Welcome to Your Child's Brain: How the Mind Grows From Conception to College (28 page)

The same environment may have different effects on children with different genes.

The development of antisocial behavior is one well-studied example of a feedback loop that starts with child temperament, which affects parental behavior, which then further modifies the child’s behavior. Children who are irritable or prone to aggression are challenging to raise, making them less dandelion-like than most children. Both biological and adoptive parents often respond to the child’s frustrating behavior with harsh restrictions and punishments. Parents who have their own problems with aggression are more likely to produce children of this type—and also more likely to discipline them harshly. In addition, parents who are frustrated for other reasons, such as a troubled marriage or job insecurity, are more likely to respond harshly to their children. This rough treatment in turn increases the child’s aggressive behavior until eventually it may become uncontrollable. Interventions that reduce parental harshness also reduce the risk of future aggressive behavior in the child.

Environmental events that influence child development are not restricted to the family. All children have a life outside the house, and many of their interactions with the world leave permanent traces behind. They spend much of their time with teachers and friends, taking part in sports or other activities. Children learn a lot from their peers. For example, children of immigrants typically speak with the accent of their friends, not their parents, and they learn to speak the language of their peers fluently even if their parents don’t speak it at all. Children’s attitudes and behaviors typically change over time to become more similar to those of their peer group, and this influence can be positive. For example, a low-achieving child who falls in with a group of high-achieving friends is likely to improve his schoolwork. Of course, children choose their friends, rather than being randomly assigned to peer groups (as a researcher might prefer), so much of the similarity between children and their friends results from the selection of friends who are already similar in attitudes and interests. In longitudinal studies, though, children do become more similar to their friends than they were when the friendship started.

MYTH: BIRTH ORDER INFLUENCES PERSONALITY

Firstborn children are self-reliant, traditional, and successful, while last-born children are easygoing, creative, and rebellious? Actually, no. Despite the bottles of ink that have been spilled defending this idea, siblings show no consistent personality differences based on their place in the family. Thousands of psychology papers have been published on this topic—most of them flawed.

One of the biggest flaws is a demographic one. Both small and large families contain firstborn children, while children born third, fourth, fifth, and so on are, by definition, only found in larger families. Many studies failed to control for differences in socioeconomic status between small families (generally well-off and educated) and large families (typically poorer and less educated). So firstborn children, on average, have advantages over later-born children, simply because a larger proportion of the firstborns come from a small family. Many studies that claim to show greater success in firstborn children than in later-born children suffer from this conceptual error.

A second problem arises when researchers ask parents to rate their children’s personalities. Generally, these ratings do not agree with ratings by outside observers. Birth-order effects on personality are perceptible when people are evaluated in the context of their families, but almost nonexistent in the outside world. Part of the difficulty is that parents are necessarily comparing an older child with a younger child, and age is one of the strongest predictors of maturity for any personality type. Parent-rated studies are more likely than those that evaluate personality in other ways to find that firstborn children are more mature than later-born ones. Another concern with this approach is that people act differently within the family than they do outside it, as is clear to any adult who goes home for the holidays and feels instantly reduced to the age of twelve.

In a meta-analysis that only included studies with controls for family size or socioeconomic status, the remaining effects were small and inconsistent. More than half the studies found no effects of birth order on personality at all. And those that did show a pattern were more likely to be small studies, with few subjects, where chance plays a bigger role. This is the opposite of what we would expect for a real effect. By chance, small studies are more likely to be flukes, while large studies have more statistical power and are thus more reliable. The largest study of this topic, with over seven thousand subjects, found no differences in personality between first- and second-born children in families of two children. Sorry, firstborn readers, but there is little credible evidence that birth order influences personality.

Culture strongly influences how temperament develops into adult personality—another example of how brain development matches children’s behavior to their environment. Behavioral inhibition is accepted and encouraged by Chinese mothers, who interpret it as reflecting self-restraint and maturity. In contrast, Canadian mothers endeavor to draw out children who show behavioral inhibition, which in that culture is believed to reflect fearfulness and lack of social skills. Accordingly, high-reactive children in China are more likely than those raised in Western cultures to grow up to be reserved, a trait that leads to social success—in China. In general, the response of a parent to a child’s temperament is more influential if it’s consistent with the beliefs of the culture they live in.

Perhaps personality development is too complicated to study in people, since scientists can’t control (or measure—or perhaps even identify) all of the influences that might matter over people’s long childhood. Indeed, the clearest evidence that parenting influences personality comes from animal studies. Rat mothers who lick and groom their babies a lot produce offspring that are less timid and more prone to exploration. This is true even if the rat pups are born to low-grooming mothers but raised by high-grooming mothers, in the equivalent of human adoption studies. Similar studies show that high-reactive monkeys are more vulnerable than low-reactive ones to variations in the quality of mothering, and as we noted above, some evidence suggests that the same is true of children. (For more details on this research, see
chapter 26
.)

