First of all, raise your hand and say
It is generally believed in the medical field that the hand held by the newborn baby will become the dominant hand after the birth of the fetus.
Second, genetic theory.
Another study tends to be influenced by genetic factors. In a family where both parents are left-handed, the probability that the child is left-handed is 50%. In a family where both parents are right-handed, the probability that the child is left-handed is only 2%.
Third, gene theory.
Some people also use dominant genes and recessive genes to explain the causes of handedness. Right-handed genes are dominant and left-handed genes are recessive. Only in special gene pairing can the traits of left-handed recessive genes be expressed, so left-handed people become a minority in the total population. It is also reported that a person's habit of using his left hand or his right hand is determined by a single gene, and the medical profession is trying to find out this gene.
Fourth, age theory.
There are also studies that left-handed people are determined by their mothers' age at birth. According to ABC statistics, the probability of giving birth to left-handed women over 40 years old is higher than that of pregnant women under 30 years old 128%.
Five, testosterone theory
It is also a decisive factor for mothers. Another theory is that pregnant women exposed to higher doses of testosterone may be the reason why children are left-handed. This theory holds that exposure to testosterone during pregnancy will lead to different brain development in different doses. Testosterone inhibits the growth of the left half of the brain, so more nerves migrate to the right half of the brain. The highly developed right brain has a great influence on language and handedness.
So the fetus naturally becomes left-handed after birth, because the right brain mainly controls the movement of the left side of the body. This theory holds that exposure to higher doses of testosterone is also related to learning disabilities, dyslexia and stuttering.
Extended data:
About 6%- 13% people in the world are left-handed. According to this calculation, there are at least 80 million left-handed people in China, and the number is still rising.
For a long time, some people think that left-handed people can develop their right brain and be smarter. According to experts, there is not much difference in general cognitive ability between left-handed and right-handed people, regardless of historical research or neurology, and each has its own potential.
The human brain is divided into left and right brains, and the division of labor is completely different. The left brain dominates the activities of the right hemisphere and is responsible for processing language, abstract thinking, logical reasoning, numerical operation and so on. , so it is called "rational hemisphere"; The right brain dominates the activities of the left hemisphere, and is responsible for processing image thinking such as spatial imagination, music and rhythm, which is called "artistic hemisphere". People who are used to using their left hand generally help to stimulate the development of the right brain; Using the right hand helps to stimulate the development of the left brain.
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