The question of whether every human is born right-handed or whether handedness develops later in life has fascinated researchers and scientists for decades. Handedness refers to the preference for using one hand over the other for tasks that require fine motor skills like writing, drawing, or throwing a ball. About 90% of the population is right-handed, while only 10% are left-handed. The remaining percentage are ambidextrous, meaning they use both hands equally. But is this preference innate from birth, or does handedness develop over time through genetics, environment, and experience?
Theories on Innate Handedness
There are several theories that support the idea that handedness is innate and present from birth:
Genetic Factors
Twin studies have shown that identical twins are more likely to share handedness than fraternal twins or non-twin siblings. This suggests there may be genetic components that contribute to being right or left-handed. Certain genes like LRRTM1 have been associated with increased odds of being left-handed. The exact genetics behind handedness are still being investigated, but it points to an innate biological basis.
Prenatal Hormone Exposure
Some research indicates that prenatal hormone levels, particularly testosterone, may influence the development of handedness in the womb. Higher levels of testosterone have been linked to a greater chance of being left-handed. This proposes that the foundations of handedness may already be present before birth.
Brain Lateralization
The left and right hemispheres of the brain have different functions – the left controls speech and language while the right handles spatial relations. Studies show the region that controls hand skill is localized on the opposite side of the dominant hand (e.g. left hemisphere for right handers). This suggests inherent differences in how the brain is wired could drive hand preference from birth.
Theories Supporting Learned Handedness
On the other hand, some theories posit that handedness is learned and shaped by external factors after birth:
Culture and Environment
Social and cultural pressures may push right-handedness as the norm. Things are designed for right-handed people – scissors, school desks, etc. Punishing left-handedness at an early age may lead children to adapt to using their right hand more often until it becomes their dominant hand.
Training and Experience
As motor skills develop through infancy and childhood, repetition and practice with one hand may gradually strengthen neural pathways for that hand. Early experiences and training may reinforce hand preference. For example, always feeding infants with the right hand may lead them to show a bias for right-handed gestures.
Gene-Environment Interactions
Rather than being purely genetic or purely learned, there are likely complex interactions between genes and the environment that shape handedness. While genetics may predispose someone’s hand preference, external factors help select which hand gets frequently used. The development of handedness likely involves both nature and nurture.
Evidence for Innate Handedness
So what does the research evidence actually show? There are several key findings that support innate origins of handedness:
Hand Preference in the Womb
Fetuses and infants demonstrate hand preference before cultural pressures come into play. One study found 75% of fetuses at 10 weeks gestation preferred sucking their right thumb over their left thumb. Another study of premature babies showed head position preference to one side correlated to their future dominant hand.
Hand Preference in Infancy
Well before being taught how to use a pencil or hold scissors, infants already show a bias in hand use:
- Reaching – 70-85% of infants preferentially use their right hand to reach for objects by 6-7 months.
- Gesturing – Infants favor gesturing with their right hand as early as 26 weeks.
- Role Differentiation – Around 6 months, infants show specialized use of their preferred hand for fine manipulation while the non-preferred hand supports.
This evidence of early hand preference supports innate origins rather than learned handedness.
Consistency Across Cultures
If social and cultural pressures primarily determined handedness, then rates of left-handedness should vary dramatically between cultures. However, while subtle differences in handedness rates exist around the world, the majority of humans across cultures are right-handed:
| Country | Left-handedness Rate |
|---|---|
| France | 10-13% |
| India | 6-10% |
| Japan | 8-15% |
| Netherlands | 4-7% |
| Spain | 6-10% |
This universal tendency argues for a biological basis rather than learned handedness.
Critical Periods in Developing Handedness
While there is strong evidence that handedness originates before birth, researchers have proposed “critical periods” where the development of hand preference can be shaped and reinforced:
Prenatal Period
As mentioned earlier, factors like genetics, hormone exposure, and brain lateralization may establish the foundations for handedness before birth. This sets up the initial bias.