Even if parents cannot entirely control how their children turn out, parenting still matters. First and most important, your relationship with your children is its own reward. How you get along, both as they’re growing up and after they’re adults, depends on how well you care for them. Second, your children’s behavior at home depends a lot on your household rules and how you enforce them (see
chapter 29
). This can have a strong effect on the happiness of their (and your) home life. Third, you can teach your children a wide variety of skills that are useful in adulthood, from cooking to financial literacy to car repair. You can also give them opportunities to discover their passions. Fourth, you can help your child learn strategies to live comfortably and productively with his or her individual temperament, especially if it’s one that you both share.

Think of parenting not as growing the person you want, but as a process of helping your child discover how to make his or her unique abilities and preferences fit well with the rest of the world.

Chapter 18
EMOTIONS IN THE DRIVER’S SEAT

AGES: BIRTH TO EARLY TWENTIES

All of us have experienced emotions that seemed overwhelming and out of control. Imagine feeling that way much of the time, and you have a picture of your young child’s daily experience. One reason that life with toddlers is such a wild ride is that the parts of the nervous system that produce raw emotions mature earlier than the brain regions that interpret and manage them. It’s probably just as well that your children won’t remember that stage of their life. If only we could provide the same service to parents when it’s one of those days.

Emotions organize our minds. As basic survival signals, emotions are present from birth, though they become increasingly more complex as children grow up. At the most fundamental level, emotions (unlike moods) are reactions to the environment that help you to rapidly distinguish between rewarding and threatening aspects of the world. Emotions also compel you to pay attention to salient events, define what you value in life, prepare your body for action, and communicate your internal states to other people.

Certain emotions are universal, occurring in all cultures that have been studied. The facial expressions that signify these so-called basic emotions (fear, joy, disgust, surprise, sadness, and interest) are also built into human biology, so that you could understand whether someone was glad to see you or angry, even if the two of you shared no history, language, or cultural heritage.

Newborn babies can smile, but they do not begin to smile in response to
external events, such as faces, voices, or bouncing, until they are three to eight weeks old. By about three months, they smile more at familiar faces and show interest and surprise. By four months, babies are adept at laughing, and their appreciation for visual games, like peekaboo or seeing funny faces, continues to climb throughout the first year.

Signs of negative emotion are also present early in life. The earliest to appear are startle, disgust, and distress, which (as with smiling) may not be related to external events in the first two or three months. Anger and sadness show up in facial expressions at three months, usually provoked by pain or frustration. All these emotional expressions help to evoke care from parents and other adults.

You may remember the first time your baby smiled back at you. His ability to recognize emotions in other people’s faces develops almost as early as his ability to show facial expressions. By two or three months of age, the occipitotemporal cortical region, which is specialized for face processing, is already activated more by faces than by other objects, though its tuning at this stage is considerably broader than it will be in adulthood. At seven months, infants stare longer at a fearful face than they do at a happy or a neutral face, and their frontal cortex shows an electrical response associated with salient stimuli.

The amygdala sits at the center of the brain’s network for processing emotions (see figure opposite). It receives input from a wide range of brain regions, including information from all your senses. The amygdala’s outputs also go to many brain areas, which constitute two major systems. One, acting via the hypothalamus and brainstem, activates the autonomic nervous system to produce changes in heart rate, blood pressure, and breathing that prepare the body for fight or flight (see
chapter 26
). The other, via various regions of the cortex, controls the cognitive aspects of emotion, including interpretation, regulation, conscious perception, and emotional reactions to memory and imagination. These connections are reciprocal, with both systems influencing the amygdala in return.

Because these connections are so widespread, emotions influence almost every system in the brain. Laboratory studies have shown that emotional signals can improve visual perception, and their fingerprints are all over decision making. Even something as simple as choosing between a blue shirt and a green shirt is difficult for patients with damage to the emotional regions of the cortex.

The amygdala prioritizes speed over accuracy, so it sends out a lot of false alarms. For instance, if you are walking in the woods and see a curved stick on
the ground, you might jump back quickly, fearing a snake, before you have time to realize your error. Such a response is encouraged by a hardwired legacy from our evolutionary history. Often identified with fear, the amygdala actually has a broader mandate: it assigns value to stimuli, priming your brain to react appropriately based on your previous experience with that situation, person, or object. These values can be positive as well as negative, but they’re not very sophisticated. If your visual system isn’t sure whether that dark spot is a spider or a piece of dirt, the amygdala assumes it’s a spider until the cortex corrects that impression.

Even as infants, children show a wide range of individual variability in their tendency to express positive and negative emotions, which is a component of temperament (see
chapter 17
). Some of these differences result from genetics; identical twin infants are more similar than fraternal twins in sociability, inhibition, distress in response to pain, and shyness. The heritability of negative emotionality is particularly high, perhaps reflecting an unusually reactive amygdala. As a result, some children find it more difficult to learn to control their emotions than others do and may need extra help from you in reaching this goal. As we suggested in the previous chapter, the effects of your parenting may also be exaggerated in children like this (see also
chapter 26
).