Statistics shows that the ratio of right-/left-handers is 90% vs. 10% in the population.
In a very old paper by Marianne Annette (sp?) (I think it was developed in the late 1970's) she proposed, based on inheritance analysis, that there is a genotype for right handedness, but none for left handedness. Instead, left handers emerge from a more ambidextrous genotype that is highly influenced by environment (possibly internal). This would explain the relatively small number of left handers and the odd pattern of inheritance. Since the PCSK6 gene expression is correlated with degree of handedness rather than side of handedness, then it is possible that this is related to Annette's original theory.
I am a left-hander from Germany. While some of my left-hander friends were forced to use the right hand when they were children (as otherwise they might be classed as abnormal) I had very liberal parents that left it to me (the only thing they ask me is to use the cutlery to Western standard). I still do a lot of things with my left hand but as many devices are designed for right-handed people only I would call myself mixed handed.
I think it is a random choice by nature but biased by society.
The answer to this question is at the root of the mechanism of evolution of dynamical systems. Left-handed and right-handed are the one of degree of freedom of the dynamical system which can be compared with a bisexual life. At this stage of evolution it is a cause and effect of brain splitting. Humanity is a product of finding the next golden section between synthesis and analysis by Life on Earth. The process of brain splitting on next stage will be continues by lefties in future.
Handedness is intimately tied to the fact that each side of the brain is connected to the opposite side of the body. During development, axons growing from cell bodies on the left side of the brain somehow need to find their way across the midline to their destination on the right, and vice versa for axons starting from cells on the right. In order for this to occur, there must be two different neurotrophic gradients in existence during the developmental period when the axons are growing, oriented in opposite directions, or if there is only one gradient to guide the contralateral growth, axons from the different sides must be differentiated so that right side axons grow in the direction of the increasing gradient, while axons from the other side grow in the direction of the decreasing gradient.
Thus the relationship between the brain and extremities such as hands and feet is intrinsically asymmetrical, and the phenomenon to be explained is why so many neurobehavioral properties are so symmetrical, not only in other species, but even in humans. It's easy to think of evolutionary and developmental constraints that provide adaptive advantages for symmetrical behavior, such as the advantages of being able to walk in a straight line.
We can speculate that only when hominids began to walk upright that the constraint on symmetrical development of forelimbs was released, and the deeper neurodevelopmental asymmetry became evident as handedness. One evolutionary prediction from this line of thinking is that the more distant a bipedal genetic lineage is from a quadrupedal common ancestor, the more likely it is to exhibit strong handedness.
Related to the dominant hemisphere.
Not learned.
Can be genetically determined, but any insult to the left hemisphere during birth may also shift the pattern.
Re. the disproportion between handedness, maybe having most people right-handed promotes some degree of conformity for more societal stability; but having a small percentage left-handed introduces a limited degree of innovative possibilities from people who may approach things differently from the majority.
All above discussions were excellent.
We proposed a Neural Circuit Calibration (NCC) theory in neuroinformatics [Wang and Fariello (Harvard), 2012, JAMA 1(2)], which can be applied to explain handedness. The NCC theory is based on a fundamental principle that the neural signals transmitting in human nervous system are unique in the form of Pulse Frequency Modulations (PFM) [Wang, 2013].
The NCC theory indicates that, although all neural circuits have been built-in and ready when a baby is born, the brain of the baby cannot yet distinguish the locations and empirical meanings of all mixed neural signals, because they are identical inside the central nervous system as PFM signals.
Therefore, there is a necessary initialization process known as NCC for any new-born baby. NCC is a cognition process that identifies and matches the sources/targets of neural signals as well as their spatial and cognitive meanings interpreted in the brain. The calibration process will take about one to two years to be mature. That is why a new-born baby has to try (or play) almost everything accessible by any hand, and even to taste his/her own toes or shoes.
