calorie restriction The practice of limiting dietary energy intake (while consuming sufficient quantities of vitamins, minerals, and other important nutrients) for the purpose of improving health and slowing down the aging process.

carrier A person whose genotype includes a gene that is not expressed in the phenotype. The carried gene occurs in half of the carrier’s gametes and thus is passed on to half of the carrier’s children. If such a gene is inherited from both parents, the characteristic appears in the phenotype.

case study An in-depth study of one person, usually requiring personal interviews to collect background information and various follow-up discussions, tests, questionnaires, and so on.

cellular aging The cumulative effect of stress and toxins, causing first cellular damage and eventually the death of cells.

centration A characteristic of preoperational thought in which a young child focuses (centers) on one idea, excluding all others.

cerebral palsy A disorder that results from damage to the brain’s motor centers. People with cerebral palsy have difficulty with muscle control, so their speech and/or body movements are impaired.

cesarean section (c-section) A surgical birth, in which incisions through the mother’s abdomen and uterus allow the fetus to be removed quickly, instead of being delivered through the vagina. (Also called simply section.)

charter school A public school with its own set of standards that is funded and licensed by the state or local district in which it is located.

child abuse Deliberate action that is harmful to a child’s physical, emotional, or sexual well-being.

child culture The particular habits, styles, and values that reflect the set of rules and rituals that characterize children as distinct from adult society.

child maltreatment Intentional harm to or avoidable endangerment of anyone under 18 years of age.

child neglect Failure to meet a child’s basic physical, educational, or emotional needs.

child sexual abuse Any erotic activity that arouses an adult and excites, shames, or confuses a child, whether or not the victim protests and whether or not genital contact is involved.

child-directed speech The high-pitched, simplified, and repetitive way adults speak to infants and children. (Also called baby talk or motherese.)

childhood obesity In a child, having a BMI above the 95th percentile, according to the U.S. Centers for Disease Control’s 1980 standards for children of a given age.

childhood overweight In a child, having a BMI above the 85th percentile, according to the U.S. Centers for Disease Control’s 1980 standards for children of a given age.

choice overload Having so many possibilities that a thoughtful choice becomes difficult. This is particularly apparent when social networking and other technology make many potential romantic partners available.

chromosome One of the 46 molecules of DNA (in 23 pairs) that virtually each cell of the human body contains and that, together, contain all the genes. Other species have more or fewer chromosomes.

chronic illness An illness that begins gradually and is ongoing.

circadian rhythm A day–night cycle of biological activity that occurs approximately every 24 hours (circadian means “about a day”).

classical conditioning The learning process in which a meaningful stimulus (such as the smell of food to a hungry animal) is connected with a neutral stimulus (such as the sound of a tone) that had no special meaning before conditioning. (Also called respondent conditioning.)

classification The logical principle that things can be organized into groups (or categories or classes) according to some characteristic they have in common.

clinical depression Feelings of hopelessness, lethargy, and worthlessness that last two weeks or more.

cluster suicides Several suicides committed by members of a group within a brief period of time.

cognitive artifacts Intellectual tools passed down from generation to generation which may assist in learning within societies.

cognitive equilibrium In cognitive theory, a state of mental balance in which people are not confused because they can use their existing thought processes to understand current experiences and ideas.

cognitive theory A grand theory of human development that focuses on changes in how people think over time. According to this theory, our thoughts shape our attitudes, beliefs, and behaviors.

cohabitation An arrangement in which a couple live together in a committed romantic relationship but are not formally married.

cohort A group defined by the shared age of its members, who, because they were born at about the same time, move through life together, experiencing the same historical events and cultural shifts.

comorbid Refers to the presence of two or more unrelated disease conditions at the same time in the same person.

complicated grief A type of grief that impedes a person’s future life, usually because the person clings to sorrow or is buffeted by contradictory emotions.

compression of morbidity A shortening of the time a person spends ill or infirm, accomplished by postponing illness.

compulsive hoarding The urge to accumulate and hold on to familiar objects and possessions, sometimes to the point of their becoming health and/or safety hazards. This impulse tends to increase with age.

concrete operational thought Piaget’s term for the ability to reason logically about direct experiences and perceptions.

conditioning According to behaviorism, the processes by which responses become linked to particular stimuli and learning takes place. The word conditioning is used to emphasize the importance of repeated practice, as when an athlete conditions his or her body to perform well by training for a long time.

consequential strangers People who are not in a person’s closest friendship circle but nonetheless have an impact.

conservation The principle that the amount of a substance remains the same (i.e., is conserved) even when its appearance changes.

control processes Mechanisms (including selective attention, metacognition, and emotional regulation) that combine memory, processing speed, and knowledge to regulate the analysis flow of information within the information-processing system. (Also called executive processes.)

conventional moral reasoning Kohlberg’s second level of moral reasoning, emphasizing social rules.

copy number variations Genes with various repeats or deletions of base pairs.

corporal punishment Punishment that physically hurts the body, such as slapping, spanking, etc.

corpus callosum A long, thick band of nerve fibers that connects the left and right hemispheres of the brain and allows communication between them.

correlation A number that indicates the degree of relationship between two variables, expressed in terms of the likelihood that one variable will (or will not) occur when the other variable does (or does not). A correlation indicates only that two variables are related, not that one variable causes the other to occur.

cortex The outer layers of the brain in humans and other mammals. Most thinking, feeling, and sensing involves the cortex.

cortisol The primary stress hormone; fluctuations in the body’s cortisol level affect human emotion.

co-sleeping A custom in which parents and their children (usually infants) sleep together in the same room.

couvade Symptoms of pregnancy and birth experienced by fathers.

creative intelligence A form of intelligence that involves the capacity to be intellectually flexible and innovative.

critical period A time when a particular type of developmental growth (in body or behavior) must happen if it is ever going to happen.

cross-sectional research A research design that compares groups of people who differ in age but are similar in other important characteristics.

cross-sequential research A hybrid research design in which researchers first study several groups of people of different ages (a cross-sectional approach) and then follow those groups over the years (a longitudinal approach). (Also called cohort-sequential research or time-sequential research.)

crystallized intelligence Those types of intellectual ability that reflect accumulated learning. Vocabulary and general information are examples. Some developmental psychologists think crystallized intelligence increases with age, while fluid intelligence declines.

culture A system of shared beliefs, norms, behaviors, and expectations that persist over time and prescribe social behavior and assumptions.

cyberbullying Bullying that occurs when one person spreads insults or rumors about another by means of emails, text messages, or cell phone videos.