CHAPTER 3
Child Development
Theme: The principles of development help us better understand not only children, but our own behavior as well.
Preview
A Star Is Born—Here’s Amy!
Olivia has just given birth to her first child, Amy. Frankly, Amy looks something like a pink prune, with pudgy arms, stubby legs, and lots of wrinkles. She also has the face of an angel—at least in her parents’ eyes. As Olivia and her husband Tom look at Amy, they wonder, “How will her life unfold? What kind of a person will she be?” What if we could skip ahead through Amy’s childhood and observe her at various ages? What could we learn?
Seeing the world through her eyes would be fascinating and instructive. A child’s viewpoint can make us more aware of things we take for granted. For example, younger children are very literal in their use of language.When she was 3,Amy thought her bath was too hot and said to Tom, “Make it warmer, daddy.” At first, Tom was confused. The bath was already fairly hot. But then he realized that what she really meant was, “Bring the water closer to the temperature we call warm.” It makes perfect sense if you look at it that way.
Today we can merely guess about Amy’s future. However, psychologists have studied many thousands of children.
Their findings tell a captivating story about human growth and development. Let’s let Olivia, Tom, and Amy represent parents and children everywhere, as we see what psychology can tell us about the challenges of growing up.
Tracing Amy’s development might even help you answer the question, How did I become the person I am today?
¡ You are a product of your genetic heritage and the environments in which you have lived.
¡ Infant development is strongly influenced by heredity.
However, environmental factors such as nutrition, parenting, and learning are also important.
¡ All areas of child development are affected by conditions of deprivation and enrichment.
¡ Forming an emotional bond with a caregiver is a crucial event during infancy.
¡ Learning language is a cornerstone of early intellectual development.
¡ Piaget’s stage theory provides a valuable map of how thinking abilities unfold.
¡ Vygotsky’s theory reminds us that a child’s mind is shaped by human relationships.
¡ Effective child discipline is consistent, humane, and encouraging and is based on respectful communication.
¡ Genetic research is making it possible to control some hereditary aspects of human reproduction, development, and behavior.
Gateways to Child Development
How do heredity and environment affect development?
What can newborn babies do?
What influence does maturation have on early development?
Of what significance is a child’s emotional bond with parents?
How important are parenting styles?
How do children acquire language?
How do children learn to think?
How do effective parents discipline their children?
How has new knowledge about genetics affected parenthood?
Key Questions
Heredity and Environment— The Nurture of Nature
Children are the heart of developmental psychology (the study of progressive changes in behavior and abilities). However, be aware that human development involves every stage of life, from conception to death (or “the womb to the tomb”). Some events in life, such as achieving sexual maturity, are mostly governed by heredity. Others, such as learning to swim or use a computer, are primarily a matter of environment. But which is more important, heredity or environment? Let’s consider some evidence on both sides of the nature-nurture debate.
Heredity
Heredity (“nature”) refers to the genetic transmission of physical and psychological characteristics from parents to their children.
An incredible number of personal features are set at conception, when a sperm and an ovum (egg) unite.
How does heredity operate? The nucleus of every human cell contains 46 chromosomes. (The word chromosome means “colored body.”) These tiny thread-like structures hold the coded instructions of heredity (œFig. 3.1). A notable exception is sperm cells and ova, which contain only 23 chromosomes.
Thus, Amy received 23 chromosomes from Olivia and 23 from Tom. This is her genetic heritage. Chromosomes are made up of
DNA, deoxyribonucleic (dee-OX-see-RYE-bo-new-KLEE-ik) acid. DNA is a long, ladder-like chain of chemical molecules (œFig. 3.2). The order of these molecules, or organic bases, acts as a code for genetic information.
Developmental psychology The study of progressive changes in behavior and abilities from conception to death.
Heredity (“nature”) The transmission of physical and psychological characteristics from parents to offspring through genes.
Chromosomes Thread-like “colored bodies” in the nucleus of each cell that are made up of DNA.
DNA Deoxyribonucleic acid, a molecular structure that contains coded genetic information.
œ Figure 3.1 This image, made with a scanning electron microscope, shows several pairs of human chromosomes. (Colors are artificial.)