It’s apparent that before NCC, both hands are equivalent in principle because the symmetry of human nervous system, particularly the peripheral subsystem. Therefore, the theoretical distribution of left-handers and right-handers would be even. However, parents’ and social selections during the NCC period do greatly biased the results of the normal distribution. After the NCC process, the dominate hand of a baby is established and then be strengthen during 2 to 3 years old. (Typical parents’ and social selections during the NCC period will be discussed later.)
As has been implied, the brain is plastic and responsive to social factors. It also appears that dominance is graduated, with a range from highly dominant (highly reliant on one side) to minimally dominant (ambidextrous). These would combine so that genetic and social components would interact to result in a ratio biased towards the socially accepted norm ie right handed. So the core of handedness is genetic but overlayed with a plasticity mediated by social factors.
I don't think handedness is learned (though some social conditioning could influence expression of this trait), but more at the innate end of the spectrum. Left-handeness seems to be at least partly inherited. There is also some evidence that other primates can show strong handedness, and that it can be very asymmetric in distribution (e.g. most gorillas being right-handed). The small percentage of human left-handers are showing a behavioural consequence of somewhat differently arranged neural circuits. This could be beneficial to society as a whole, perhaps as a gain in spatial abilities, for example. Left-handed is 'right-brained'!
In the initial neural circuit calibration phase of new born babies, does the brain determine the form of handedness? Or, do the handedness stimuli influence the development and structure of the brain? The causation needs to be clarified. According to the Neural Circuit Calibration (NCC) theory, the later is the cause, and the former is the effect.
The recent report on gene PCSK6’s dominate role in handedness forming would be doubtful. If handedness is really determined by PCSK6 or other genes, why there are much more left-hander babies born from right-hander parents?
Philosophically, or more generally, may human genes carry any non-genetic information such as social habits, acquired knowledge, passions, motivations, and etc.? Obvious it’s not because all higher-layer human behaviors are acquired where is no direct genes influence.
I was not allowed to write left in the primary school, but experimented with both hands, as I was older. As a result, I write (and actually do all other activities) with both hands equally well and change hand unconsciously, having an additional degree of freedom that way. So I think, even though there is some genetical tendency, learning has a huge influence.
In a very old paper by Marianne Annette (sp?) (I think it was developed in the late 1970's) she proposed, based on inheritance analysis, that there is a genotype for right handedness, but none for left handedness. Instead, left handers emerge from a more ambidextrous genotype that is highly influenced by environment (possibly internal). This would explain the relatively small number of left handers and the odd pattern of inheritance. Since the PCSK6 gene expression is correlated with degree of handedness rather than side of handedness, then it is possible that this is related to Annette's original theory.
A study from Psychological Science (vol 12, no 4), summarized here: http://www.apa.org/monitor/oct01/chimps.aspx says that handednes is biologically determined in chimps.
Does it apply to us as well?
I agree with the NCC theory. I believe babies are influenced by their immediate environment in the choice of which hand they use in doing stuff. Just like other things learnt, practice makes perfect!!!
Doesn't the preponderance of right-handers suggest a large influence of predetermination of handedness? Surely if it's a completely learned and therefore to some extent chosen activity, the split between left and right handers would be more even? This is coming down from a time when there was no 'social pressure' to be right handed as presumably early humans had no particular cultural associations with choice of a particular hand, only functional ones - which worked better for each individual.
People are different. Type of handedness -also. Some left-handed people will use their left hand inspite of strong enviromental influence, some will change the dominance if it is not strongly pronounced. Some children seems to "play with their handedness" changing through the ontogenesis the dominant hand.
Cultural intolerance of left-handedness can drive down its prevalence. In relatively tolerant societies that was indeed taken historically to be 1 in 10, though some recent studies show something closer to 1 in 8. How good is a study at including people with pathologies thought to raise the prevalence of left-handedness? If 1 in 8 are left-handers, could there be two genes, one of them recessive?
