Welcome to Your Child's Brain: How the Mind Grows From Conception to College (7 page)

A recent study suggests that as many as one in fifteen induced deliveries between thirty-four and thirty-seven weeks are done without a compelling medical reason. Examples include hypertension or a complication in a prior pregnancy, neither of which is considered an absolute indication for early induction. In these cases, early delivery should be weighed against the risks we have described. Of course, in many cases, such as bleeding or a prolapsed umbilical cord, the necessity is unavoidable.

Therefore one of the best things you can do to protect your baby’s growing brain is to allow your pregnancy to run its full course whenever possible. Between 10 and 20 percent of all U.S. deliveries are induced, and roughly half of these inductions are elective (not medically necessary). Reasons for elective induction include doctor or patient convenience and doctors’ concerns about legal liability. We recommend following the American College of Obstetricians and Gynecologists recommendation that elective induction should not be scheduled before week thirty-nine of pregnancy (this cutoff is set late because the exact stage of pregnancy is not always known with precision) unless there is a clear medical need. To use a baking metaphor, that bun in the oven will turn out great—if you wait until it’s done.

Chapter 3
BABY, YOU WERE BORN TO LEARN

AGES: BIRTH TO TWO YEARS

No wonder babies sleep so much. They’ve got a lot of hard work ahead of them. Infants come equipped with a basic toolkit for learning, as we described in
chapter 1
. But that still leaves a lot of items on their to-do list. In the first year of life, babies must lay the foundations for all their adult abilities, from language to locomotion. Their brains are changing more quickly at this age than they ever will again. Many of those changes help babies to learn about the specific environment into which they have been born.

People can live in an astounding variety of places, from the frozen tundra to the sweltering desert, and in a vast array of social systems as well. Growing up in New York City or Barcelona is a very different experience from growing up in a subsistence village in the Amazon, but babies come into both of those situations with nearly all the same genes.

Unlike many animals, people are not hardwired to be a good fit to their environment at birth. Instead, babies arrive equipped with the skills required to adapt flexibly to a wide range of conditions, an ability that has allowed people to survive all over the world. The benefits of that approach are enormous, and so are the costs: children need a lot of care for a long time before they become independent. This high-risk, high-reward reproductive strategy affects the shape of most people’s lives for decades, first as children and then as parents.

Babies are driven to explore and test their ideas about the world—which is why they seem to be getting into things all the time—and they love making things happen. When a baby learns to push a bowl from her high chair to make a crashing mess, you can see the glee as she triumphantly proceeds to do it again and again. Being effective in the world is enormously rewarding for children and adults alike. Infants, though, sometimes get confused about how they caused something to happen, so you can see them trying to coax an object into behaving by talking to it. This confusion between physical and psychological causality usually disappears by the first birthday.

Just as babies have been shaped by evolution to be supereffective learners, adults have become equally effective teachers. It may look like a game of peekaboo, but there’s serious stuff going on here. Babies are extremely good at getting what they need from their adult caregivers—not only food and shelter, but also information and examples. As a mother coos to her baby that he’s such a good boy, he is learning about language, relationships, and much more.

MYTH: BREAST-FEEDING INCREASES INTELLIGENCE

Everyone seems sure that giving breast milk to babies will make them smarter. We thought so ourselves when we started writing this book, but our careful examination of the scientific literature shows that the evidence for this idea is questionable.

There’s no doubt that children who were fed exclusively on breast milk during infancy have higher intelligence on average than children who were not breast-fed. The important question is why this correlation occurs. One possibility is that this difference has something to do with the characteristics of breast-feeding mothers.

Indeed, women who choose to breast-feed their babies differ in many relevant ways from women who don’t breast-feed. Compared to women who bottle-feed their children, women who breast-feed have higher IQs, are more educated, are less likely to be poor, and are less likely to smoke. An increase of about fifteen points (one standard deviation) in the mother’s IQ more than doubles her likelihood of breast-feeding her baby. Headlines reading “Smart Mothers Found to Have Smart Babies” probably wouldn’t be so memorable.

Researchers have tried to deal with these confounding factors in a variety of ways. Meta-analysis, a powerful statistical technique for combining the findings of multiple studies to increase our confidence in the conclusions, has produced inconsistent results. Some papers report a small effect of breast-feeding on IQ, and others find no effect. In general, though, studies with a large number of subjects have tended to find smaller effects. To a scientific reader, this is not encouraging news. Real effects (not due to chance) should be easier to see in large populations. One meta-analysis concluded that higher-quality studies were also less likely to find an effect of breast-feeding on intelligence.

