Why are some people right-handed and some are left-handed?

Answer 1

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 percent of people are right-handed. These theories also try to explain the persistent and continuing presence of a left-handed minority (about 15 percent 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 (for dextral, meaning “right”) and the other allele is a C gene (for “chance”). 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 percent chance of being right-handed and a 50 percent 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 favor 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.

Answer 2

What has been said by biologist is a crap. That opinionated.

The fact : - (we are groomed into using our right hand)

Long before.. ....it didn't matter if people were left or right handed..

As people got civilised, many cultures developed good practise..
like one hand for *** and the other for food

This kind of disease preventing cultures took lead


Later on, tools that were designed were meant mainly for the right hand

Then came writing ..
The English alphabets have a right hand stroke .. that's why you see lefty's curving their hand so that the stroke would be smoother

Soon parents knew that if they didn't train their children to use the right hand ... they would probably having a hard time in society...

Hence KF C was correct when young.

If you travel a lot .. you will notice that 3rd world country will have more left handed people than first world countries ... simply because 1st world countries are more informed about these things ... and have their children correct at a young age

I hope this answers your question clearly

('',)
Peace!

Answer 3

Scientists have been trying to answer this question by looking at the current lateralization research and comparative research on lateralization (mainly regarding language). Others do this by studying the development of handedness.

Genetic theories do not posit that there are genes for handedness, but the presence of certain alleles may leads to lateralization. Hand preference is a "side-effect" of this lateralization.

Source(s):
www.pubmed.com
keywords, lateralization, handedness and hand use preference
Marian Annett has written extensively on the genetic theory.

jollyroger- there may be more of a proportion of lefties in other countries, but there is still a right shift. Yes, there is a developmental set of events that lead to right handedness, but we are not "groomed". Self generated experience can lead to hand use preference as well, not just people making kids be right handed on purpose.

Answer 4

Yet, another reason that proves that the world we live in is crazy!!

My answer would be that more people feel comfortable doing things like writing with their right arm, while some feel more comfortable with their left hands. It's not wrong to be left-handed, or right-hanhded.

Answer 5

It's their genes...maybe their earlier generations used to be left-handed or right-handed. Some theory said that left-handed people is much cleverer than those who are right-handed. Well, that may not be true...

Answer 6

Researchers have discovered proof that as far back as 500,000 years ago, 10% of people were left-handed. So there should still be some benefit to being left-handed, even in the world we live now.

If between moms and dad one is left-handed that rises the chance to 19% and when both parents are left-handed the possibility rises into 26%. These stats suggest that handedness is at least somewhat hereditary. Left handedness is highly uncommon, since it's not just caused by recessive and dominant genes. About 90% of individuals are right-handed, recommending that right-handedness is an incredibly dominant quality. Based on exactly what we know about genetics, a gene that is so fiercely dominant, right-handedness would push away left-handedness a long time ago.

Their theory is that there are two unique alleles of a gene which causes handedness. We have learned in school that an allele is a variation of a gene, one of those alleles is understood as the D gene, which stands for "dextral", meaning. The other allele is called the C gene, which means possibility. The D gene is the most common in the human gene pool when it is present, the person will be always be right-handed. You may for that reason also believe that the existence of the substantially less typical C gene will suggest the person is left-handed.

https://youtu.be/ic_16vhi-rE

Answer 7

Well first of all, it depends on which side of the brain a person uses more (left side of brain controls right side of body and vice versa). Secondly, anyone can learn to use both hands, it only requires practice and conditioning of the other side of the brain.

Answer 8

I remember when I was a kid, I actually wanted to get used to writing on both sides. But my aunt insisted I write with my right. So ever since then, I've been right handed.

Answer 9

maybe they were practicing it since they still a kid..
i have a friend who left-handed..she said that she's been using left hand to write since she still young..most people that i met who using left hand to write is totally a genius person..

Answer 10

Maybe its the hand they use most when there a baby.