If I may add to what Hanna, Gordon, Elizaveta and Stephen have suggested, perhaps we can view chirality as we currently do synesthesia? The latter - like the former - have had to endure tolerance effects because as Ramachandran notes, a surprisingly inordinal number of breakaway artists have had the synesthetic capacity. A similar number of athletes (especially in baseball switchhitters) enjoy an equal advantage which perturbs pitchers. My older brother is also greatly ambidextrous, as is (was) my older sister. He was allowed to select handedness, and can use both, but excels with the left athletically. She was not allowed and "became" right handed. Their stereo vision had a similar preferential option the rest of us do not have (monocular control, which was "remediated" in childhood).
Nature loves to try things out, by affording a few of us options no one else has. The many get fearful and influence the few not to be synesthetic or acknowledge chiral options most of us do not have. To me, neither "lefties" nor synesthetes are either a disorder nor a predetermined trait; they are simply a novel option -- and extra choice -- some have and most do not. This discomfits those of us without that choice. What surfaces are our cultural fears, perhaps, not gene expression. Darwin wrote that he could not find where experimental variety even ended - we just give up where we start calling it "individuality" - when every single member is only a member of its own unique self and nothing else. If we could not see color, and a few were born who could, we would treat color the same way - and miss the beauty of diversity in experimental preference Nature might have afforded.
A genius is one of the million. Thank god i wasn't in a devastating time for any devastating chosen-side-hand.
Annett's hypotheses were that handedness was genetically determined, later on she thought that hemispheric dominance is genetically determined, and handedness is a by-product consequence of h. dominance.
An insightful review of such positions are available in a Corballis' paper on cerebral specialisation (1989, Psychological Review Vol. 96, No. 3,492-505: laterality and Human evolution), and in a further work by the same author (1997, Psychological Review
Vol. 104, No. 4, 714-727: The genetics and evolution of handedness), that puts more emphasis on genetic issues. In the former one, M. Corballis pays attention to cultural pressures to have right-handed people, and how that may influence ratio of rh and lh (cfr Sthephen Williams).
You can find a clear explanation of Annett's theory by the author herself with graph of rh and lh distribution in this paper: Laterality and types of dyslexia (Neuroscience and Biobehavioural reviews Vol 20 Nr 4, p 631-636), attached.
According to these authors, genetics would determine right dominance (R+), not left (cfr Peter gordon' and Stehephen williams' aswers).
Neuroanthropology has offered a potential hypothetical solution; see macneilage, et al, sci am, june, 2009.
Left hemisphere is specialized for routine, predictable behavior; with most behavior automatic or routine, driven be internal codes/representations, this results in a strong left hemisphere, activating right body side; right hemisphere, in contrast, is a novelty detector, processing non-routine or low-frequency occurring information; this is characteristic of every vertebrate brain; for example, whales are right-jawed; songbirds are left hemisphere dominant for song; birds in general are left hemisphere dominant for pecking at food towards the right side, a routine feeding behavior; chimps demonstrate right hand preference greater than left; most of us are right handed; left hemisphere specialized for frequently occurring behavior; so, the arguement runs along these lines.
For example, consider an eagle chasing it's prey of a rabbit; a running rabbit will slowly move to the right, reflecting left hemisphere dominance and "strength" for engaging in a routinized behavior; this becomes predictable to the eagle, making it easier for the eagle to predict the rabbit will eventually move right; so eagle anticipation of rabbit moving towards right makes rabbit "easy" prey; this is too dangerous for the preservation of the rabbit species, endangering survival; so mother nature's gene pool includes a small percentage of rabbits who have less hemispheric specialization, making some move more to the left, as in left handedness, or some showing no preference at all; effective for adaptation, making prey movement less predictable, helping to ensure survival of the rabbit species because the movement becomes less predictable, rendering the eagle's anticipation of a "right direction" movement ineffective - sort of equivalent to a baseball pitcher throwing a hitter a curve ball instead of a predictable moving fast ball.