© Biophoto Associates/Science Source/Photo Researchers
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The DNA in each cell contains 3 billion base pairs. That’s enough to record all the instructions needed to make a human—with room left over to spare. Amazingly, the DNA of everyone who has ever lived is 99.9 percent the same. Genetically, the difference between you and Michael Jordan, Albert Einstein, Rosa Parks, Princess Diana, or Saddam Hussein is based on only about 1 of every 1000 base pairs. However, the crucial pairs can occur in endless combinations, which explains the rich diversity of humanity (Hamer & Copeland, 1998).
Genes are small areas of the DNA code. Each of the 40,000 genes in your cells affects a particular process or personal feature.
Sometimes, a single gene is responsible for an inherited trait, such as Amy’s eye color.Most characteristics, however, are
polygenic (pol-ih-JEN-ik), or controlled by many genes working in combination.
Genes may be dominant or recessive.When a gene is dominant,
the feature it controls will appear every time the gene is present.When a gene is recessive, it must be paired with a second recessive gene before its effect will be expressed. For example, if Amy got a blue-eye gene from Tom and a brown-eye gene from Olivia, Amy will be brown-eyed, because brown-eye genes are dominant.
If brown-eye genes are dominant, why do two brown-eyed parents sometimes have a blue-eyed child? If each parent has two brown-eye genes, the couple’s children can only be brown-eyed.
But what if each parent has one brown-eye gene and one blueeye gene? In that case the parents would both have brown eyes.
Yet, there is 1 chance in 4 that their children will get two blueeye genes and have blue eyes (œFig. 3.3). Along the same lines, genetics can sometimes be used to predict the chances that a child will be born with various inherited problems. (See A Step Beyond later in this chapter for more information.)
Genetic Programming
Heredity influences events from conception to senescence (seh- NESS-ens: aging) and death (see ¡Table 3.1). That’s why the
human growth sequence, or overall pattern of physical development, is universal. Heredity also determines eye color, skin
Sugar-phosphate backbone Organic bases Nucleus Chromosome DNA Cell
œ Figure 3.2 (Top left) Linked molecules (organic bases) make up the "rungs" on DNA's twisted "molecular ladder." The order of these molecules serves as a code for genetic information.The code provides a genetic blueprint that is unique for each individual (except identical twins).The drawing shows only a small section of a DNA strand. An entire strand of DNA is composed of billions of smaller molecules. (Bottom left) The nucleus of each cell in the body contains chromosomes made up of tightly wound coils of DNA. (Don't be misled by the drawing: Chromosomes are microscopic in size, and the chemical molecules that make up DNA are even smaller.)
Father's genes
Brown-eyed mother Brown-eyed father
Mother's genes Brown-eyed child Brown-eyed child Brown-eyed child Blue-eyed child
œ Figure 3.3 Gene patterns for children of brown-eyed parents, where each parent has one brown-eye gene and one blue-eye gene. Since the brown-eye gene is dominant, one child in four will be blue-eyed.Thus, there is a significant chance that two brown-eyed parents will have a blue-eyed child.
CHILD DEVELOPMENT 95
color, and susceptibility to some diseases. To a degree, genetic instructions affect body size and shape, height, intelligence, athletic potential, personality traits, sexual orientation, and a host of other details (Hamer & Copeland, 1998). Score 1 for those who favor heredity as the more important factor in development!
Temperament
How soon do hereditary differences appear? Some appear right away. For instance, newborn babies differ noticeably in temperament.
This is the physical core of personality. It includes sensitivity, irritability, distractibility, and typical mood (Braungart et al., 1992). About 40 percent of all newborns are easy children, who are relaxed and agreeable. Ten percent are
difficult children, who are moody, intense, and easily angered.
Slow-to-warm-up children (about 15 percent) are restrained,
Genes Specific areas on a strand of DNA that carry hereditary information.
Polygenic characteristics Personal traits or physical properties that are influenced by many genes working in combination.
Dominant gene A gene whose influence will be expressed each time the gene is present.
Recessive gene A gene whose influence will be expressed only when it is paired with a second recessive gene.
Human growth sequence The pattern of physical development from conception to death.
Temperament The physical core of personality, including emotional and perceptual sensitivity, energy levels, typical mood, and so forth.
Easy child A child who is temperamentally relaxed and agreeable.
Difficult child A child who is temperamentally moody, intense, and easily angered.
Slow-to-warm-up child A child who is temperamentally restrained and unexpressive.
TABLE
3.1 Human Growth Sequence
*Note: There is no exact beginning or ending point for various growth periods.The ages are approximate, and each period may be thought of as blending into the next. (Table courtesy of Tom Bond.)
