When do you know whether your baby is right- or left-handed?

[By: Lisanne Schröer]

When you grab your keys to go to work in the morning, or when you make a grocery list, which hand do you use? Simple tasks in our daily life like these involve an important aspect of motor planning: hand preference.

If you are a parent of a young baby, you might have seen them using both hands equally when, for example, they are trying to feed themselves. This, while almost all adults have a hand preference for which hand you use. Have you ever wondered when we start to have a preference for which hand we use in everyday tasks?

 

Handedness
In humans, about 90% of us are right-handed [1]. Hand preference refers to which hand we prefer to use for a task that we typically do with one hand [2]. However, preference for using for example your right hand versus your left hand is not the only aspect of hand preference. How strongly we prefer one hand above the other is also a defining factor [3]. Even if you recognise yourself as left-handed, there may be several things you prefer to do with your right hand (or the other way around). Surprisingly, research has shown that right-handed people on average have a stronger hand preference than left-handed people, meaning that left-handers use their non-preferred right hand for more tasks [4]. Even more so, a very few of us are ambidextrous or show a mixed hand preference [5].

Development
The earliest precursors of handedness can be detected in unborn babies. The majority of unborn babies move their right arm more than their left arm from around the 10th week of pregnancy, and most unborn babies mostly suck their right thumb from the 15th week of pregnancy [6].

However, hand preference typically emerges in the first two years of life. Some demonstrate a consistent preference for one hand over the other from very early stages of life, while other show a more variable preference. Generally, by the age of two, most children have established a consistent hand preference [7].

Hand preference for grasping objects emerges around 6 months of age, while hand preference for manipulating objects starts to show around 10 to 11 months of age. By 13 to 14 months of age, children start to have a clear preference for using one hand over the other in tasks where they need to use both hands simultaneously, each for a different purpose. An example would be a task that involves holding a piece of paper with one hand and using a pair of scissors to cut the paper with the other hand. This preference becomes stable around 18 months of age [7]. Hand preference in other task might take a longer time to stabilize. For instance, a study found that a consistent hand preference for grasping Lego blocks in the process of constructing a tower appears around 4 years of age [8].

Origin
Although the exact origin of handedness is unknown, researchers have suggested that hand preference is related to the hemispherical specialization of one hemisphere in fine motor skills [6]. The movements of hands are controlled by the opposite side of your brain. Simply put, your right hand is controlled by the left hemisphere, while your left hand is controlled by the right hemisphere [1].

Researchers often suggest that hand preference has a strong genetic component. Children whose parents are both left-handed are three to four times more likely to be left-handed than children whose parents are right-handed [9].

Animals
Interestingly, other animal species also show a hand preference, varying per individual. However, most species do not show population-level handedness, like the majority of humans are right-handed [10]. Although, there are some exceptions. Most kangaroos, for instance, appear to have a preference for the left paw [11].

Primates, such as chimpanzees, gorillas and macaques have shown to have a consistent individual hand preference [12]. The development of their hand preference seems to be quite similar to the development in human children. For instance, chimpanzees also show their hand preference by two years of age, which is found to be stable through adolescence [13]. The hereditability of hand preference is also found in primates like chimpanzees [14].

Conclusion
All in all, hand preference becomes stable over infancy and early childhood. Every child seems to have their own trajectory. Some infants may show a stable preference from very early on, while others take more time to demonstrate a clear preference. Most children show a consistent hand preference by the age of two, although for some tasks it may develop or become apparent earlier than for other tasks.

So how early might you tell if your baby is right- or left-handed? According to some sources, right-handed babies tend to turn their head to the right side when placed on their tummies, while left-handed babies regularly turn their head to the left or have no preference for both sides [15]. But only time will show whether this also applies to your child.