So, making a very long story extremely short..., there is likely a genetic influence on degree of specialization of hemispheric functions; this has been demonstrate experimentally and summarizrd by macneilage and others. So..., in the human vertebrate brain, this right-left handed difference can perhaps represent an evolutionary vestage or "leftover" of a behavior or pattern/degree of hemispheric specilization that was once very adaptive for survival in a predatory environment. This view does not contradict what others have stated, but..., it makes behavior biologically consistent across various species of the vertebrate brain. Please also see m. Kinsbourne on the development of handedness, hemerisphic specialization, and the development of attention, anticipation, and metacognition - various papers. I hope you understand the simple example; if curious, contact me backchannel, at [email protected].
Sounds unbelievable, but makes good adaptive evolutionary, phylogenetic sense; lk
Leonard - that is awesome, thank you so much for sharing. Just what I have been looking for too. Noack (2012) and Schirmer and Kotz (2006) inspire such wonderful thoughts but the trail backward is not always easy to follow - now this elegant explanation you shared. Yes, I think so too; the left, the outer, the upper, the newer suggests a pattern of gradual inhibitory regulation of what are naturally explorative drives. Possibly to accommodate dense social adaptation (regularization itself)? Would appreciate your thoughts on this.
Probably because the genes also are influenced by the enjoyment factors (from an very early age in the uterus)
There are unquestionable genetic influences according to neuroanthropological data; please refer to the paper in the scientific american i cited in my prior reply. There is a definite advantage to hemispheric specilization; the fact that we live in a right-handed world did not happen by chance; left hemisphere specializes for routine, frequently occurring behavior; this activates right side body plane; this has been demonstrated in experimental studies on numerous occasions; this is not to say a person is unable to learn to use the right hand if they are left handers; i am right handed; i learned to use my left for a computer mouse because of my desk set-up; people who are left handed typically are left handed for a certain percentage of activities; they learn to use the r hand because the environment is constructed for right handers; it also has been demonstrated that weaker hemispheric lateralization of functions is adaptive for certain circumstances; bilateral representation of cognitive functions is adaptive in injury recovery; for example, people with bilateral representation of cognitive function show bilateral cognitive deficit after localized stroke; however, they also recover more quickly than a solid right hander. So of course, interactions exist; but, the question as i read it related to the majority of the population; left and right handedness is not equally distributed because of the inherent advantages of hemispheric specialization. Nature does nothing randomly; mother nature is the only individual who can ever have things "both ways," having her cake and eating it, too; but..., there is good reason for this.
Just read the article attached above (MacNeilage, Rogers & Vallortigara 2009) - a very enjoyable read, and confirms my instincts about the genetic influence and long history of handedness, or rather 'brainedness', in our own and other species. Thanks Leonard for bringing it to our attention!
There is a very well done (and pleasant) podcast by RADIOLAB on this matter: http://www.radiolab.org/story/whats-left-when-youre-right/
They provide some informative figures and historic perspectives concerning evolutive hypotheses, and some surprising ratio of distributions among species.
I read an article in a popular magazine a little over fifty years ago. (I remember where I was when I read it, therefore an approximation of when.) It said that eye dominance indicated whether you were naturally left handed or right handed. If you look through a telescope or a sight with your left eye, you are naturally left handed.
I was in the Army at the time and the next time I went to the range, I tried left handed. The first clip was much lower than with my right eye, but by the time I used the third clip, I was scoring higher. Overall, I qualified higher than before. The next time I fired, I scored even higher.
After that, took the article as the truth.
Very interesting; i recall reitan stating many years ago about the lack of relationship between eyedness and handedness. I also read this some years ago but i am unable to recall when and where.
An alternate explanation of your experience, perhaps...?
The learning, and subsequent "switching" of the brehavior of shooting a rifle, is novel. In "theory," a novel task, defined as a "low frequency" occurring event, would preferentially activate right hemisphere in a right handed person; the novelty of the task should activate right menisphere; since direct connections are quicker in neural transmission than indirect connections, theory predicts learning/re-learning the "shooting" task would be easier with the left eye; if aiming with right eye when learning/re-learning the task, information first activates left hemisphere and then should be transfered to the right hemisphere because of the level of novelty and right hemisphere preference for managing "spatial" information; this transfer from left hemisphere to right hemisphere takes a bit more time - a longer route to travel, resulting in less efficient performance, especially in right-handed people.
