One small step for man…

 Exactly when babies take their first step is a big moment. It symbolises a new phase. Walking means that a baby’s head is higher up and they can see more. They can reach more things, which  means more mess and more tidying up for their carers! (Figure 1)

Walking on two feet, known as bipedalism, is a trait that separates humans from other primates. It is one of the earliest human traits to evolve (Pontzer, 2012) and it brings with it advantages. Fossils suggest that ancestors of modern day humans have been bipedal for several million years.  So it is fundamental to what makes us human.

 Today in the field of psychology, walking is considered as an aspect of gross motor development, which relates to the ability to maintain the position of the whole body and move about. This is different to fine motor development, which refers to becoming more skilled at using the hands to reach, lift and manipulate objects, including drawing, folding and block building (Bowler et al., 2023). Both fine and gross motor development are vital parts of infant and toddler development and are associated with later conditions such as learning disability and developmental coordination disorder (Bowler et al., 2024). Motor skills impact many aspects of a child’s life, including learning, relationships, play, and growing independence.

Is Timing Everything?

 So what influences when a child takes their first step?  Babies vary a lot in when this important milestone happens. Most children will begin walking sometime between 8 and 18 months (WHO, 2006). However, as shown in Figure 2 below, there are wide differences among children in when they first take a step on their own. Not much is known about what causes these wide differences in age at onset of walking.

Learning to walk independently takes a lot of practice. Past research has shown that onset of walking is influenced by many factors such as practice, cultural differences in childrearing routines and physical development (Adolph et al., 2018; Karasik & Robinson, 2022).  But one aspect of walking that was not understood is the role of genetics.  Our group is interested in finding out more about the way in which genes influence infant development alongside environment (Ronald & Gui, 2024).

Nature AND Nurture

In our study, we were interested to discover if genetics influences when a child starts walking and if genetics is involved, we wanted to understand what these genes do (Gui et al., 2025).  We analysed samples of over 70,000 infants for whom we knew which month they had started to walk. We discovered that about a quarter of the differences between babies in when they learn to walk is due to common genetic differences that we had measured (Figure 3). 

The genes operate in newborn brains

We found that the genes we discovered as influencing age at onset of walking were expressed in the brain. They appear to play a part in influencing the structure of the brain in both newborn babies’ brains and in adults’ brains. The genetic influences affect the amount of folding on the outer surface of the brain and they affect the size of the motor regions in the brain (Figure 4).

Links with ADHD and education

Interestingly, we see that the genetic influences on age at onset of walking also overlap with the genetic influences on ADHD and on educational success. Somewhat later onset of walking within the typical range was linked genetically with less chance of developing ADHD. In these children raised in Europe, relatively later onset of walking was influenced by some of the same genes involved in higher educational attainment.  

It took 80 years to complete

Science is sometimes quite slow, but 80 years?! Our study began officially four years ago, in March 2021, when our funding began from the Simons Foundation.  But the 70,000 infant participants come from several different cohorts. The oldest cohort in our study were born in 1946. So our project did indeed take nearly 80 years from start to finish! (Figure 5). We are very grateful to all the cohorts who collaborated with us, and all the participants of course!

A message for parents

Watching and waiting for your child to reach development milestones can be nerve-wracking and it is normal to worry a bit about your child’s development. Our study shows that there are very wide differences between children in when they take their first step. Our study suggests that from a genetic point of view, being a bit later than average to take a first step unaided is not a concerning sign. When your child takes their first step on their own is partly due to their genetics.  Enjoy your child’s achievements and allow them to experiment with movement at their own pace. Always visit your doctor if you have concerns with their development.

What’s next for the science

We are keen to continue this work in other ancestral groups. We were only able to identify European ancestry cohorts with walking measures when we started this project. It is also important to understand how genes and environment work together to influence infant development.  We have many ideas, but as they say, one step at a time!

 References

Adolph, K. E., Hoch, J. E., & Cole, W. G. (2018). Development (of Walking): 15 Suggestions. Trends in Cognitive Sciences, 22(8), 699–711. https://doi.org/10.1016/j.tics.2018.05.010

Bowler, A., Arichi, T., Austerberry, C., Fearon, P., & Ronald, A. (2024). A systematic review and meta-analysis of the associations between motor milestone timing and motor development in neurodevelopmental conditions. Neuroscience and Biobehavioral Reviews, 167, 105825. https://doi.org/10.1016/j.neubiorev.2024.105825

Bowler, A., Arichi, T., Fearon, P., Meaburn, E., Begum-Ali, J., Pascoe, G., Johnson, M. H., Jones, E. J. H., & Ronald, A. (2023). Phenotypic and Genetic Associations Between Preschool Fine Motor Skills and Later Neurodevelopment, Psychopathology, and Educational Achievement. Biological Psychiatry. https://doi.org/10.1016/j.biopsych.2023.11.017

WHO multicentre growth reference study group, de Onis, M. (2006). WHO Motor Development Study: Windows of achievement for six gross motor development milestones. Acta Paediatrica, 95(S450), 86–95. https://doi.org/10.1111/j.1651-2227.2006.tb02379.x

Gui, A., Hollowell, A., Wigdor, E. M., Morgan, M. J., Hannigan, L. J., Corfield, E. C., Odintsova, V., Hottenga, J.-J., Wong, A., Pool, R., Cullen, H., Wilson, S., Warrier, V., Eilertsen, E. M., Andreassen, O. A., Middeldorp, C. M., Pourcain, B. S., Bartels, M., Boomsma, D. I., … Ronald, A. (2025). Genome-wide association meta-analysis of age at onset of walking. Nature Human Behavior.  https://doi.org/10.1038/s41562-025-02145-1

Karasik, L. B., & Robinson, S. R. (2022). Milestones or Millstones: How Standard Assessments Mask Cultural Variation and Misinform Policies Aimed at Early Childhood Development. Policy Insights from the Behavioral and Brain Sciences, 9(1), 57–64. https://doi.org/10.1177/23727322211068546

Pontzer, H. (2012). Overview of Hominin Evolution. Nature Education Knowledge , 3(10), 8–8.

Ronald, A., & Gui, A. (2024). The potential and translational application of infant genetic research. Nature Genetics, 56(7), 1346–1354. https://doi.org/10.1038/s41588-024-01822-7