Timing and Developmental Dynamics in the Acquisition of Early Motor Skills

In nearly all developmental studies, age is the independent variable. Assigning an age metric to the x-axis is so common that we rarely examine the assumptions behind it. What does the passage of time mean to a living organism? How is it that we expect time itself to explain change of form and function? Or, on a deeper level, what enables an organism to “keep time,” that is, to exhibit time-dependent regularities — stages so consistent that most developmentalists can quite accurately determine the age of a human infant or a rat pup by body morphology, or by seeing only snatches of posture, movement, or social behavior.