Chapter 3 Human Development. Heredity and Genes. Developmental Psychology: The study of progressive changes in behavior and abilities Heredity (Nature): Transmission of physical and psychological characteristics from parents to their children through genes
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.)
FIGURE 3.3 Gene patterns for children of brown-eyed parents, where each parent has one brown-eye gene and one blue-eye gene. Because the brown-eye gene is dominant, one child in four will be blue-eyed. Thus, there is a significant chance that two browneyed parents will have a blue-eyed child.
FIGURE 3.6 Motor development. Most infants follow an orderly pattern of motor development. Although the order in which children progress is similar, there are large individual differences in the ages at which each ability appears. The ages listed are averages for American children. It is not unusual for many of the skills to appear 1 or 2 months earlier than average or several months later (Frankenberg & Dodds, 1967; Harris & Liebert, 1991). Parents should not be alarmed if a child’s behavior differs some from the average.
FIGURE 3.8 The traditional view of infancy holds that emotions are rapidly differentiated from an initial capacity for excitement.
FIGURE 3.9 Infants display many of the same emotional expressions as adults do. Carroll Izard believes such expressions show that distinct emotions appear within the first months of life. Other theorists argue that specific emotions come into focus more gradually, as an infant’s nervous system matures. Either way, parents can expect to see a full range of basic emotions by the end of a baby’s first year.
FIGURE 3.10 In the United States, about two thirds of all children from middle-class families are securely attached. About one child in three is insecurely attached. (Percentages are approximate. From Kaplan, 1998.)
FIGURE 3.11 This graph shows the results of a study of child care in homes other than the child’s. In most cases, parents paid for this care, although many of the caregivers were unlicensed. As you can see, child care was “good” in only 9 percent of the homes. In 35 percent of the homes, it was rated as inadequate
FIGURE 3.12 Mother-infant and father-infant interactions. These graphs show what occurred on routine days in a sample of 72 American homes. The graph on the left records the total amount of contact parents had with their babies, including such actions as talking to, touching, hugging, or smiling at the infant. The graph on the right shows the amount of caregiving (diapering, washing, feeding, and so forth) done by each parent. Note that in both cases mother-infant interactions greatly exceed father-infant interactions.
FIGURE 3.13 Infant engagement scale. These samples from a 90-point scale show various levels of infant engagement, or attention. Babies participate in prelanguage “conversations” with parents by giving and withholding attention and by smiling, gazing, or vocalizing.
FIGURE 3.14 This graph shows the development of turn-taking in games played by an infant and his mother. For several months, Richard responded to games such as peek-a-boo and “hand-the-toy-back” only when his mother initiated action. At about 9 months, however, he rapidly began to initiate action in the games. Soon, he was the one to take the lead about half the time. Learning to take turns and to direct actions toward another person underlie basic language skills.
FIGURE 3.16 The panels on the left show a possible event, in which an infant watches as a toy is placed behind the right of two screens. After a delay of 70 seconds, the toy is brought into view from behind the right screen. In the two panels on the right, an impossible event occurs. The toy is placed behind the left screen and retrieved from behind the right. (A duplicate toy was hidden there before testing.) Eight-month-old infants react with surprise when they see the impossible event staged for them. Their reaction implies that they remember where the toy was hidden. Infants appear to have a capacity for memory and thinking that greatly exceeds what Piaget claimed is possible during the sensorimotor period.
FIGURE 3.17 Dramatic differences in physical size and maturity are found in adolescents of the same age. The girls pictured are all 13, the boys 16. Maturation that occurs earlier or later than average can affect the “search for identity.”