Coincidence or cascade? The temporal relation between locomotor behaviors and the emergence of stranger anxiety.

Two infant milestones, self-propelled locomotion and stranger anxiety, tend to emerge at a similar age in development. An adaptive relation may exist in which the onset of one influences the development of the other in individual children. We examine whether these milestones systematically co-occur and whether one reliably precedes the other. In the current study, 104 parents completed weekly online surveys between 6 and 12 months, noting milestones as they occurred. Onset ages for locomotor behaviors were correlated with onset of stranger anxiety over and above a milestone in a third domain, namely consonant-vowel babbling. These data suggest that infants' earliest locomotor behaviors may play a role in galvanizing the development of stranger anxiety.
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