Behavior Genetics: Predicting Individual Differences
We differ in personality, interests, physical appearance, family background, culture and native language. But we share a lot of similarities like our biological heritage and needs, our shared brain architecture, our ability to use language, the senses with which we explore the world around us and our social behavior. A fundamental question in psychology deals with the extent to which we are shaped by our heredity called our nature, and by our life history, called out nurture.
Behavior genetics are specially interested in the extend to which genetics and environment influences out behavior, creating individual differences. For this context, environment means everything external. Nongenetics aspect of our lives, from prenatal nutrition to the people and things around us now all belong to environment.
We have 46 chromosomes in each of our cells – 23 from our mother and 23 from our father. Chromosomes are threadlike structures made of DNA (deoxyribonucleic acid), a spiraling complex molecule containing genes, our approximately 30000 genes are DNA segments that, when “turned on” (expressed) form templates for the creation of various protein molecules, the building blocks of our physical and behavioral development. A genome is an organism's genetic profile-the complete set of instructions for making that organism, consisting of all genetic material in its chromosomes. Combinations of variations at particular gene sited help define our differences. Most human traits are influenced by many genes acting together, not by the influence of a single gene acting alone.
Identical Twins develop from one egg that slips after being fertilized. Hey share the same set of genes, a similar prenatal environment, and-usually-the same family and culture after birth. Fraternal Twins develop from separate fertilized eggs and share a prenatal environment, family, and social-cultural environment after birth, so they are genetically no more similar than any other two siblings. When some trait (such as extroversion) is present in both members of identical twin pairs but in only one member of fraternal twin pairs, researchers have a clue that heredity may be important in the development f that trait, Such comparisons are especially rich sources of information when twins have been separated at (or shortly after) birth, letting researchers see more clearly the effects of heredity on different environments.
Adopted children tend to resemble their biological parents in their personality (their characteristic pattern if thinking, feeling, and acting), and their adoptive parents in their values, attitudes, manners, faith, and politics.
Temperament is apparent soon after birth and tends to continue relatively unchanged into adulthood. This suggests that heredity plays a much larder roe than environment in the development of temperament.
Habitability describes the extent to which variation among individuals cam be attributed to genes. It applies only to differences among individuals – never to any one person. In an imaginary experiment that could create identical environments, any observed differences (in, for example, wight) among people would be 100 percent for that trait. Heritable individual differences in traits such as height or intelligence need to explain group differences. Genes mostly explain why some are taller than others, but not why people today are taller than a century ago, Saying that gene are self-regulating means that genes are not blueprints; they can react differently in different environments.
Some human traits develop in any environment, but man important psychological traits are a product of the interaction of our predispositions and our surrounding environment.
Evolutionary Psychology : Understanding Human Nature
Evolutionary psychologists attempt to understand how natural selection has shaped behaviors found throughout the human species.
The principle of natural selection states that,among the range of possible variations in a inherited trait, the variations most likely to be passed on to future generations are those that increase the odds of reproducing and surviving. Genes that enable a capacity to learn and to adapt had survival value for our ancestors , as did those that prepared people to survive in feast-or-famine conditions. We suffer the effects of famine less often, thanks to modern technology, but with a genetic legacy hat causes us to store fat and a decrease in rigorous exercise, we become obese. Charles Darwin, whose theory of evolution has for a long time been an organizing principle in biology, anticipated the contemporary applications of evolutionary principles in psychology.
Gender refers to the biologically and socially characteristics by which we define male and female. Men and women differ in their attitude towards sex: Men are more approving of casual sex, think about sex more often, and are more likely to misinterpret friendliness as sexual interest. Women are more likely to cite affection as a reason for this intercourse and to have a relational view of sexual activity. Similar differences appear in sexual behavior. Men masturbate more often, initiate sexual activity more frequently, and make more sacrifices to gain sex.
Applying principles of natural selection, evolutionary psychologists interpret human sexual behavior in term of its survival value – the tendency for behaviors to be selected if they increase the likelihood of sending one's genes into the future. Thus, being attracted to multiple healthy, fertile-appearing partners increase men's chances of spreading their genes widely and reproducing. Because women incubate and nurse babies, they increase their own and their children's chances of survival by searching for mates with economic recourses and social status, who have the potential for longterm mating and investment in their joint offspring.
