Skip to main content

What causes some people to be left-handed, and why are fewer people left-handed than right-handed?

Researchers who study human hand preference agree that the side of the preferred hand (right versus left) is produced by biological and, most likely, genetic causes. The two most widely published genetic theories of human hand preference argue that evolutionary natural selection produced a majority of individuals with speech and language control in the left hemisphere of the brain. Because the left hemisphere also controls the movements of the right hand--and notably the movements needed to produce written language--millennia of evolutionary development resulted in a population of humans that is biased genetically toward individuals with left hemisphere speech/language and right-hand preference.
 Approximately 85 % of people are right-handed. These theories also try to explain the persistent and continuing presence of a left-handed minority (about 15% of humans).
The genetic proposal to explain hand preference states that there are two alleles, or two manifestations of a gene at the same genetic location, that are associated with handedness. One of these alleles is a D gene and the other allele is a C gene.

 The D gene is more frequent in the population and is more likely to occur as part of the genetic heritage of an individual. It is the D gene that promotes right-hand preference in the majority of humans. The C gene is less likely to occur within the gene pool, but when it is present, the hand preference of the individual with the C gene is determined randomly. Individuals with the C gene will have a 50% chance of being right-handed and a 50% chance of being left-handed.

These theories of hand preference causation are intriguing because they can account for the fact that the side of hand preference of individuals with the C gene (most left-handers and some Right-handers) can be influenced by external cultural and societal pressures, a phenomenon that researchers have documented. These theories can also explain the presence of right-handed children in families with left-handed parents and the presence of left-handed children in families with right-handed parents. If the familial genetic pool contains C genes, then hand preference becomes amenable to chance influences, including the pressures of familial training and other environmental interventions that favour the use of one hand over the other.

 The proposed genetic locus that determines hand preference contains an allele from each parent, and the various possible genetic combinations are DD individuals who are strongly right-handed, DC individuals who are also mostly right-handed, and CC individuals who are either right-handed or left-handed. These genetic combinations leave us with an overwhelming majority of human right-handers and a small, but persistently occurring, minority of left-handers.



Credits: Nivethithaa
Labels:

Comments

Post a Comment

Popular posts from this blog

WHY ATLANTIC AND PACIFIC OCEAN ARE NOT MIXED?

Nearly 72% of the earth is filled with water and it is present with different names- oceans, seas, rivers. Why are they named differently? There are five oceans namely Artic ocean, Atlantic Ocean, Pacific Ocean, Indian ocean and Antarctic ocean . All the oceans are different in their physical and biological character called ocean clines. When we look at the Atlantic and Pacific Ocean junction, they do not mix. Is there any invisible Wall in between them? Many scientists have conducted research to solve this mystery. The Atlantic and Pacific Ocean have different chemical composition. The salinity of the water in the Atlantic Ocean is five times more than the Pacific Ocean. The density of water is also different, so even marine animals in Atlantic Ocean will not go to the Pacific Ocean. They cannot survive in other oceans. Atlantic and Pacific Ocean meet at Cape Horn. The narrow straight line formed by the water bodies is called Drake Strait. The Pacific Ocean is ...
Post a Comment
Read more

How did fruits get their names?

There is a variety of fruits in today's world. Each fruit has a name and the names are derived from foreign languages - modern and ancient. Some of these fruits have names that don't go with the fruit also. The name gooseberry has nothing to do with geese. It was originally called gorseberry. 'Gorse' in Saxton (a language spoken by early germanic people) means 'rough'. This fruit grows on a rough or thorny shrub. Just like the gooseberry, the fruit strawberry has no connection with straws. Strawberry is the changed name of 'strayberry'. The strawberry runners stray in all directions and hence the name. Peaches have been around for thousands of years. This fruit made its way to Europe when the Romans were around. The Romans called it 'persicum' meaning 'Persian apples. It was traded by the Persians during that time.  The national fruit of New Zealand kiwi was found in China. In other countries, it was called Chinese goo...
4 comments
Read more

5 Amazing Animal Temple

1) Crocodile Temple:      The Ananthapadmanabhaswamy Temple or Anantha Lake Temple is built for Lord Vishnu. It is also called a crocodile temple. This temple built in the middle of a lake in the little village of Ananthapura, around 6 km from the town of Kumbla in Manjeshwaram Taluk of Kasaragod District of Kerala. There is a harmless crocodile that lived in the Ananthapadmanabhaswamy Temple’s lake. It is a vegetarian. Believable of this place is that you will get lossed posting or objects after visiting this place. 2) Rat Temple:      The Karni Mata Temple is situated at Deshnoke in Rajasthan. This temple is the craziest place because it gives importance to rats. They believe that the god of this temple incarcerated every year as a rat. More than 25,000 black rats are living in this temple. White rats are considered a very holy animal in this temple. The food that gives to people as prasatham is the remaining food eaten by a rat....
3 comments
Read more