In one large study, the IQ differences associated with breast-feeding were completely eliminated by taking the mothers’ characteristics into account. Among the 332 pairs of siblings in which one was breast-fed and the other was bottle-fed, there was no difference in IQ. Another study of 288 sibling pairs in which only one child was breast-fed reported similar findings.

The ideal way to address these concerns would be to assign some infants to be breast-fed and others to be bottle-fed. One large study in Belarus came as close as ethically possible by randomly assigning some mothers to a support program that increased the duration of successful breast-feeding. The authors reported that the support program substantially increased children’s IQs at age six. Unfortunately, their IQs were tested by pediatricians who had a stake in the program’s success and did not normally administer IQ tests. Indeed, when psychologists retested some of the children, their scores were significantly lower, raising the possibility of bias in the initial measurements and causing considerable uncertainty about the true size of the effects.

Our reading of the literature is that the weight of the evidence suggests that breast-feeding has little or no influence on a baby’s later intelligence. Of course, we’re not arguing against breast-feeding, which has many other benefits, including the opportunity for loving physical contact with your baby (see
chapter 11
). But mothers who are unable to breast-feed should not worry that they are harming their baby’s intellectual development.

Because of the brain talents we discussed in
chapter 1
, even newborns are not passive recipients of adult instruction. Instead babies actively seek out the information that is most useful to them at a particular stage of development, and their behavior reliably elicits the kind of help that they need from adults. For instance, many people speak to babies in
motherese
—a high-pitched, sing-song, and slow version of regular language with elongated vowel sounds. Babies prefer to hear motherese and interact more intensely with people who speak this way, as most adults and older children do instinctively. It is probably not a coincidence that the properties of motherese, including clear pronunciation and pauses between words, are also very well suited for helping babies learn about language.

Of course these interactions with adults influence some aspects of how babies develop, such as determining which language the baby learns. All normal babies eventually learn the things they need to know, but the rates and details of learning depend on the experience of growing up in a particular culture. For example, there are a lot of cross-cultural variations in timing and even occurrence of the stages of motor development that pediatricians use to determine whether your child is progressing normally (see
Practical tip: Guided practice can accelerate motor development
). In the U.S., learning to crawl is widely considered a prerequisite for learning to walk, but it is merely one of many ways to get around that infants may discover. Almost a third of babies in Jamaica do not crawl at all, and the rest begin to crawl at the same age as first walking, around ten months. Similarly, 17 percent of British infants never crawl, and a hundred years ago, 40 percent of U.S. infants did not learn to crawl, probably because babies in that era wore long gowns that made crawling difficult.

PRACTICAL TIP: GUIDED PRACTICE CAN ACCELERATE MOTOR DEVELOPMENT

Infants learn to hold their heads up, sit, and walk months earlier in cultures that provide a lot of tactile stimulation and help babies to practice motor skills. In African, Caribbean, and Indian cultures, mothers massage and stretch infants after bathing them. These routines can include swinging infants around or tossing them in the air. Babies carried in a sling improve muscle strength and coordination as they adjust to Mom’s movements. Laboratory studies verify that such stimulation promotes motor development. Spinning an infant in an office chair twenty times twice a week over four weeks (a safe and fun way to provide stimulation) or moving the legs passively (twenty minutes daily for eight weeks) speeds the infant’s acquisition of motor skills.

To teach sitting, some African and Caribbean mothers hold young infants in the sitting position on their laps or prop them up with a cushion or other support. To promote walking, mothers hold infants in a standing position and bounce them up and down, causing them to make stepping movements. Once babies are able to hold themselves up, mothers encourage the babies to take steps while leaning against furniture, sometimes luring them with food. In such cultures, even young babies spend much of their time in sitting or standing positions. Western parents take such a deliberately planned approach only when teaching their toddlers how to climb stairs.

Trained infants develop motor skills more quickly than untrained infants, but only the skills that are specifically practiced. Laboratory studies verify that babies who practice crawling movements start to crawl earlier, and babies who practice stepping start to walk earlier. In contrast, babies are slower to develop motor skills if their movements are restricted. Denver babies born in winter start to crawl the following summer three weeks younger than summer-born babies who learn to crawl in the winter, apparently because cold weather limits the latter group’s opportunities to practice.