Theme 1: Nature and Nurture: All Interactions, All the Time

When people think of a child’s nature, they typically focus on the biological characteristics with which the child enters the world. When they think of the child’s nurture, they focus on the child-rearing experiences provided by parents, caregivers, and other adults. Within this view, nurture is like a sculptor, shaping the raw material provided by the child’s nature into closer and closer approximations of its final form.

Although this metaphor is appealing, the reality is much more complex. Unlike the sculptor’s passive media of marble and clay, children are active participants in their own development. They seek out their own experiences, based on their inclinations and interests. They also influence other people’s behavior toward them: from birth onward, their nature influences the nurture they receive. In addition, rather than nature doing its work before birth and nurture doing its work after, nurture influences development even before birth, and nature is just as influential in adolescence and adulthood as earlier. In this section, we review how nature and nurture interact to produce development.

Nature and Nurture Begin Interacting Before Birth

When prenatal development proceeds normally, it is easy to think of it as a simple unfolding of innate potential, one in which the environment matters little. When things go wrong, however, the interaction of nature and nurture is all too evident. Consider the effects of teratogens. Prenatal exposure to these potentially harmful substances—which include toxins in the general environment, such as mercury, radiation, and air pollution, as well as toxins that depend on parental behavior, such as cigarettes, alcohol, and illegal drugs—can cause a wide variety of physical and cognitive impairments. However, whether a given baby will actually be affected depends on innumerable interactions among the genetics of the mother, the genetics of the fetus, and a host of environmental factors such as the particular teratogen and the timing and amount of exposure.

The interaction of nature and nurture during the prenatal period is also evident in fetal learning. The experience of hearing their mother’s voice while in the womb leads newborns to prefer her voice to that of other women once they enter the world. Fetuses can also learn taste preferences from their mother’s diet during pregnancy. Thus, even qualities that are present at birth, which are often thought of as being determined purely by nature, reflect the fetus’s experience as well.

Infants’ Nature Elicits Nurture

Infants’ expressions of contentment and happiness when engaging in certain activities motivate their parents and other adults to engage in the activities with them.

EMMANUEL FAURE/GETTY IMAGES

Nature equips babies with a host of qualities that elicit appropriate nurture from parents and other caregivers. One big factor in babies’ favor is that they are cute; most people enjoy watching and interacting with them. Their looking and smiling at other people motivates others to feel warmly toward them and to care for them. Their emotional expressions—cries, coos, and smiles—guide caregivers’ efforts to figure out what to do to make them happy and comfortable. In addition, their attentiveness to sights and sounds that they find interesting encourages others to talk to them and to provide the stimulation necessary for learning. One simple example of this interactive relationship is the fact that parents everywhere sing to their infants; infants throughout the world find singing soothing, bounce in response to rhythm, and respond positively to melodies.

Timing Matters

The effects of an experience on development depend on the state of the organism at the time of the experience. As already noted, timing of exposure to teratogens greatly influences their effects on prenatal development. For example, if a pregnant woman comes down with rubella early in pregnancy, when the developing visual and auditory systems are at a particularly sensitive point, her baby may be born deaf or blind; if she comes down with rubella later in pregnancy, no damage will occur.

Timing also influences many aspects of development in the months and years following birth. The development of perceptual capabilities presents numerous illustrations of the importance of appropriate experience at the appropriate time. The general rule in such cases is “use it or lose it”: for normal development to occur, children must encounter the relevant experiences during a certain window of time.

Auditory development provides a good example. Until 8 months of age, infants can discriminate between phonemes regardless of whether they occur in the language the infants hear daily. By age 12 months, however, infants lose the ability to hear the difference between similar sounds that they do not ordinarily encounter or that are not meaningfully different in their native language.

Similar sensitive periods occur in grammatical development. Children from East Asia who move to the United States and begin to learn English as a second language before age 7 acquire grammatical competence in English that eventually matches that of native-born American children. Those who arrive between ages 7 and 11 learn almost as well. However, individuals who immigrate at later ages rarely gain comparable mastery of English grammar, even after many years of hearing and speaking the language of their adopted land. Deaf children’s learning of American Sign Language shows a similar pattern: early exposure results in more complete grammatical mastery.

