Developmental Psychology Developmental psychology is the study of how behaviors and thoughts change throughout a person’s lifespan. This is one of the most comprehensive topics in psychology, and it covers numerous concepts.

Human Development All psychologists acknowledge the importance of both nature and nurture as they apply to the psychological development of an individual. By studying identical twins who grew up in completely different environments, researchers are better able to understand how differently nature (genetic factors) and nurture (environmental factors) influence development. The famous Bouchard Twin Study has shown that identical twins who were reared in different homes had an equal chance of having similar personalities, interests, and attitudes as twins who were raised together. Such studies support the idea that nature plays a profound role in development. Some psychologists argue that people develop psychologically at a steady rate from birth to death. This theory is referred to as continuity. However, other psychologists believe that development occurs in stages, some of which are more rapid than others. This theory is referred to as discontinuity. Those who argue for the latter, including Erik Erikson and Sigmund Freud, have attempted to explain the stages in which people develop. Another argument relating to human development concerns stability versus change. Psychologists study and develop theories relating to whether people's behaviors or core personality traits stay the same or whether they change over time.

Prenatal Influences on Development The first critical period of development begins in the womb, after fertilization. From the time an egg is fertilized to the time of birth, there is tremendous growth—a single cell develops into an organism with behavioral capabilities, all occurring in a nine-month period. Certain environmental exposures, however, such as cigarette smoke, substance abuse, nutrition, and illnesses, can harm the health and progress of the baby. Many developmental psychologists study the ways in which genetics influence human development. Most prenatal influences are primarily genetic in origin, but the environment can also play a role in development. For example, the placenta can filter out numerous substances that are harmful to an unborn fetus; however, there are some chemicals (teratogens) that can pass through the placenta and affect the baby in a negative way. The most common teratogen is alcohol, and unfortunately, not all expectant mothers abstain from drinking while pregnant. Fetal alcohol syndrome is often the result.

Motor and Sensory Development Many developmental psychologists believe that motor and sensory development occur through maturation, which is defined as an inevitable progression of behavior patterns that

are genetically programmed. Although certain babies may progress at a higher rate than others, the steps babies take in their behavioral schedule are essentially the same. All babies crawl before they walk. Maturation theorists believe that motor and sensory development occur independently of environmental conditions.

Parenting and Development Attachment, the reciprocal relationship between a caregiver and a child, is an important aspect of human development. Mary Ainsworth (1913-1999) studied different types of attachments between infants and their caregivers. In one particular study, children were placed in an unfamiliar setting with their mothers and unknown women. When the mothers were present, many of the children played happily and explored their surrounding environment. After the mothers returned from a brief absence, the children displayed feelings of happiness. This infant reaction was the most common, with roughly 66 percent of the participants demonstrating secure attachments. About 21 percent of the infants displayed avoidant attachments by resisting comfort from parents and exploring their new environment. Twelve percent of the infants had anxious/ambivalent attachments, and they displayed extreme distress at being left by their parents but resisted being comforted when the parents returned.

Stage Theories of Development Sigmund Freud theorized that children develop through four psychosexual stages:    

oral stage: Infants seek pleasure through their mouths. anal stage: Development occurs through toilet training. phallic stage: Babies realize their gender and either develop the Oedipus complex (males) or the Electra complex (females). genital stage: Focus of pleasure shifts to the genitals.

Erik Erikson, a neo-Freudian, developed his eight stages of social development to correspond roughly with Freud's psychosexual stages:

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trust versus mistrust: The first social experience of children is based solely on the needs of fulfillment; sense of trust or mistrust will carry throughout the rest of an individual's life, according to Erikson. autonomy versus shame and doubt: Toddlers begin to exert their own will over their bodies and their environment in this stage. initiative versus guilt: Children take the initiative in problem-solving and attempt to understand the world; this initiative can be repressed if a child is made to feel ashamed for asking questions. industry versus inferiority: Children begin their formal education and are asked to produce work that is evaluated; low-performing children may develop an inferiority complex about their performance.

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identity versus role confusion: Adolescents attempt to discover what social identity they are most comfortable with and may "try on" several different roles before finding one that best fits his or her internal sense of self. intimacy versus isolation: Young adults who have established stable identities attempt to figure out how to balance their efforts between work (including school and self-improvement) and relationships with others. generativity versus stagnation: Adults begin looking critically at their lives and attempt to determine what kind of life they want for themselves and their families. integrity versus despair: Toward the end of life, adults look back at their accomplishments and decide if they are satisfied with them or not.

