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For left-handed people, the world may seem like an inappropriate place. From scissors to sports equipment, most things aren’t just made for them.
The reasons for left-handedness is a scientific mystery, but neuroscientists believed that there are some reasons that give a solution to this question of why are some people left-handed.
If you know that older left-handed people are more likely to have learned to eat or write with their right hand, and in many parts of the world it is still common for children to be forced to use their right hand. In some places word "sinister" is used for left-handed people that is generally wrong.
Some studies including twins have claimed that up to 25 percent of handedness can be described by a person's genes expressions, while 75% is determined by environmental factors.
What is Handedness?
According to human biology, Handedness is a personal hand preference for better, faster, or more precise performance for hand use, known as a dominant hand.
A hand that is incapable, or less chosen is called a non-dominant hand.
Left-handedness is a rare form and it is estimated that about 10% of the world's population is left-handed, The remaining 90% of the general population is right-handed.
Handedness often defined as someone writing by which hand, as it is quite common for people to choose to do certain tasks with each hand.
However, mixed-handedness is rare, with most people choosing one hand for most works.
There are about 708 million left-handers in the world.
In 200 studies published on left-handedness with an overall sample size of more than 2.3 million individuals, they discover that the left-hand percentage is about 9.2 percent.
As about 7.7 billion people live in the world in 2019, it can be guessed that there are about 708,400,000 left-handers.
Preference for being left-handed is likely decided in the womb.
Studies since the 1980s have claimed that our hand preference for being left or right-handed is likely decided in the womb before we are born, at the beginning of the eighth week of pregnancy, according to the ultrasound scan.
From 13 weeks in the womb, babies begin to suck their right or left thumb.
The spinal cord is key for hand selection.
It was earlier thought that genetic differences in the left and right hemispheres of the brain would decide that a person was born left or right. But a 2017 research, printed in the journal Elife, discover that the solution may be in the spinal cord.
They discover that gene activity in the spinal cord is asymmetrical in the uterus, and this may be what causes the left or right-handedness.
Hands and arm movements begin in the brain, in a part called the motor cortex, which forwards signals to the spinal cord. When the baby is developing in the womb, for about 15 weeks, the motor cortex and spine are not yet linked, but the right or left-handedness is already fixed.
The child can move and pick up his favorite hand before the brain begins to control the body. These researchers believed that the spine is the decider for hand selection.
Men are more likely to be left-handed than women.
An analysis of 144 left-handedness studies with a total sample size of 1,787,629 members showed a 2 percent more left-handedness in men compared to women.
Can Animals also be left-handers?
Yes, Humans are not the only type representing the left-handedness, in the current meta-survey of paw selections in cats and dogs, they show that cats are about 36% to 46% left-pawed. While in dogs, there are about 31-53% lefties.
This shows that left-handed growth is not something that is typical for humans but can be seen in other species as well. However, the lower percentage of lefties about 10% in humans seems definite to us, as these scales are generally higher in animals.
Other animals, such as chimpanzees or polar bears, also have left-handers, chimpanzees prefer the right or left side of the body to the other when using equipment or in search of food.
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