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changes in fat distribution, loss of hair pigmentation, and wrinkling of the skin are changes associated with advances in age. In females at about age 50, menopause—cessation of the ability to reproduce—is accompanied by a decrease in production of female sex hormones. Men experience a more gradual decline in reproductive function as they age. Typically, as adults age the lenses of their eyes thicken, letting less light reach the retina and worsening vision for near objects; ability to detect high-pitched sounds decreases; and sensitivity to tastes, odors, and temperature may decrease. Neural processes slow and parts of the brain begin to atrophy. Physical signs of aging can be slowed, and to some extent reversed, if we stay physically and mentally active and have a healthy diet. Heart disease, stroke, cancer, Alzheimer’s, and other degenerative diseases are often terminal diseases of old age. Since they do not interfere with reproductive success, genes involved in these diseases do not incur any selective pressures. On average, men die about 4 years earlier than women.

Theories of Cognitive Development

Theories of cognitive development look at how our patterns of thinking, reasoning, remembering, and problem solving change as we grow. Most developmental theories focus on infancy, childhood, and adolescence.

Jean Piaget’s Theory of Cognitive Development

Swiss psychologist Jean Piaget developed a stage theory of cognitive development based on decades of careful observation and testing of children. His theory has been very influential because Piaget recognized that children think differently from adults. He thought that certain cognitive structures were innate, but only through a child’s interaction with the environment could they grow and develop over time.

Piaget believed that all knowledge begins with building blocks called schemas, mental representations that organize and categorize information processed by our brain. Through the process of assimilation, we fit new information into our existing schemas. Through the process of accommodation we modify our schemas to fit new information. As babies, we learn through accommodation that not all people fit our schema of mommy.

Sensorimotor (First) Stage

Piaget called the first stage of cognitive development, from birth to approximately 2 years, the sensorimotor stage, during which the baby explores the world using his/her senses and motor interactions with objects in the environment. The concept of object permanence—that objects continue to exist even when out of sight—to Piaget seemed to develop suddenly between 8 and 10 months. Piaget said that the 5-month-old who sees a toy does not search for it if it disappears, but a 9-month-old does. Recently, psychologists have found that object permanence seems to develop gradually; young infants gaze where they saw a toy that disappeared. According to Piaget, infants at about 8 months of age also seem to develop stranger anxiety, fear of unfamiliar people, indicating that they can differentiate among people they know and people they don’t know.

Preoperational (Second) Stage

To Piaget, attainment of object permanence and stranger anxiety indicated that cognitive structures had matured sufficiently for the typical 2-year-old to represent and manipulate objects with symbols such as words, whether or not the objects were present, which characterizes Piaget’s second stage, the preoperational stage. From approximately 2 to 7 years, language develops with the ability to think. The child is mainly egocentric, seeing the world from his/her own point of view. Egocentrism is consistent with a belief called animism, that all things are living just like him/her; and the belief, called artificialism, that all objects are made by people. While preoperational, a child uses trial and error to figure out how things work and answers questions intuitively rather than logically. He/she sometimes demonstrates magical thinking, reasoning that something happens because he/she wishes it to happen.

Concrete Operational (Third) Stage

During Piaget