The importance of normal early experience is also evident in social, emotional, and intellectual development. Infants and toddlers who do not have an emotional connection with any caregiver, such as the children who spent their first years in the infamous orphanages of Romania in the 1980s or in concentration camps during World War II, often continue to interact abnormally with other people after being placed in loving homes. Those who spent their first two years or more in the Romanian orphanages also had unusually high rates of low IQ for many years after they were adopted into loving homes in Great Britain. Thus, in many aspects of the development of perception, language, intelligence, emotions, and social behavior, the timing of experience is crucial: normal early experience is vital for successful later development.

Nature Does Not Reveal Itself All at Once

Differences in running speeds are partially attributable to genetic differences that are present at birth, but nature takes time to reveal itself. Who could have looked at these children when they were newborns and predicted which would be the best runners?

POLKA DOT IMAGES/THINKSTOCK

Many genetically influenced properties do not become evident until middle childhood, adolescence, or adulthood. One obvious example is the physical changes that occur at puberty. A less obvious example involves nearsightedness. Many children are born with genes that predispose them to become nearsighted, but most do not become so until late childhood or early adolescence. The more close work, including reading, they do during childhood, the more likely that the genetic predisposition will eventually be realized. A third example involves children who are born with certain types of brain damage. These children’s performance on IQ tests is comparable to that of other children through age 6 years, but falls considerably behind thereafter.

The development of schizophrenia follows a similar path. Schizophrenia is highly influenced by genes inherited at conception, but most people who become schizophrenic do not do so until late adolescence or early adulthood. As with other aspects of development, the emergence of schizophrenia reflects a complex interplay between nature and nurture. Children with a schizophrenic biological parent who are raised by nonschizophrenic parents are more likely to become schizophrenic themselves than are the biological children of the nonschizophrenic parents. Children who are raised in troubled homes are also more likely than others to become schizophrenic. However, the only children with a substantial likelihood of becoming schizophrenic are those who have a biological parent who is schizophrenic and who also grew up in a troubled family. As in other contexts, the interaction between the children’s nature and the nurture they receive is crucial.

Perhaps the most surprising and compelling evidence for the interaction of nature and nurture comes from the emerging field of epigenetics. Although people often think of the genotype as being “fixed” at birth, experience can enhance or silence gene expression. Early stressful environments, such as those imposed by poverty, seem to especially influence later gene expression. Thus, adults who grew up in low-income families exhibit different patterns of gene expression decades later than do adults who grew up in high-income homes, regardless of their incomes as adults. Even more remarkably, some of these effects of the early environment on the genome are passed down to the next generation. Thus, not only does nature not reveal itself all at once, but nature itself changes as a result of nurture.

Everything Influences Everything

One common reaction to learning about the complex interactions between nature and nurture is “It sounds like everything influences everything else.” This reaction is basically accurate. Consider some of the factors that influence children’s and adolescents’ self-esteem. Genes matter; the closer the biological relation between two children or adolescents, the more similar their degree of self-esteem is likely to be. A large part of the reason for this genetic influence on self-esteem is that genes influence a wide range of other characteristics that themselves influence self-esteem. For example, genes strongly affect attractiveness, athletic talent, and academic success, all of which contribute to self-esteem.

Factors other than genes also play large roles in the development of self-esteem. Support from one’s family and peers contribute in a positive way; poverty and unpopularity contribute in a negative way. Unrelated adults also can have positive or negative influences on self-esteem; for example, having a teacher who is supportive can promote a child’s self-esteem; conversely, having a teacher who is hostile or demeaning can reduce it. Values of the broader society also are influential. East Asian societies tend to emphasize the importance of self-criticism, and children and adolescents in those societies report lower levels of self-esteem than do peers in Western societies.

Complex interactions are not limited to the development of self-esteem or to social development; they are characteristic of development in all areas. For example, in the development of intelligence, the influence of genetics seems to be greater than that of shared environment for children from middle- and upper-income backgrounds, but the opposite is true for children from impoverished backgrounds. Similarly, parental involvement in school is more closely related to academic achievement in low-income families than in more affluent families. Thus, children’s nature—their genes, personal characteristics, and behavioral tendencies—interact with the nurture they receive from parents, teachers, peers, the broader society, and the physical environment in ways that shape their self-esteem, intellect, and other qualities.