Chapter 1 The Biological Approach To Psychology

The Biological Approach to Behavior (cont’d.) Biological psychology: the study of the physiological, evolutionary and developmental mechanisms of behavior and experience A strong emphasis is placed upon brain functioning

The Biological Approach to Behavior (cont’d.)

The Biological Approach to Behavior (cont’d.) Brain functioning can be explained at a more microscopic level in terms of neuron and glia activity Neurons and glia somehow produce an enormous wealth of behavior and experience

The Biological Approach to Behavior (cont’d.)

Biological Explanations of Behavior Physiological: relates a behavior to the activity of the brain and other organs Ontogenetic: describes the development of a structure or behavior including the influences of genes, nutrition, and experiences Evolutionary: reconstructs evolutionary history of a behavior or structure Functional: describes why a structure or behavior evolved as it did

Biological Explanations of Behavior (cont’d.)

Genetics and Behavior Both genes and environment interact to shape human behavior The fundamental issue is how much a role each factor plays in shaping human behaviors Examples: psychological disorders, weight gain, personality, sexual orientation Researchers examined facial expressions of people who were born blind and therefore could not have learned to imitate facial expressions

Mendelian Genetics Gregor Mendel demonstrated that inheritance occurs through genes Genes are aligned along chromosomes (strands of genes) and come in pairs

Mendelian Genetics (cont’d.) A gene is a portion of a chromosome and is composed of deoxyribonucleic acid (DNA) DNA serves as a model for the synthesis of ribonucleic acid (RNA)

Mendelian Genetics (cont’d.) RNA is a single strand chemical that can serve as a template/ model for the synthesis of proteins Proteins determine the development of the body by: Forming part of the structure of the body Serving as enzymes, biological catalysts that regulate chemical reactions in the body

Mendelian Genetics (cont’d.)

Mendelian Genetics (cont’d.) Homozygous, for, a gene means that a person has an identical pair of genes on the two chromosomes Heterozygous, for a gene, means that a person has an unmatched pair of genes on the two chromosomes

Mendelian Genetics (cont’d.) Genes are either dominant, recessive, or intermediate Examples: eye color, ability to taste PTC A dominant gene shows a strong effect in either the homozygous or heterozygous condition A recessive gene shows its effect only in the homozygous condition

Mendelian Genetics (cont’d.) Examples such as PTC and hair color can be misleading Implies that a single gene combination completely controls a characteristic, but this is not true Some genes are only expressed partly: in some cells and not others or only under certain circumstances

Mendelian Genetics (cont’d.) Types of genes include: Autosomal genes: all other genes except for sex- linked genes Sex-linked genes: genes located on the sex chromosomes In mammals, the sex chromosomes are designated X & Y Females have two X chromosomes (XX) Males have an X and a Y chromosome (XY)

Mendelian Genetics (cont’d.) During reproduction: Females contribute an X chromosome Males contribute either an X or a Y chromosome that determines the sex of the child If an X chromosome is contributed by the male, the offspring is female If a Y chromosome is contributed by the male, the offspring will be male

Mendelian Genetics (cont’d.)

Mendelian Genetics (cont’d.) The human Y chromosome has genes for 27 proteins The human X chromosome has genes for approximately 1500 proteins Thus, sex-linked genes usually refer to X-linked genes: e.g., red-green color deficiency) Sex-limited genes are genes that are present in both sexes but mainly have an effect on one sex (chest hair, breast size, etc.)

Mendelian Genetics (cont’d.) Genes change in several ways: Mutation: a heritable change in a DNA molecule Microduplication/microdeletion: part of a chromosome that might appear once might appear twice or not at all Example: some researchers believe schizophrenia might be a result of microduplications and microdeletions of brain-relevant genes

Mendelian Genetics (cont’d.) Epigenetics: a field that is concerned with changes in gene expression without the modification of the DNA sequence Some genes are active only at a certain point in one’s life, a certain time of day, etc. Changes in gene expression are central to learning and memory Epigenetic differences are a likely explanation for differences between monozygotic “identical” twins

Mendelian Genetics (cont’d.)

Mendelian Genetics (cont’d.) What you do at any moment not only affects you now, but produces epigenetic effects that alter gene expressions for a longer period of time Experiences like maternal deprivation, cocaine exposure, new learning, alter the activity of genes Mice given some dietary supplements have epigenetic changes affecting expression of some genes, which affects their fur color, weight, and propensity to develop cancer

Heredity and Environment Almost all behaviors have both a genetic component and an environmental component Researchers study monozygotic (“from one egg”) and fraternal/dizygotic (“from two eggs”) twins to infer contributions of heredity and environment Researchers also study adopted children and their resemblance to their biological parents to infer hereditary influences

