Physical movement by a newborn is jerky and uncoordinated, yet by the end of the first year of life, an infant has coordinated his or her motor ability to be able to go where he or she wants to. In the course of a year, rapid changes and complicated developmental progression lead to the explorative one-year-old.
One of the hallmarks of infancy is a collection of neonatal reflexes. These are innate, fixed patterns of action that occur in response to stimuli – and all babies have them. In fact, the presence and strength of a reflex is an indicator of the maturing of the central nervous system. Weak or non-present reflexes can reflect an immature or damaged central nervous system or even a broken bone. Reflexes get stronger across prenatal development, which means that premature babies often show weaker reflexes than full-term babies. Note that this difference generally goes away when you compare premature and full-term babies by gestational age (i.e., a baby born ten weeks early at 30 weeks has very different reflexes than a baby born at 40 weeks, but when the premature baby is 10 weeks old, that baby has similar reflexes to a newborn baby born at 40 weeks).
Some neonatal reflexes are clearly important. The rooting reflex is when infants turn their face towards a touch on the check and open their mouth. This reflex serves a clear purpose for breastfeeding (and can be useful for helping a baby bottle feed). Stroking a cheek with a breast or hand will causes the baby to turn and to latch onto their milk source. Oral contact with a nipple causes the sucking reflex, which is followed by a swallowing reflex. These two reflexes, combined with the rooting reflex, make it more likely for a newborn to get nutrition.
It’s less easy to understand the importance of a few other reflexes. For example, the tonic neck reflex is when an infant turns its head, the arm on that side of the body extends while the arm and knee on the other side flex up. Some have argued this will keep the hand in the babies eyesight – who knows. A second reflex is the stepping reflex – when a baby is held up and feet are gently touching a surface, the baby will step his or her feet (Note: This will entertain siblings and grandparents for hours). My personal favorite neonatal reflex is the moro reflex, which is when a startled baby will jerk their arms out into a high- v shape and then wrap arms back into their chest. It is frequently accompanied by crying, which is less adorable than the other two parts. It is thought that the moro reflex is an attempt by an infant to gain stability by reaching out and grabbing back in when falling (think about monkeys falling off a mom’s back).
Generally speaking, these reflexes fade as infants age, with most of these reflexes gone by 5 to 6 months of life. Other reflexes will be lifelong, like blinking, coughing, and sneezing.
Beyond reflexes, developing motor skills follow a typical progression. What follows is the typical advancement of motor skills, but note that the age ranges refer to North American babies (more on cultural variations in movement in a few paragraphs):
1. Prone, lifting head (First month of life)
2. Prone, lifting up using cobra support (think cobra pose in yoga) (2-4 months)
3. Rolls over (2 to 5 months)
4. Supporting some weight with legs (think of a very unflexible person’s downward dog) (3-6 months)
5. Sitting without support (5-8 months)
6. Standing with support (5-10 months)
7. Pulling self to stand (6-10 months)
8. Walking while holding onto something (sometimes called cruising) (7-12 months)
9. Standing alone (9-14 months)
10. Walking alone (11 to 14 months)
90% of you totally skipped reading that list, so let me tell you what is important about it: it does not list crawling. That’s right. The old adage, “You have to learn to crawl before you learn to walk,” is absolute bullshit. Really, the phrase should be, “You have to sit before you can walk.” But I admit it does sound less sexy.
In actuality, probably the most incredible motor milestone in this entire list – the most transformative – is sitting. Strange that the activity that adults worry about doing too much of is probably the most important milestone of typical infant motor development. Why? Well first, it strengthens muscles that will eventually allow for upright walking. But second, it frees up arms and hands for reaching into the environment, which facilitates cognitive development.
There is a lot of variability in the timing achievement of these motor milestones. Culturally, there is huge variation in how quickly infants progress through these milestones. For example, a relatively recent study found that in urban China, infants are placed on beds and surrounded by pillows to keep them from crawling on the floor, which means it takes them longer to develop the muscular strength to support their upper body weight, meaning later sitting, crawling, and walking. Contrast that with a different cultures like some groups from Kenya, West Africa, and East Indies which actively encourage motor development through facilitated sitting, massage, and manipulation, which lead to faster achievement of these milestones.
Beyond cultural differences in encouraging motor development, it is also true that societal trends and transitions can affect motor development. A great example is the impact of the “Back to Sleep” campaign on motor development. In the late 1990s, data began to suggest that children were crawling later or not crawling at all (simply progressing from sitting to walking). This change seems to be attributable to the campaign to get parents to sleep their babies on their backs. This public health outreach to sleep children on backs was done to encourage back sleeping, which is associated with a lower rate of Sudden Infant Death Syndrome. However, this means that babies spend less time in the prone position (stomach sleeping) and so muscle strength of the back and ability to lift the upper body is delayed. Moreover, the number of toys made for children to lie on their back (think of play mats and crib mobiles) means that kids are less motivated to roll over or to wiggle forward on one’s belly to learn to crawl. All they have to do is lie there and enjoy looking at mobiles and mirrors.
Don’t fret though. There is no evidence that this delay or absence of crawling has any negative effects on kids. Indeed, while my first child never crawled, my second wrecked havoc from 7 months on – but both are on point with their age appropriate motor milestones years later. Current norms and best practice for children in one domain, such as sleep practices, can affect child development in another area, such as motor development.