One criticism of evolutionary explanations of human behaviors is that evolutionary psychologists start with an effect and work backward to an explanation. Another is that the evolutionary perspective underestimates cultural expectations and socialization. A third is that the evolutionary viewpoint absolves people from taking ethical and moral responsibility for their sexual behavior. Evolutionary psychologists respond that understanding out predispositions can help us overcome them. They also cite the value of testable predictions based in evolutionary principles, as well as the coherence and explanatory power of those principles.
Parents and Peers
Prenatal environments differ in terms of nutritions and exposure to toxic agents. Even identical twins sharing a placenta can, because of their differing locations, have unequal access to nourishment and protection from viruses.
During maturation, a child's neural connections increase in ares associated with repetitive activities (vision, for example). Unused synapses degenerate, as happen in the brain cells normally assign ti vision in the cortex of children, growth and pruning of synapses continue throughout life.
Freudian psychiatry and extreme environmentalism in early psychology contributed ti the idea that parents shape their children's futures. Parents do influence some areas of their children's lives, such as their manners and political and religious view. But in other areas, such as personality, the environment siblings share at home accounts for less than 10 percent of their differences.
Children, like adults, attempt to fit into groups by conforming, But children also seek out others who share their attitudes and interests; this selection contributes to peer group uniformity. Parents and peers are complementary influences in children's lives. Parents are important models for education, disciplines, responsibility, orderliness, charitableness, and ways of interacting with authorities. Peers are influential in such areas as learning to cooperate styles if interaction with people of a similar age. By choosing the neighborhood in which their children live, parents can exert some influence over the peer group culture that helps shape children.
Cultural influences
Culture is a set of enduring behaviors, ides, attitudes, values, and traditions shared by a group and transmitted from one generation to the next. Culture and out capacity fir language let us preserve innovations and pass them on to the next generation, as process that encourages diversity between groups. Despite cultural differences, out shared capacity for culture is a common thread running throughout the human species.
Cultures vary iin their ideas, attitudes, values and traditions. Those variations are embedded in each culture's norms, its rules for accepted and expected behavior. Newcomers or visitors to a culture different from their own may experience culture chock – confusion or frustration cause by their lack of understanding of the norms for observing personal space, expressing personal feelings, maintaining a faster or slower pace of life, or education and caring for children.
Cultures change rapidly. They change in their values, attitudes, and behaviors.
Cultures based on self-reliant individuals, like those of most of the united states, Canada, and Western Europe, value personal independence and individual achievement. Relationships tend to be more temporary and casual, confrontation is acceptable, and morality is self-defined. Individualist cultures tend to define identity in terms of self-esteem, personal goals and attributes, and personal right and liberties. Cultures based on socially connected collectivism, like those of many parts of Asia and Africa, value interdependence, tradition, and harmony. Relationships tend to be few, close, and enduring, and morality is based in duty to one's social network Collectivist cultures tend to define identity in terms of group goals and commitments and belonging to one's group.
Individualist cultures expect their members to be Independent and to think for themselves, and child-rearing practices in those cultures reflect these values Collectivist cultures, which emphasize a stronger sense of family self, tend to focus more on developing a sense of emotional closeness.
Although we human differ in our cultures, we share the same genetic profile, life cycle, capacity for language, biological needs, and need to belong. To the extent that biology and social forces predict behavior in individuals in one group, they often predict similar behaviors in those in other groups.
Gender Development
The major way human males and females are similar is in their genetic makeup, where 45 of 46 chromosomes are unisex. Males and females differ biologically in body fat, muscles, height, age of onset of puberty, and life expectancy. They also differ psychologically, for example, in their vulnerability to certain disorders: More women are diagnosed with depression, more men with antisocial personalty disorder.
Men more than women behave aggressively and describe themselves as aggressive. The aggression gender gap appears in many cultures and at various ages, especially for physical aggression.
In most societies, men are socially dominant and are perceived as such. Men tend to occupy more leadership positions, and their leadership style is more directive than women's.
Women, more than man, are concerned with making connections with others. This difference is noticeable is young children's play, and it continues throughout the teen years ad into adulthood. Women tend and befriend – they emphasize caring, often being responsible for the very young and very old. Bonds between women seem stronger and more supportive than those between men. Men tend to emphasize freedom and self-reliance.
Biological sex is determined by the twenty-third pair of chromosomes. In this pair, the mother's contribution is always an X chromosome. The father's contribution – which determines whether a child will be male or female - can be either an X or a Y. An XX combination produces a female; an XY combination produces a male. The Y chromosome contains a master switch for the production of the hormone testosterone, which triggers for the growth of external male sex organs in the seventh week of prenatal development. The fourth and fifth prenatal months are a second key period for sexual differentiation, influenced by a male fetus' greater testosterone or a female fetus' ovarian hormones. Gender is defined as the set of biologically and socially influenced characteristics by which people define male and female. Sex-related genes and hormones do influence gender differences in behavior, possibly by influencing brain development, but many gender differences are learned.
