Childhood

The period between birth and adulthood, during which a person develops physically, intellectually, and socially.

History of childhood

Childhood has been defined differently across the ages. The Greek philosopher Plato (427?-347 B.C.) believed children were born with certain dispositions that could be changed by their environment. Ancient Romans expressed great affection for their children in letters and on tombstones. During the Middle Ages, little distinction was made between adults and children, who worked from a very young age. The Renaissance saw the beginning of the nuclear family in Europe, with an increased focus on childhood as a time for education and training. John Locke (1632-1704), founder of the empirical school of philosophy, believed the child enters the world as a tabula rasa or blank slate, and learns through experience. Jean-Jacques Rousseau (1712-1778) took the opposite tack, recommending that education should follow nature since infants automatically prefer goodness. According to Sigmund Freud's (1856-1939) psychoanalytic theory, children must pass through five psychosexual stages to achieve healthy adulthood. In contrast behaviorist John Watson (1878-1935) asserted that, given a controlled environment, he could train a child to be anything from doctor to thief. The emphasis on environment, particularly the behavior of parents, continued through the twentieth century until studies of identical and fraternal twins, reared together or apart, began to show the effect of genes on the journey from infancy to adulthood.

Prenatal development

The future adult begins not at birth but at conception, with the creation of a unique set of genes, half from the mother, half from the father. This genetic blueprint is called the genotype; its outward manifestation is the phenotype. Sometimes the phenotype is controlled directly by the genotype, for example, eye color. More often, the phenotype represents the interaction of the genotype and the environment. It is even possible for the genotype to be altered by the environment, as happens when men exposed to certain toxins suffer an increased risk of fathering children with genetic abnormalities.

Fewer than half of fertilized eggs, called zygotes, survive the first two weeks during which the zygote moves from the fallopian tube where it was fertilized to the uterus where it is implanted. During the next six weeks, the zygote differentiates into an embryo with internal organs, skin, nerves, and rudimentary limbs, fingers, and toes. In the final seven months of gestation, the maturing skeletal, muscular, and nervous systems of what is now called the fetus make movement possible. Babies born at 28 weeks can survive, although often with chronic health problems.

As each system undergoes its most rapid growth, it is especially vulnerable to damage. In addition to genetic abnormalities like Down syndrome, environmental agents called teratogens can affect the fetus. These might be maternal viruses such as rubella (German measles) or chemicals such as nicotine, alcohol, and cocaine. Exposure to nicotine is linked to premature birth, low birth weight, and cleft (malformed) palate and lips, while exposure to alcohol is linked to intellectual and behavioral impairments. An inadequate maternal diet also puts the fetus at risk, especially its brain and nervous system. Prenatal teratogens can cause lifelong problems or even death. The vast majority of babies, however, are born healthy and normal.

Infancy

Newborns enter the world with many skills. In addition to a range of adaptive reflexes such as grasping, sucking, and rooting (turning the head when the cheek is touched), they are able to recognize their mothers' face, voice, and smell. Even more impressive, less than one hour after birth, babies can imitate gestures such as sticking out the tongue.

Physical development

The average healthy newborn is 7.5 pounds (3.4 kg) and 20 inches (52 cm). It triples its weight and grows 10 to 12 inches (24-30 cm) its first year. By age two for girls and two-and-a-half for boys, babies reach half their adult height. Physical development is largely programmed by a genetically determined timetable called maturation, which proceeds in predictable stages. For healthy, well-nourished babies, progress is influenced only slightly by environment, although they need opportunities to practice new skills.

The rate of physical growth slows after the second year, not accelerating again until puberty. Both size and rate of growth are genetically determined. In industrialized societies, puberty begins at 10 for girls and 12 for boys, ages that have declined significantly over the past 150 years due to improved health and nutrition.

Intellectual development

The Swiss researcher Jean Piaget (1896-1980) pioneered the field of cognitive, or intellectual, development. On the basis of his observations and ingenious questions, he divided children's thinking into four qualitatively distinct stages, moving from a direct sensory understanding of the world, to the symbolic representation of objects, to mental manipulation of objects, to logical thinking about abstract concepts. Using new techniques such as changes in sucking and heart-rate, contemporary researchers have found that, contrary to Piaget's theory, even babies seem to understand basic principles like object permanence, the concept that objects continue to exist when hidden. And although his middle stages of development have been confirmed, far fewer people attain Piaget's final stage of logical reasoning than he predicted.

