All this reflects how infants actually develop: Babies take different routes to the same destination. There's no right way to learn to walk, for example, and there's scarcely even a right time: The accurate range for when babies should start extends from 8 months to almost 20 months—an amazingly, almost meaninglessly broad stretch of time. The most interesting research on motor development in recent years treats it as the product of many different systems: the infant's environment, personality, nervous system, and personal physical limitations. When all these variables interact, you get a lot of different results, as countless studies have made clear. You don't get a chart that looks like something out of The Ascent of Man.
But the idea of the typical child is ever with us, never mind the volumes of research disproving it. As several prominent developmental psychologists have written, somewhat despairingly, "Ages and stages so thoroughly pervade our conception of motor development that every pediatrician's office and developmental textbook sports a requisite table of developmental norms." These charts and tables make us anxious and shrink our sense of the possibilities of infancy. There's no chart that can make sense of this photo of an 11-month-old Efe infant, in a rainforest in the Democratic Republic of Congo, carefully cutting a fruit in a half with a machete.
Of course, parents want some sense of what their children should be doing, and knowing that their baby girls technically might be able to use a machete won't help much. But false milestones and misleading developmental narratives aren't helping, either. It's a sorry state of affairs: Even as developmental psychologists have discarded the idea of universal developmental milestones, those milestones are the only things many parents know about developmental psychology.
We should start by erasing the word normal from the developmental vocabulary: What's typical in infancy is variation. Rather than a multitude of milestones, parents would sleep better with fewer but more relevant guidelines, an acknowledgement of how unstructured infancy actually is. At our pediatrician's office, I recently discovered a rare such example: a CDC flyer with the heading, "It's time to change how we view a child's growth." It lists a few key achievements for the end of each year, helping parents sift out actual problems. If a baby doesn't respond to "no" at the age of 1, for example—even if "responding to" just means ignoring—that's probably worth mentioning to the pediatrician.
I can report that Isaiah, who has always lagged behind his mythical normal counterpart, has met all the milestones on the CDC's short list. As a proud parent, though, I'm a little aggrieved it fails to recognize his deep talent for apple taxonomy: He's clearly way ahead of his peers.