 

References
[1] Sharoun, S. M., & Bryden, P. J. (2014). Hand preference, performance abilities, and hand selection in children. Frontiers in Psychology, 5: 82. https://doi.org/10.3389/fpsyg.2014.00082
[2] Annett, M. (1970). A classification of hand preference by association analysis. British Journal of Psychology, 61(3), 303-321. https://doi.org/10.1111/j.2044-8295.1970.tb01248.x
[3] Steenhuis, R. E., & Bryden M. P. (1989). Different dimensions of hand preference that relate to skilled and unskilled activities. Cortex, 25(2), 289-304. https://doi.org/10.1016/S0010-9452(89)80044-9
[4] Yahagi, S., & Kasai, T. (1999) Motor evoked potentials induced by motor imagery reveal a functional asymmetry of cortical motor control in left- and right-handed human subjects. Neuroscience Letters, 276(3), 185-188. https://doi.org/10.1016/S0304-3940(99)00823-X
[5] de Kovel, C. G. F., Carrión-Castillo, A., & Francks, C. (2019). A large-scale population study of early life factors influencing life-handedness. Scientific Reports, 9: 584. https://doi.org/10.1038/s41598-018-37423-8
[6] Corballis, M. C. (2014). Left brain, right brain: Facts and fantasies. PLOS Biology, 12(1): e1001767. https://doi.10.1371/journal.pbio.1001767
[7] Michel, G. F., Campbell, J. M., Marcinowski, E. C., Nelson, E. L., & Babik, I. (2016). Infant hand preference and the development of cognitive abilities. Frontiers in Psychology, 7:410. https://doi.org/103389/fpsyg.2016.00410
[8] Sacrey, L.-A. R., Arnold, B., Whishaw, I. Q., & Gonzalez, C. L. R. (2012). Precocious hand use preference in reach-to-eat behaviour versus manual construction in 1- to 5-year-old children. Developmental Psychobiology, 55(8), 902-911. https://doi.org/10.1002/dev.21083
[9] Bryden, M. P., Roy, E. A., McManus, I. C., & Bulman-Fleming, M. B. (1997). On the genetics and measurement of human handedness. Laterality: Asymmetries of Body, Brain and Cognition, 2(3/4), 371-336. https://doi.org/10.1080/71375429
[10] Warren, J. M. (1980). Handedness and laterality in humans and other animals. Physiological Psychology, 8(3), 351-359. https://doi.org/10.3758/BF03337470
[11] Giljov, A., Karenina, K., Ingram, J., & Malashichev, Y. (2015). Parallel emergence of true handedness in evolution of marsupials and palacentals. Current Biology, 25, 1878-1884. https://doi.org/j.cub.2015.05.043
[12] Annett, M., & Annett, J. (1991). Handedness for eating in gorillas. Cortex, 27(2), 269-275. https://doi.org/10.1016/S0010-9452(13)80131-1;
Regaiolli, B., Spiezio, C., Hopkins, W. D. (2018). Hand preference on unimanual and bimanual tasks in Barbary macaques (Macaca Sylvanus). American Journal of Primatology, 80(3): e22745. https://doi.org/10.1002/ajp.22745;
Meguerditchian, A., Phillips, K. A., Chapelain, A., Mahovetz, L. M., Milne, S., Stoinski, T., … Hopkins, W. D. (2015). Handedness for unimanual grasping in 564 great apes: The effect on grip morphology and a comparison with hand use for a bimanual coordinated task. Frontiers in Psychology, 6: 1974. https://doi.org/10.3389/fpsyg.2015.01794

[13] Hopkins, W. D. (1995). Hand preferences for simple reaching in juvenile chimpanzees (Pan troglodytes): Continuity in development. Developmental Psychology, 31(4), 619-625. https://doi.org/10.1037/0012-1649.31.4.619
[14] Hopkins, W. D., Dahl J. F., & Pilcher, D. (2001). Genetic influence on the expression of hand preference in chimpanzees (Pan Troglodytes): Evidence in support of the right-shift theory and developmental instability. Psychological Science, 12(4), 299-303. https://doi.org/10.1111/1467-9280.00355
[15] Coren, S. (1992). The left-hander syndrome: The causes and consequences of left-handedness. Detroit, MI: Free Press. As cited in: Lehnardt, K. (2016, September 23). 62 interesting left handed facts [Blog post]. Retrieved from: https://www.factretriever.com/left-handedness-facts

Photo references
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Photo 3 by Porco Rosso on Unsplash