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CHAPTER 3: Genetic and Evolutionary Foundations of Behavior Why Genetics? •Behavior is hereditary! •Our environment has shaped our behavior across generations EVOLUTION •We can learn much about our behavior by studying our animal relatives •Did you know: we share 98.8% of our genes with chimpanzees? •50% with a banana How Genes Affect Behavior GENE: the basic physical unity of heredity Genes code for protein molecules Structural proteins Enzymes – control the rate of every chemical reaction in every cell Genes are composed of long molecules called DNA (deoxyribonucleic acid) From Cells to Genes… chromosome DNA cell gene nucleus Genes Provide the Code for Proteins Proteins are comprised of amino acids Coding vs. “junk” DNA CODING GENES: code for unique protein molecules REGULATORY GENES: help activate or suppress specific coding genes and thereby influence the body’s development Genes do not “code for” behaviors. Gene/Environment Interaction ENVIRONMENT: every aspect of an individual and his or her surroundings except the genes themselves. Geneticists use the term genotype to refer to the set of genes that the individual inherits and the term phenotype to refer to the observable properties of the body and behavioral traits. Genes and Replication: Mitosis MITOSIS: the form of cell division involved in normal body growth, which produces cells that are genetically identical to each other MEIOSIS: The form of cell division involved in producing egg or sperm cells, which results in cells that are genetically dissimilar and that each have half the number of chromosomes of the original cell. The Genetic Diversity of Offspring ZYGOTE: The single cell that is formed when an egg and sperm cell unite Consequences of Gene Pairing LOCUS: a position on a chromosome that contains the DNA of a single gene ALLELES: different genes that can occupy the same locus on a pair of chromosomes and can potentially pair with one another Homozygous vs. heterozygous Dominant vs. recessive Consequences of Gene Pairing Mendelian Genetics Gregor Mendel, Mid-19th Century Mendelian Genetics Polygenic Characteristics POLYGENIC CHARACTERISTICS: any trait or characteristic for which the observed variation is affected by many genes SELECTIVE BREEDING: the mating of those members of a strain of animals or plants that manifest a particular characteristic to affect the genetic makeup of future generations of that strain Evolution by Natural Selection NATURAL SELECTION: selective breeding that results from the obstacles to reproduction that are imposed by the natural environment Genetic Variability • Genes are reshuffled during DNA recombination and meitotic division • Errors that occasionally and unpredictably occur during DNA replication, producing a “replica” that is different from the original Environmental Influence on Natural Selection Evolution is contingent on environmental change Evolution can progress slowly, rapidly, or almost not at all More complex changes require much more time All species are to varying degrees similar to one another because of common ancestry, and all species are to some degree unique because natural selection has adapted each species to the unique aspects of the environment in which it lives and reproduces. Evolution in Action Before the industrial revolution, a uniformly dark variant of the peppered moth made up 2% of the species. After the industrial revolution, 95% of peppered moths showed this dark coloration. Skinks living on the coast tend to lay eggs. Those skinks living in the cooler mountains tend to give birth to live young. The Blue Moon Butterfly of the Samoan islands was being attacked by a parasite which destroyed male embryos. This led to a gender imbalance whereby males made up only 1% of the butterfly population. However, within ten generations (~1 year) males had returned to 40% of the population. Over time the bacteria have become far more efficient at growing under the conditions used. One of the populations developed the ability to utilize citrate as a nutrient. • Malaria • MMR Mistaken Beliefs about Evolution Functionalism FUNCTIONALISM: a school of psychological thought, founded by William James and others, that focuses on understanding the functions, or adaptive purposes, of mental processes. • Why do giraffes have long necks? • Why do male songbirds sing? • Why do humans have the ability to learn language? Functionalistic Explanations of Behavior Ultimate Explanation Proximate Explanation Functional explanations at the evolutionary level; that is, how the behavior plays or played a role in survival and reproduction Explanations that deal with the immediate environmental conditions or the mechanisms within the individual that cause the behavior to occur Limitations on Functionalist Thinking 1. VESTIGIAL CHARACTERISTICS: inherited characteristics of anatomy or behavior that are no longer useful to the species but were presumably useful at an earlier time in evolution • 2. E.g. appendix, grasp reflex Some traits are side effects of natural selection for other traits Limitations on Functionalist Thinking 3. Some traits result simply from chance • Variation due to chance alone without selection is known as GENETIC DRIFT 4. Evolved mechanisms cannot deal effectively with every situation Species-Typical Behaviors in Humans • Any behavior pattern that is so characteristic of a given species of animal that it can be used to help identify that species • However, these behaviors are not rigid and uninfluenced by learning! The Role of Learning in SpeciesTypical Behaviors Walking Language Biological Preparedness BIOLOGICAL PREPAREDNESS: organisms have physical and anatomical structures that predispose them to engage in certain (species-specific) behaviors The environment also plays a role! Cross-Species Comparisons of Species-Typical Behaviors HOMOLOGY: any similarity among species that exists because of the species’ common ancestry Cross-Species Comparisons of Species-Typical Behaviors ANALOGY: any similarity among species that is not due to common ancestry but has evolved independently because of some similarity in their habits or lifestyles Evolutionary Origin of Two Human Smiles Evolutionary Analyses of Mating Patterns • One male mates with more than one female • One female mates with more than one male • One male mates with one female • Members of a group consisting of more than one male and more than one female mate with one anther Parental Investment The time, energy, and risk to survival involved in producing, feeding and otherwise caring for each offspring In general, for species in which parental investment is unequal, the more parentally invested sex will be (a) more vigorously competed for than the other and (b) more discriminating than the other when choosing mates Mating Patterns and Parental Investment POLYGYNY • High female and low male parental investment • Females choose the best males • Males must try and mate with as many females POLYANDRY • High male and low female parental investment • Tend to be egg layers • Females are more aggressive courters Human Mating Patterns Humans fall on the boundary between monogamy and polygyny Long-term mating bonds Sex Differences in Aggression AGGRESSION: fighting and threats of fighting among members of the same species In primates, males are more aggressive than females These behaviors are advantageous (evolution is not a moral force) Violence in Humans Humans are no exception to aggression and violence Cross-culturally, men are more aggressive than women (sexual jealousy) Exception: female bonobos Patterns of Helping HELPING: any behavior that increases the survival chance or reproductive capacity of another individual COOPERATION: a type of helping behavior in which interaction among two or more individuals increases the survival chance or reproductive capacity of each individual involved in the interaction E.g. living in groups or colonies Altruism ALTRUISM: a type of helping behavior in which an individual increases the survival chance or reproductive capacity of another individual while decreasing its own survival chance or reproductive capacity Kin Selection Theory of Altruism Apparent acts of altruism have come about through natural selection because such actions are disproportionately directed toward close genetic relatives and thus promote the survival of others who have the same genes Reciprocity Theory of Apparent Altruism Apparent acts of altruism have come about through natural selection because they are actually forms of long-term cooperation rather than true altruism Evolutionary Fallacies Naturalistic Fallacy Deterministic Fallacy The mistaken belief that whatever is natural (and particularly whatever is a product of natural selection) is right, good or moral The mistaken belief that genes control, or determine, behavior in a manner that is independent of environmental influences Morality is a product of the human mind! Beware the phrase “more evolved” We humans can control our environment and thereby control ourselves!