Other theories of learning attribute cognitive development not to the child's own construction of knowledge, but to conditioning, the effect of environment on the child. Conditioning works by encouraging behavior through reinforcement or discouraging it through punishment. Social learning theory adds another mechanism, modeling, or learning by observation.

Intelligence

The measurement of intelligence, psychometrics, began with Sir Francis Galton (1822-1911). Although his measures of vision, reaction time, and grip strength proved poor predictors of academic success, his model of multiple indicators of intelligence has remained useful. IQ, or intelligence quotient, was originally a way to identify children who needed remedial teaching. It compares mental age to chronological age, with average intelligence set at 100. Modern IQ tests are quite successful in predicting school success, but have been criticized as culturally biased and limited in scope. IQ tends to remain the same when measured after the age of 4, an indication of its reliability.

Language learning

Perhaps the most crucial task of childhood is learning to communicate. Researchers have found that humans are attuned to language even before birth. Following a universal sequence, even deaf babies first cry, then coo, then babble. Around eight months, babies begin to copy the sounds and intonations of their native language and speak their first words around one year of age. Vocabulary expands to over 200 words by age two, expressed in phrases such as "want cookie." The speech of three-year-olds reflects knowledge of plurals, past tense, negatives, and questions, along with an increased vocabulary. Grammatical complexity and vocabulary continue to expand throughout the school years. Children who are spoken and read to more are linguistically advanced, although late talkers tend to catch up with early talkers in the absence of other problems. Children who are read to also have less trouble learning to read.

Personality development

Personality is what makes each person unique. Where do individual differences come from and how stable are they from birth to adulthood? There is strong evidence for a biological component to personality dimensions like sociability, irritability, neuroticism, and conscientiousness, but environmental effects are also present. A baby's innate sociability, for example, can be squelched by a depressed mother, or a child's innate irritability increased by a punitive teacher. In general, however, personality characteristics remain stable from infancy to adolescence.

Social development

Children grow up in a web of social relationships. The first and most important is the bond between infant and mother called attachment. Attachment is crucial because securely attached babies tend to become sociable, confident, independent, and emotionally mature children. Adolescents who feel close to their parents also enjoy more friendships and higher self-esteem. Another predictor of social success is physical attractiveness. Even infants prefer attractive faces, as do older children. Boys who physically mature early are also more popular. Not surprisingly, aggressive, disruptive, and uncooperative behaviors are predictors of social rejection. A cycle of aggression and rejection often persists into adulthood.

Nature and nurture

The most contentious issue in the study of childhood is the relative importance of genetics (nature) and environment (nurture). Purely environmental models such as behaviorism have been contradicted by numerous studies showing a strong genetic influence for everything from intelligence to shyness to sexual orientation. On the other hand, even clearly genetic traits interact with environment. Tall children, for example, are often treated as more mature. Intelligence is even more complicated. Twin studies show that between 50 and 60 percent of IQ is determined by genes. A child's genetic intellectual potential, then, is actually a range that can be maximized by a rich environment or minimized by a deprived one. In general, a child's development follows a genetic blueprint, but the final result is constrained by the building materials of the environment.

Cultural differences

Most research on childhood is conducted in Western, industrial cultures. However, there is a growing body of cross-cultural studies highlighting both similarities and differences in childhood around the world. Secure maternal attachment, for example, is less common in Germany, a culture that values autonomy, than in Japan, a culture that values community. Guatemalan mothers always sleep with their babies, who fall asleep without the rituals and problems typical among American babies. Attitudes toward school achievement also vary. Japanese and Chinese mothers expect more from their children than do American mothers, and their children outperform Americans. Some children spend their first years in constant proximity to their mother, some in day care centers. Some children watch younger siblings or work in factories, some attend school. Some children live in extended families, an increasing number live with a single parent. Despite these differences, however, children everywhere show a zest for learning, play, and friendship, and a drive to make sense out of their ever changing world.