PERIOD DURATION DESCRIPTIVE NAME
Prenatal period From conception to birth Germinal period First 2 weeks after conception Zygote Embryonic period 2–8 weeks after conception Embryo Fetal period From 8 weeks after conception to birth Fetus
Neonatal period From birth to a few weeks after birth Neonate
Infancy From a few weeks after birth until child is walking securely; some children walk securely at less Infant than a year, while others may not be able to until age 17–18 months
Early childhood From about 15–18 months until about 2–21/2 years Toddler From age 2–3 to about age 6 Preschool child
Middle childhood From about age 6 to age 12 School-age child
Pubescence Period of about 2 years before puberty
Puberty Point of development at which biological changes of pubescence reach a climax marked by sexual maturity
Adolescence From the beginning of pubescence until full social maturity is reached (difficult to fix duration of Adolescent this period)
Adulthood From adolescence to death; sometimes subdivided into other periods as shown at left Adult Young adulthood (19–25) Adulthood (26–40) Maturity (41 plus)
Senescence No defined limit that would apply to all people; extremely variable; characterized by marked Adult (senile),“old age” physiological and psychological deterioration
© Myrleen F. Cate/PhotoEdit
Identical twins.Twins who share identical genes (identical twins) demonstrate the powerful influence of heredity. Even when they are reared apart, identical twins are strikingly alike in motor skills, physical development, and appearance.At the same time, twins are less alike as adults than they were as children, which shows environmental influences are at work (McCartney, Bernieri, & Harris, 1990).
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unexpressive, or shy. The remaining children do not fit neatly into a single category (Chess & Thomas, 1986). (Perhaps we should call them “generic” children?)
Imagine that we start with some infants who are very shy and some who are very bold. By the time they are 4 to 5 years old, most of these children will be only moderately shy or bold.
This suggests that inherited temperaments are modified by learning (Kagan, 1999). In other words, nurture immediately enters the picture.
Environment
Environment (“nurture”) refers to the sum of all external conditions that affect a person. The environments in which a child grows up can have a powerful impact on development. Humans today are genetically very similar to cave dwellers who lived 30,000 years ago. Nevertheless, a bright baby born today could learn to become almost anything—a ballet dancer, an engineer, a gangsta rapper, or a biochemist who likes to paint in watercolors. But an Upper Paleolithic baby could have only become a hunter or food gatherer. Score 1 for the environmentalists!
Early experiences can have very lasting effects.
For example, children who are abused may suffer lifelong emotional problems (Rutter, 1995). At the same time, extra care can sometimes reverse the effects of a poor start in life (Bornstein, 1995). In short, environmental forces guide human development, for better or worse, throughout life.
Sensitive Periods
Why do some experiences have more lasting effects than others? Part of the answer lies in sensitive periods. These are times when children are more susceptible to particular types of environmental influences.
Events that occur during a sensitive period can permanently alter the course of development (Bornstein, 1989). For instance, if a woman has German measles during early pregnancy, her child may be born with heart defects, cataracts, or hearing loss. Later in pregnancy, the child would escape without damage.
Often, certain events must occur during a sensitive period for a person to develop normally. For example, forming a loving bond with a caregiver early in life seems to be crucial for optimal development. Likewise, babies who don’t hear normal speech during their first year may have impaired language abilities (Thompson & Nelson, 2001).
Prenatal Influences
The impact of nurture actually starts before birth. Although the intrauterine environment (interior of the womb) is highly protected, environmental conditions can affect the developing child. For example, when Olivia was pregnant, Amy’s fetal heart rate and movements increased when loud sounds or vibrations penetrated the womb (Kisilevsky & Low, 1998).
If Olivia’s health or nutrition had been poor, or if she contracted German measles, syphilis, or HIV; used drugs; or was exposed to X-rays or atomic radiation, Amy might have been harmed. In such cases babies can suffer from
congenital problems, or “birth defects.” These problems affect the developing fetus and become apparent at birth. In contrast, genetic disorders are inherited from parents. Examples are sickle cell anemia, hemophilia, cystic fibrosis, muscular dystrophy, albinism, and some types of mental retardation.