Our biology influences our gender, but cultures shape gender roles – expectations about how men and women should behave. Gender roles can vary form one place to another, and form one time to another within the same culture. A person's sense of being male or female is called gender identity, and some people more than other exhibit gender-typed (traditionally masculine or feminine) behavior. Social learning theory proposes that we learn cultural “recipe” of how to be male or female, which influences our behaviors and perceptions of what is appropriate for “people like us”.
Developing Through the Life Span
Prenatal Development and the Newborn
Developmental psychologists study physical, mental, and social changes throughout the life span. The three major issues are the relative influence of nature (heredity) and nurture (experience); whether development is a continuous process or a series of discrete stages; and whether personality is stable or changes as we age.
At conception, only one of the man's sperm can penetrate the outer coating of the women's egg before the egg's surface blocks out all the others. Within about 12 hours, the nuclei of the sperm and egg fuse into a single cell.
A zygote is a fertilized egg, whose cells become increasingly diverse. After about 10 days, the outer part of the cell mass attaches to mother's uterine wall and the inner cells soon become the embryo, beginning a stage of development when major organs form and begin to function. From 9 weeks after fertilization until birth, the organism, now known as a fetus, continues to develop and grow. Teratogens are potentially harmful agents that can pass through the placental screen and harm the developing embryo or fetus.
Infants are born with a number of automatic responses (reflexes) that aid survival, including, the rooting reflex that help them locate food. Newborns' rapidly developing senses of sight and hearing seem tuned to social events, such as a caretaker's face or voice. Researchers can discover some of what preverbal infants sense and think by observing how they react to novel stimuli )such as colors, shapes, and forms) and grow bored with (habituate to) familiar stimuli. To recognize a new stimulus, which indicates a simple form of learning.
Infancy and Childhood
A newborn's immature nervous system undergoes a rapid spurt after birth, as neural networks proliferate. Between ages 3 and 6, growth is most pronounced in the frontal lobes. Development in the association areas of the cortex enables thinking, memory , and language. Brain pathways continue to develop and strengthens with use until puberty, when pruning begins to eliminate excess connections. In the absence of severe abuse or neglect, maturation – the orderly sequence of genetically determined biological processes – guides all infants along the same general course of development.
Though the timing may vary, almost all babies follow the same sequence of first rolling over, then siting unsupported, then crawling, then walking. Experience has little influence; maturation, including that of the cerebellum, enables these events.
“Infantile amnesia” - an inability to consciously recall events that happened before age 3 – results form a change in the way the brain organizes memories at about that age. As the cortex matures, long-term storage increases; in addition, young children's preverbal memories are not easily transformed into language.
Piaget proposed that children's reasoning develops in a series of stages, and that children actively construct and modify their understanding of the world as they interact with it. They form schemas (concepts or frameworks for organizing experience). They then assimilate (interpret) information by means of these schemas – they accommodate (adjust) the schemas to incorporate the new information.
In the sensorimotor stage (birth to age 2), children experience the world through their senses and actions. In the first six months, infants lack object permanence, or the awareness that things exist when out of sight. In the preoperational stage (age 2 to about 6 or 7), children learn to use language and can represent things with words and images, but they are unable to reason logically. They lack a theory of mind an are egocentric, or have difficulty taking another person's point of view (people with the disorder autism also lack a theory of mind). Preoperational children have no concept of conversation – the understanding that things can change form but retain their mass, volume, or number. In the concrete operational stage (about age 7 to 11), children can think logically about concrete events, grasp analogies, and perform arithmetical operations. In the formal operational stage (12 through adulthood), they gain the ability to reason abstractly. Piaget viewed the ages connected with these stages as approximate, but the sequence as universal.
Contemporary research shows that formal logic plays a smaller part in cognitive development than Piaget believed, and that the development of cognitive abilities is more continuous, with stages starting earlier and less abruptly. Nevertheless, Piaget's views about the sequence of development of children's cognitive abilities have been supported repeatedly.
Stranger anxiety is the fear of stranger that infants begin to display at about 8 months of age. Children of this age have formed schemas for familiar faces, and they become distressed when faces do not match their schemas.