Heredity and Environment (cont’d.) Heritability refers to how much characteristics depend on genetic differences Researchers have found evidence for heritability in almost every behavior (e.g. speed of second language learning) tested Heritability of a certain trait is specific to a given population Strong environmental influences may cause genetic influences to have less of an effect

Heredity and Environment (cont’d.) Traits with a strong hereditary influence can by modified by environmental intervention e.g., PKU: a genetic inability to metabolize the amino acid phenylketonuria If PKU is not treated, phenylalanine accumulates to toxic levels, impairing brain development Environmental interventions (strict low-phenylalanine diet) can modify PKU

PKU

Heredity and Environment (cont’d.) Genes do not directly produce behaviors Genes produce proteins that increase the probability that a behavior will develop under certain circumstances Genes can also have an indirect affect Genes can alter your environment by producing behaviors or traits that alter how people in your environment react to you

Heredity and Environment (cont’d.) Suppose your genes make you unusually attractive. As a result, strangers smile at you and many people want to get to know you. Their reactions to your appearance may change your personality, and if so, the genes altered your behavior by altering your environment.

The Evolution of Behavior Evolution refers to a change in the frequency of various genes in a population over generations Regardless if helpful or harmful to the species Evolution attempts to answer two questions: How did some species evolve? How do species evolve?

The Evolution of Behavior (cont’d.) How species did evolve involves the tentative construction of “evolutionary trees” How species do evolve rests upon some assumptions: Offspring generally resemble their parents for genetic reasons Mutations, recombination, and microduplications of genes introduce new heritable variations Certain individuals successfully reproduce more than others do

The Evolution of Behavior (cont’d.)

The Evolution of Behavior Artificial selection refers to choosing individuals with desired traits and making them parents of the next generation Breeders have produced exceptional racehorses, hundreds of kinds of dogs, chickens that lay huge numbers of eggs. According to Darwin, nature also selects, and successful individuals’ genes will be prevalent in later generations

Artificial Selection

Artificial Selection

The Evolution of Behavior (cont’d.) Common misconceptions about evolution include the following: Lamarckian evolution: “The use or disuse of some structure or behavior causes an increase or decrease in that behavior.” “Humans have stopped evolving.” “Evolution means improvement.” “Evolution acts to benefit the individual or the species.”

Lamarckian evolution

The Evolution of Behavior (cont’d.) Evolutionary psychology focuses upon functional and evolutionary explanations of how behaviors evolved Assumes that behaviors characteristic of a species have arisen through natural selection and provide a survival advantage Examples: differences in peripheral/color vision, sleep mechanisms in the brain, eating habits, temperature regulation

The Evolution of Behavior (cont’d.) Some animal species have better color vision than others, and some have better peripheral vision. Presumably, species evolve the kind of vision they need for their way of life Bears eat all the food they can find, because bears’ main foods—fruits and nuts—are available in large quantities for only short times.

The Evolution of Behavior (cont’d.) Social dominance: The males of many species establish a hierarchy of social dominance through combative encounters. In some species dominant males copulate more than nondominant males and thus are more effective in passing on their characteristics to future generations.

The Evolution of Behavior (cont’d.) Men in most cultures value youth and attractiveness (both indicators of fertility) Women value power and earning capacity more than men do. Physical attractiveness best predicts which women will bond with men of high occupational status.

The Evolution of Behavior (cont’d.) Some behaviors are more debatable regarding the influence of natural selection Examples include: Life span length Altruistic behavior: a behavior that benefits someone other than the actor (e.g. some people donate a kidney to save life of someone they didn’t even know) Altruism is hard to find outside of humans

The Evolution of Behavior A gene only spreads if individuals with it reproduce more than individuals without it Group selection is a controversial hypothesis that states that altruistic groups survive better than less cooperative ones Kin selection is the favored explanation: selection for a gene that benefit’s the individual’s relatives

The Evolution of Behavior (cont’d.) Reciprocal altruism is the idea that individuals help those that will return the favor Building a reputation for helpfulness only works if others are willing to cooperate with you

The Use of Animals in Research Animal research is an important source of information for biological psychology but remains a highly controversial topic Animal research varies on the amount of stress and/ or pain that is caused to the animal itself

Reasons for Animal Research Reasons for studying animals include: The underlying mechanisms of behavior are similar across species and often easier to study in nonhuman species We are interested in animals for their own sake What we learn about animals sheds light on human evolution Some experiments cannot use humans because of legal or ethical reasons

The Ethical Debate Opposition to animal research varies: “Minimalists” favor firm regulation on research and place consideration upon the type of animal used and the amount of stress induced “Abolitionists” maintain that all animals have the same rights as humans and any use of animals is unethical

The Ethical Debate (cont’d.) Justification for research considers the amount of benefit gained compared to the amount of distress caused to the animal No clear dividing line exists Colleges and research institutions in the United States are required to have an Institutional Animal Care and Use Committee Oversees and determine acceptable procedures