Fetal Vulnerability
How is it possible for the embryo or the fetus to be harmed? No direct intermixing of blood takes place between a mother and her unborn child.Yet some substances—especially drugs—do reach the fetus. If a mother is addicted to morphine, heroin, or methadone, her baby may be born with an addiction. Most common prescription drugs also reach the fetus. Damage can be done by general anesthetics; cortisone; tetracycline; excessive amounts of vitamins A, D, B6, and K; some barbiturates, opiates, tranquilizers, steroids, and synthetic sex hormones (Rosenblith, 1992). Even aspirin, a seemingly safe drug, has been linked with lowered infant IQs when taken during pregnancy (Streissguth et al., 1987).
Repeated heavy drinking during pregnancy causes fetal alcohol syndrome (FAS). Affected infants have low birth weight, a small head, bodily defects, and facial malformations.Many also suffer from emotional, behavioral, and mental handicaps. Just one evening of binge drinking can permanently damage the brain of a developing fetus. To be completely safe, pregnant
Child abuse is a serious problem, but steps can be taken to prevent it.
See Chapter 4, pages 145–147, for more information.
B R I D G E S
© Photo Researchers
Because of the rapid growth of basic structures, the developing fetus is sensitive to a variety of diseases, drugs, and sources of radiation.This is especially true during the first trimester (3 months) of gestation (pregnancy).
CHILD DEVELOPMENT 97
women should avoid drinking alcohol (Mattson et al., 1998; Steinhausen & Spohr, 1998).
Tobacco is also harmful. Pregnant women who smoke greatly reduce the oxygen supply to the fetus. Heavy smokers risk miscarrying or having premature, underweight babies who are more likely to die soon after birth (Slotkin, 1998). Children of smoking mothers score lower on tests of language and mental ability (Fried et al., 1992). In other words, an unborn child’s future can easily “go up in smoke.”
Teratogens
Anything capable of causing birth defects is called a teratogen
(teh-RAT-uh-jen). Sometimes women are exposed to powerful teratogens, such as radiation, lead, pesticides, or PCBs, without knowing it (Eliot, 1999). But pregnant women do have direct control over many teratogens. For example, a woman who takes cocaine runs a serious risk of injuring her fetus (Arendt et al., 1998; Espy, Kaufmann, & Glisky, 1999; Singer et al., 1999; Swanson et al., 1999). In short, when a pregnant woman takes drugs, her unborn child does too.
Healthy Pregnancies/Healthy Babies
What can parents do to minimize prenatal risks? Several basic practices help promote successful pregnancies and healthy babies (Bradley, 1995). These include:
¡ Maintaining good nutrition during pregnancy
¡ Learning relaxation and stress reduction techniques to ease the transition to motherhood
¡ Avoiding teratogens and other harmful substances
¡ Getting adequate exercise during pregnancy
¡ Obtaining general education about pregnancy and childbirth
Childbirth
Does the way a child is born make a difference in later development?
Yes. In a traditional medicated birth the mother is given analgesics (painkillers) or general anesthetics, which cause a loss of consciousness. General anesthetics usually block a mother’s awareness of giving birth, and some infants are born partially anesthetized. In addition, drugs can reduce oxygen flow to the fetus. For such reasons, babies tend to lag in muscular and neural development if their mothers were heavily anesthetized.
Although medicated births are declining, 95 percent of all deliveries in the United States and Canada use some painkillers.
Certainly, a mother should not feel guilty if she needs pain relief.
Drugs injected near the spinal cord (an epidural block) can
Environment (“nurture”) The sum of all external conditions affecting development, including especially the effects of learning.
Sensitive period During development, a period of increased sensitivity to environmental influences. Also, a time during which certain events must take place for normal development to occur.
Congenital problems Problems or defects that originate during prenatal development in the womb.
Genetic disorders Problems caused by defects in the genes or by inherited characteristics.
Teratogen Radiation, a drug, or other substance capable of altering fetal development in ways that cause birth defects.
Medicated birth The common practice in Western medicine of giving painkilling drugs during labor and birth.
© Ted Wood
Some of the typical features of children suffering from fetal alcohol syndrome (FAS) include a small nonsymmetrical head, a short nose, a flattened area between the eyes, oddly shaped eyes, and a thin upper lip.Many of these features become less noticeable by adolescence.However,mental retardation and other problems commonly follow the FAS child into adulthood.The child shown here represents a moderate example of FAS.
© A. Glauberman/Photo Researchers
Changing attitudes toward childbirth have encouraged mothers and fathers to actively prepare for birth and to participate more fully in caring for the newborn.
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