Until the Harlows' research in the mid – 1950s, many psychologists believed that, through a conditioning process, children become attached (form an emotional tie) to those who provide nourishment. The Harlows' experiments showed that infant monkeys would search out a non-nourishing “mother” that provided comfort in presence to one that provided nourishment without comfort. Ducks and other animals imprint, forming an attachment to a significant organism or object during a critical period (a time shortly after birth when proper development depends on exposure to certain stimuli or experiences). Humans do not imprint, but they do become attached to familiar people and things, which provide feelings of safety.
In the experimental condition called the strange situation, researchers observe a mother and her child in a laboratory playroom, taking note of the child's reactions as the mother leaves and reenters. Securely attached children play and explore comfortably in the mother's presence and may cling to her, cry loudly when she leaves, and remain upset or act indifferent when she returns. Other studies show that sensitive parenting, but parental tend to have securely attached children. Genetically influenced temperament may evoke responsive parenting, but parental sensitivity has been taught and does increase infant attachment security to some extent. Father love as well as mother love is a predictor of children's health and well-being. Adult relationships tend to reflect the secure or insecure attachment styles of early childhood, lending support to Erik Erikson's idea that basic trust in infancy by our experiences with responsive caregivers.
When parental neglect or other trauma deprive children of the opportunity to form attachments, children become withdrawn and frightened and may not develop speech. If prolonged, childhood abuse children are at risk for a variety of physical, psychological, and social problems and may alter the brain's production of serotonin. Damage from disruption of attachment bonds, as happens when children are placed in foster care, appears to be minimal before 16 months of age. Children who are moved repeatedly or otherwise prevented from forming attachments by age 2, however, may be at risk for attachment problems. Quality day care, with responsive adults interaction with children on a safe and stimulating environment, does not appear to harm children's thinking and language skills, but some studies have linked extensive time in day care with increased aggressiveness and defiance.
Self-concept, a sense of one's identity and personal worth emerges gradually, beginning at about 6 months. At 15 to 18 months, children recognize themselves in a mirror. By school age, they can describe many of their own traits' and by age 8 to 10, their self-image is stable.
Authoritarian parents impose rules and expect obedience. Permissive parents submit to children's demands, ask little, and punish rarely. Authoritative parents are demanding but responsive to their children. Authoritative parenting correlates with social competence, but the cause-effect relationship is not clear. This style of parenting may produce socially competent children, or agreeable easygoing children may evoke authoritative parenting style and that manifests itself in agreeable easygoing social interactions.
Adolescence
Adolescence is t he transition period from childhood to adulthood, extending from puberty to independence.
Adolescence begins with puberty, the period of sexual maturation that enables reproduction. A surge of hormones triggers a two-year growth spurt, beginning at about age 11 in girls and age 13 in boys. Primary sex characteristics (the reproductive organs and external genitalia) and secondary sex characteristics (nonreproductive sexual characteristics such as a girl's breasts and a boy's deepened voice) develop during puberty, though the exact timing varies from one person to another. For most girls, menarche happens within a year of age 12. For most boys, spermarche occurs by about age 14. Heredity and environment interact and other people's reactions to early or late maturations can influence adolescents' adjustments. There is also significant brain development during adolescence, with frontal lobe maturation and selective pruning of unused neurons and their connections.
With the development of formal operations, adolescents gain the ability to reason abstractly. This ability lets them form hypotheses and deduce consequences.
In Piaget's view, moral judgments reflect the developing child's reasoning powers. Lawrence Kohlberg proposed three levels of moral thinking. Preconventional morality is self-interested morality based in reasoning that attempts to avoid punishment or gain concrete rewards. Conventional morality is law-aiding morality based in reasoning that existing laws must be upheld. Postconventional morality based in abstract reasoning about what is ethical, right, and fair. The social intuitionist view if morality proposes that moral feeling precede moral thinking and judgments. Some brain-imaging experiments confirm that the brain's emotion areas are active when people consider moral dilemmas. The moral action perspective focuses in social influences on decision to do the right thing. Programs based on the moral action perspective teach children to empathize with others' feelings and to delay gratification to enable bigger rewards later.
Erik Erikson proposed that we pass through eight stages in life (loosely associated with age), each with its worn psychosocial task. In infancy (to 1 year), the issue is trust versus mistrust, in toddlerhood (1 to 2 years), the issue is autonomy versus shame and doubt. Preschoolers (2 to 5) learn initiate or guilt, and elementary school children (6 to puberty), competence or inferiority. A chief task of adolescence (teens to young adults).
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