The development of handedness in toddlers

Everything Baby does can feel like a clue about who they're going to grow into, but questions as basic as which hand they'll use to sign their name aren’t always easy to figure out in children as young as Baby is. For something that can seem so simple, handedness is a complex scientific question, and it’s still not clear exactly why anyone turns out to be a righty or a lefty, so the fact that you and Baby aren’t sure which one they are going to be isn’t too much of a surprise. As they grow, though, which hand they favor will become more and more clear.

Handedness development timeline

Between the ages of 2 and 3, it’s common to start to see toddlers favor one hand over the other for certain tasks, and by the age of 5 or 6, handedness is usually pretty set in stone. It’s not necessarily a one-or-the-other question, though – many people, both children and adults, have one hand that they favor for certain tasks, like eating, and the other hand for other tasks, like building with blocks, throwing a ball, or counting on their fingers.

A 2013 Canadian study suggests that handedness preference might develop earliest when it comes to food, and then later spread to other tasks. On the other hand, when adults talk about handedness, writing hand is one of the main things they discuss, but most toddlers don’t start penning their first masterpiece until at least the age of 4 or 5. In the end, there are some children who start to show a strong hand-preference earlier on, while others stay somewhat ambidextrous for a while longer, and a few stay ambidextrous their whole lives.

Theories about handedness

The two poles of speculation about how handedness forms are, first, that handedness is mostly genetic, or, second, that it’s largely environmental. Evidence suggests that the truth falls somewhere in-between. If handedness was totally genetic, there wouldn’t be sets of identical twins who have different hand-preferences. On the other hand, if handedness wasn’t at least somewhat genetic, there probably wouldn’t be such a strong tendency towards right-handedness – only about one-tenth of people are left-handed. Left-handedness also runs fairly strongly in families, though not entirely, which leads some researchers to speculate that there’s a gene or series of genes for right-handedness, and that children who don’t have the genetic tendency towards right-handedness are just as likely to grow up to be right-handed as left-handed.

Most researchers and experts believe that the question of handedness is more complicated than just a question of genetics, or just a question of environment. It’s not clear what does cause handedness, but there are several factors that have been shown not to determine handedness, including a child’s health at birth, their parents’ employment situation or familial income, parental attitudes, or the learning resources available to them as they grow.

  • Donna M. D’Alessandro. “When Will I Know Which Hand She Will Use?”, February 28 2011. Web.
  • Jason W. Flindall, Claudia L.R. Gonzalez. “On the Evolution of Handedness: Evidence for Feeding Biases.” PLoS One. 8(11). Web. 2013.
  • David W. Johnston, Michael E.R. Nicholls, Manisha Shah, Michael A. Shields. “Nature’s Experiment? Handedness and Early Child Development.” Demography. 46(2): 281-301. Web. May 2009.
  • Jyoti Madhusoodanan. “Babies Don’t Develop Handedness All At Once.” Inside Science. American Institute of Physics, December 26 2013. Web.
  • David M. Rosenbaum. “On Left-Handedness, Its Causes and Costs.” The New York Times. The New York Times, May 16 2000. Web.

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