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

The Chemical Lake

 Spotted Lake or Lake khiluk in Canada is richly concentrated with various minerals. It contains dense deposits of magnesium sulfate, calcium, and sodium sulfates. It also contains high concentrations of eight other minerals and lower amounts of silver and titanium. Most of the water in the lake evaporates over the summer, revealing colorful mineral deposits. Large ‘spots’ on the lake appear and are colored according to the mineral composition and seasonal amount of precipitation. Magnesium sulfate, which crystallizes in the summer, is a major contributor to spot color.  Originally known to the First Nations of the Okanagan Valley (Native American Tribe) as Khiluk, Spotted Lake was for centuries and remains revered as a sacred site thought to provide therapeutic waters. It is the most mineralized lake in the world. Each spot holds a different cure due to the unique chemical content found within each puddle. Lake Khiluk is considered a saline endorheic alkali lake. The Okanag...
Post a Comment
Read more

Why some flowers bloom at night ?

Summer is known for its fields of wildflowers and flowering trees. All colours of pedals spread toward the sky. We have taken for granted that flowers bloom during the day, just like how summer is warm and grass grows. However, there are some flowers that defy the norm and do not go with the flow of following daylight hours. These flowers actually have a good reason for their particularly weird flower habits. The main purpose of flower blossoms is for the plant to spread their seeds. The flower attracts bees, the bees fly to another flower, and voila, the flower has spread its seeds. However, bees are not the only pollinators, even if they are the most famous.  “7 Insect Pollinators that Arendt Bees or Butterflies”, moths, mosquitos, beetles, and even ants share the credit for helping flowers flourish. Most pollinators roam only in daylight, leading most flowers to open up when the sun is out to fit their pollinators’ schedule. But not all pollinators like t...
Post a Comment
Read more