6-24 Months of Age
As infants begin actively reaching, grabbing, and manipulating objects, they strengthen neural pathways for their preferred hand. Hand preference becomes more pronounced and consistent around 6-24 months old.
2-4 Years Old
Between 2-4 years old may be another critical period where handedness can still be influenced. Consistently encouraging use of the non-preferred hand may help develop ambidexterity. But it becomes difficult to shift the established preferred hand.
Older Childhood
By around 5-6 years old, hand preference is strongly established and difficult to change. From this point on, the preferred hand gets specialized for precise fine motor tasks.
So while not set in stone, there appears to be a developmental trajectory that makes handedness increasingly stable yet still malleable within certain age ranges.
Can Handedness Change?
Because handedness develops over time, especially in infancy, some individuals do switch their hand preferences:
Infants
Up to 24 months, hand preference in infants is still flexible. In one study, 6% of infants shifted between a right and left preference over a 6 month span. Forces that may cause switches include neglecting the preferred hand due to injury.
Early Childhood
Preschool aged children can successfully change their handedness if guided consistently. In one experiment, 6 out of 13 left-handed preschoolers shifted their writing hand after training. But the new preference was less strong.
Older Children & Adults
Attempting to switch handedness gets more difficult with age as preference is ingrained. Only 1 of 22 adults and older children succeeded in shifting from their dominant hand in a study. It requires months of concerted training.
So while malleable in infancy, handedness gets progressively fixed – making switches harder – by around 5-6 years old. But it’s still possible with considerable effort.
Is True Ambidexterity Possible?
What about people who seem equally skilled with both hands – are they truly ambidextrous? Research shows mixed findings:
Motor Skill Symmetry
Strictly equal motor proficiency in both hands is extremely rare, even in those who identify as ambidextrous. There is usually a slight asymmetry with one hand still faster or more precise.
No Hand Preference
Ambidextrous people do lack a clear hand preference for common tasks and switch between hands fluidly. But subtle biases still emerge under conditions of speed, precision, or environmental pressure.
Separate Hand Roles
Rather than no preference, ambidexterity may involve specialization of each hand for different roles – e.g. dominant hand for writing, non-dominant for sports. But the non-dominant hand usually trails slightly in skill.
Genetic Predisposition
There seem to be genetic links to ambidexterity as well. Having one left-handed and one right-handed parent makes children more likely to use both hands well due to receiving varied predispositions.
True equal skill across all tasks with both hands seems uncommon. But ambidexterity does allow flexible handedness compared to right or left dominance.
Why Do Some People Not Have a Dominant Hand?
For the majority of people, one hand clearly emerges as the preferred dominant hand. But why do some remain ambidextrous without a strong asymmetry between their hands?
Genetic Predisposition
As mentioned earlier, carrying genes for both right and left-handedness from parents may predispose a child to ambidexterity and make them less lateralized.
Neuromotor Delay
Some studies have associated delayed development of handedness with delayed development of other neuromotor skills like sitting and walking. Ambidexterity may persist if maturation is slightly slower.
Environmental Reinforcement
Actively encouraging and rewarding use of both hands from early childhood onward can help strengthen neural pathways for ambidexterity before single hand dominance sets in.
Brain Differences
One brain imaging study showed less lateralized activation in the frontal and motor regions of ambidextrous individuals. More balanced brain development could allow equal hand skill.
So while multiple factors may disrupt the establishment of a dominant hand, inherent neurobiological differences in the brain may be the key reason some people remain truly ambidextrous.
Conclusion
In summary, the bulk of the evidence indicates that handedness – either right, left, or ambidextrous – has origins that begin before birth and are shaped by genetics, hormone exposure, and brain lateralization. Hand preference emerges in infancy, becomes reinforced during critical periods of development, and is strongly established by around 5-6 years old. While influenced by external forces, handedness appears to be largely innate rather than learned from training and culture. An underlying neurobiological basis makes switching handedness difficult after early childhood. So while not an absolute rule, the majority of humans worldwide seem to possess an innate tendency for right-handedness from very early on in life.