Developmental Milestones: Fact or Myth?
As parents, we are almost constantly comparing our child to someone else's child (or even to our own children who have already gone through that phase of life), and there always seems to be something to fret about. Are you worried that your child isn't saying enough words yet, or isn't walking and he's already a year old? These are common concerns, especially for new parents.
In my undergraduate and graduate training (and as a parent) I have learned that all of these milestones, as they are called, should really be taken "with a grain of salt." Your child is unique, and although I am glad that researchers took the time to examine 'what is normal development' this results in average time frames, where very few children actually fit exactly the time frames that the development textbooks mention. Ok, so now you can calm down. (Note: If your child is far past what the milestones say then this may be cause for concern, and you should talk with your pediatrician.)
Recently, researchers have come to realize that we cannot only describe the 'normal' progression of infant and child development by time frames and say that this is a universal truth. Instead, Thelen (1995) for example wrote a piece entitled "Motor Development: A New Synthesis" which appeared in American Psychologist (a prominent scholarly journal). This author explains that motor development (which is typically what we parents talk about, i.e., "Yay! Johnny is walking now!" and "Oh! I had to baby-proof the house, because Amber is crawling!", etc.) is caused by a variety of factors (i.e., "multicausal").
Exploration and Selection in Infant Development
I will not go into all of the technicalities, but basically there is no "innate" quality in your child of crawling, walking, reaching, etc. All of these 'milestones' as we call them come about through exploration and selection. The first step for your child is for him to "discover" movements that get him "into the ball park" that the task demands--"a tentative crawl or a shaky few steps" (p. 86). Then, gradually your child will tune this new movement through repetition of action and perception of the consequences. For example, early in infancy your baby may flail his arms instead of grabbing the toy next to him, but this random flailing gradually becomes more and more fine tuned as he realizes what it takes to make his arms function in grabbing the toy. (In the figure below, imagine the square as being an infant and the circle as a toy. Then, the black lines are the infant's attempts at grabbing the toy. Over time, the infant tunes this motor skill. For instance, notice the concentration of lines toward the toy over time. Pardon my paint drawing skills.).
Instead of an innate quality in the brain that determines that your baby will reach correctly at a certain age it is just that we as human beings have bodies that are all similar enough that we all come to the similar conclusions on the best way to reach (or walk--for instance, the author mentions that if we were on the moon we would likely all come to the conclusion that jumping was the best way to get around, and thus it would appear that jumping is innate around a certain age, even though it is not innate).
Seeing development this way would account for individual differences in "activity levels, body build and proportion, neural growth, [etc.]...Infants, in a sense, do the best they can with what they have. Nonetheless, because humans also share anatomy and common biomechanical and task constraints, solutions to common motor problems also converge: We all discover walking rather than hopping (although our gait styles are individual and unique)" (p. 91).
Motivation and Developmental Milestones
Another key thing to understand is that your child will develop when he is ready and motivated to do that particular thing (although not denying that there are constraints like being physically strong enough to walk, etc.). If your child has no desire to walk, then he will most likely not put forth the effort required to gain that motor skill. These milestones come about from individual motivation, not from "prespecified genetic instructions" (p. 86). Put another way, "The process is self-organizing because...what is needed to get the process going are only sufficient spontaneous and exploratory movements and some general [motivational value] for the infant...There is no genetic plan" (p. 91).
This is a very different view from the traditional developmental milestones view. Generally, parenting packets, textbooks, websites, etc. will tell you that your child should be doing things by a specific age, but really there is a wide range in individual development as children explore their world and slowly fine tune their movements.
Feel free to leave comments and questions.
Thelen, E. (1995). Motor development: A new synthesis. American Psychologist, 50 (2), 79-95 DOI: 10.1037/0003-066X.50.2.79
Image: Clare Bloomfield / FreeDigitalPhotos.net
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