Cognitive Development Developmental psychologists study the ways in which children understand and evaluate the world. One of the most famous theories of this type was developed by Swiss psychologist Jean Piaget (1896-1980). Piaget's four-stage theory of cognitive development consists of the following stages: The sensorimotor stage begins at birth and lasts until approximately two years of age. Babies begin to explore the world through their senses, and their behavior is governed by their innate reflexes. During this stage, babies attempt to develop object permanence, which is the realization that objects exist even when they cannot see them. The preoperational stage is experienced by children from approximately two to seven years of age. During this stage, children start to use symbols to represent real-world objects, which is the beginning of language. Piaget argued that children are egocentric in this stage and cannot grasp the idea that there are any points of view other than their own. According to Piaget, children between the approximate ages of eight and 12 are in the concrete operational stage of cognitive development. During this stage, children demonstrate knowledge of concepts of conservation, meaning they can mathematically and logically classify objects. The formal operations stage, which begins around the age of 11 or 12, brings cognition into its final form. People begin to think about abstract concepts. Logical thought and deductive reasoning also emerge during this period. Children continue to develop through this stage into adulthood. Piaget's theory is not universally accepted by psychologists, although his insights into child development have proven very valuable. The information processing model, an alternative theory to Piaget's, suggests that cognitive skills develop gradually rather than in distinct stages.

Moral Development American psychologist Lawrence Kohlberg (1927-1987) developed a stage theory to describe how humans develop morality and think about ethical situations. He gathered his

data by asking a subject group of children and adolescents to respond to hypothetical moral situations. For example, Kohlberg presented the Heinz dilemma, in which a man is unable to afford medication for his dying wife and considers stealing it from the store, and categorized the participants' responses according to three levels of moral development. The pre-conventional stage of Kohlberg's theory involves the avoidance of punishment. For instance, when faced with a moral dilemma, one is most likely to make his or her choice based on the possibility of punishment. This is the earliest stage of moral development and is especially common in young children whose moral reasoning is limited to how the choice affects them personally. In regard to the Heinz dilemma, children at this stage might say that the possible consequences of the theft (arrest or imprisonment) would outweigh the benefits of saving a life. In the conventional stage, children are able to move past personal gain or loss and evaluate a moral choice from another person's perspective. Children learn conventional standards of morality from those around them and are affected by how others will perceive their moral choices. Thus, they may react to the Heinz dilemma by saying that Heinz should save his wife because others will consider him heroic. Those individuals who progress to the post-conventional stage of moral development would likely approach the Heinz dilemma by reasoning that theft of the drug is acceptable because Heinz has the right to protect his wife's life. The post-conventional stage includes the conception that society should work toward the benefit of all. People at this level of moral reasoning would want to protect the individual rights that are promised within society, which would definitely include the life of Heinz's wife. Although people within this stage did not generally favor breaking the law, the fact that a person's life was in danger overrode every other standard that may be used to judge Heinz's actions. Kohlberg's theories are not universally accepted by developmental psychologists. Carol Gilligan and other researchers introduced criticisms of Kohlberg's work relating to gender differences. Gilligan disagreed with Kohlberg's assumption that males and females come to moral conclusions in the same way. Gilligan studied the different ways in which males and females develop their morals and ethics. She discovered that males have a more absolute view of morality, while females give more weight to the situational factors. Kohlberg did not account for this difference while conducting his research, particularly the Heinz dilemma study.

Gender and Development Biologically speaking, it would seem uncomplicated to explain what makes a person develop a certain gender identity. Humans are, in most cases, either born with XX or XY chromosome pairs, making them male or female. However, psychologically speaking, it is not this simple. For example, gender identity may not coincide with biological traits. A person may be born female and feel an inner sense that relates strongly to being male. The same holds true for someone born male but who identifies more with being female. The evolutionary theory of gender development argues that males and females face fundamental differences through natural selection. For instance, females are nurturers, and

males need certain skills as protectors and providers. These differences date back to a time when humans formed hunter-gatherer societies. These characteristics suggest that gender development is innate. This theory is in sharp contrast to cognitive theorists who argue that our gender development is based on our observance of gender roles at a young age. Freud's psychoanalytic theory explains that a child's gender identity is determined through identification—the child models himself or herself after the same-sex parent.This is done in an effort to become more like him or her. This identification, according to Freud, occurs after the resolution of the Oedipal or Electra complex. Social learning theorists argue that gender development is based on imitation, generally of same-sex parents and significant role models. More importantly, this imitation is the result of positive reinforcement (rewards) and the desire to avoid negative reinforcement (punishment). For example, parents will reward a young girl for helping her mother in the kitchen or reward a young boy for helping his father with the yard work. Cognitive psychologists argue that gender roles are developed through the observation and internal interpretations of a person's environment. For instance, in certain cultures, a girl may see her brother playing a rough game of football in the backyard while her sister is hosting a tea party with her friends in the bedroom. Upon internalizing these messages, the girl will most likely create cognitive rules about how each gender should act and behave. This theory is known as gender schema, which was introduced by psychologist Sandra Bem and supported by the cognitive psychologists Jean Piaget and Lawrence Kohlberg.

Research Methodologies and Human Development Developmental psychologists usually conduct either cross-sectional or longitudinal studies. Cross-sectional research focuses on a certain variable in a specific point in time. This is unlike longitudinal research, which takes place over an extended period in time. Cross-sectional research examines various sample groups, such as participants of different age groups, and compares them to one another, whereas longitudinal research examines only one particular group. Longitudinal research involves a study or studies that take place over extended periods of time; the study may not be concluded for years or decades. A researcher who is following a group of children and their developmental progress over time is an example of a longitudinal study. This is not a quick test but a study that will likely follow a student from grade school to graduation. Longitudinal studies are able to precisely measure the effects of development on a specific group.