catalog.php?isbn=9780674106598
  16. https://journal.chestnet.org/article/S0012-3692(16)54569-3/abstract
  17. https://s18798.pcdn.co/craiglab/wp-content/uploads/sites/4477/2016/09/Craigetal_2012_PSPB_sexismcontrol-rwiibg.pdf