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Maturation plays a very strong role in motor development. Preterm infants reach motor milestones later than do full-term infants (Gabriel et al., 2009). Cross-cultural research also supports the role of maturation because around the world, infants display roughly the same sequence of motor milestones. Among some Native Americans and other ethnic groups around the world, it is common to follow the tradition of tightly swaddling infants to cradleboards and strapping the board to the mother’s back during nearly all waking hours for the first 6 to 12 months of the child’s life. Although this might lead one to expect that swaddled babies will not learn to walk as early as babies whose movements are unrestricted, studies of Hopi Native American infants have shown that swaddling has little impact on when Hopi infants initiate walking (Dennis & Dennis, 1991; Harriman & Lukosius, 1982). Such research suggests that walking is very much maturationally programmed. Other evidence for the maturational basis of motor development comes from twin studies. Identical twins, who share the same genes, have more similarities in the timing and pace of motor development than do fraternal twins, who share half of their genes (Fogel, 2007; Wilson & Harpring, 1972). Samples of young children in the United States show no ethnic or socioeconomic status differences in gross motor skills such as running, hopping, kicking, and catching (Kit, Akinbami, Isfahani, & Ulrich, 2017).

Advancements in motor skill are influenced by body maturation and especially brain development. The pruning of unused synapses contributes to increases in motor speed and reaction time so that 11-year-old children tend to respond twice as quickly as 5-year-olds (Kail, 2003). Growth of the cerebellum (responsible for balance, coordination, and some aspects of emotion and reasoning) and myelination of its connections to the cortex contribute to advances in gross and fine motor skills and speed (Tiemeier et al., 2010). Brain development improves children’s ability to inhibit actions, which enables children to carry out more sophisticated motor activities that require the use of one hand while controlling the other, such as throwing a ball, or that require both hands to do different things, such as playing a musical instrument (Diamond, 2013). As infants and children gain experience coordinating their motor skills, activity in the areas of the brain responsible for motor skills becomes less diffuse and more focused, consistent with the lifespan principle that domains of development interact (Nishiyori, Bisconti, Meehan, & Ulrich, 2016).