This would also predict that left handed baseball batters/hitters would be the best hitters against right handed pitchers, since when the ball is released by the pitcher, it immediately activates the right hemisphere in view of the spatial characteristics of the task of hitting a baseball - the ball is immediately exactly where you want it, in the left visual field re: right hemisphere activation. I tried to prove this once, but the major leagues do not keep information on natural handedness of baseball players; the league keeps no information on hand preference. A left handed person, more likely to have bilateral hemispheric representations, should therefore have the easiest time of it. An interesting question to play with.
After learning to play the piano as a child I found that learning to touch type as an adult at 40 years was quite easy. Both are ambidextrous skills but I have always been right handed for writing.
Handedness for handwriting is one issue, performing tasks that by nature require bimanual coordination is another. In fact, even writing is a "bimanual" type of task insofar as the right might be used for fine motor control while the left is used as background, to hold the paper steady. Piano playing and keyboarding, playing a saxophone or the drums, are just to name a few tasks that by very nature require some sort of bimanual coordination; so, perhaps somewhere along in this discussion, somebody should provide an operational definition of what they might mean by handedness/hand preference; also, the question seems reductionistic by making this an either or issue in terms of genetics versus learned habitual behavior; anomalous motor development, with lack of complete suppression of certain transitional reflexes in late infancy/toddler years, can also be associated with hand preference differences as described within literature on motor development. And, these anomalies need not be associated with specific learning disabilities. Procedural learning is not restricted by handedness, nor is handedness restricted by procedural learning skills that require bimanual coordination. As we dive more deeply into task demands, operationalizing what we mean by handedness seems to become increasingly important; it is common to be right handed for writing while demonstrating a certain level of ambidexterity in keyboarding, etc. The fact is that we were born with two hands to move two hands, not just one. Task demands play a role, and certain tasks might be better performed with one hand or the other based upon environmental characteristics and requirements.
Because of the continuous periodic interest in my answer to this question, it makes sense to note that at the moment I would answer a bit differently and more expandedly, because the understanding of the integrity of dynamic systems has changed significantly over five years. This is a matter of fundamental understanding of evolution.
Synchronization and unification of the glossary is necessary to begin. Then there a subject to understanding will rise, one can go to the understanding of the Superstructure, unified bidirectional processes of self-organization in dynamical systems, the general principles of periodicity (not popularized discreteness), memory (as the structure dissipation invariants) and coherent evolution. Further, it is possible to consider in detail the ordered branching from syngenesis as the brain evolves, as well as related issues on the scale of ordered branching from eukaryotic cell and rest questions of the chaos theory.
None of the classical divisions of science is able to completely understand the integrity and evolution within framework of the classical demarcation agreement that creates isolated islands of cognitive biases. For example, physics suffers from this, since even understanding of so-called full unification is beyond the limits of demarcation, same as the constantly ignored observer. For same reason, physics and physicists are poorly aware of self-reference and forced to almost recklessly rely on formalism without wondering of what physically ensures the functioning of formal logic in the thought processes of a biological organism or a computer and where semantics comes from.
It looks some out of topic (but for someone has long been obvious). This is personal message for those who pay attention to my previous comment here.
NB: By the way, biological systems hint that a direct process and a wave of relaxation are spatially (topologically) separated (humans with various behaviour, plants vs animals etc.) - it is not only the separation of time scales (by speeds) of forward and relaxation processes. From the other hand, it cannot be said that this is simple imprint of the previous dynamics in the form of a superstructure memory - synthesis and analysis occur continuously as topological structure evolves and, as usual, is for any structure scale the bunch [spectral width by duration of the cycle] must be?
It's a very interesting question, because it shows a cultural prejudice. There's nothing of genetic about right/left-handedness, but as well as a lot of abilities they are acquired by chances or by education. Anyway a lot, too many, people continue thinking about genetic origins. I think the problem consists of an ambiguous understanding and unclear knowledge of what our genes are capable to induce.
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