Genetic and Evolutionary Foundations of Behavior. Quick Question. Darwin s Theory 2/10/2012. Chapter 3

Transcription

1 Genetic and Evolutionary Foundations of Behavior Chapter 3 Gray, Psychology, 6e Worth Publishers 2010 Quick Question What do you know about Darwin? Come up with as many things as possible. Darwin s Theory 150 years ago, Charles Darwin proposed a theory of evolution that explains both the differences and the similarities between species Today, evolutionary scientists discuss the application of evolutionary theory to explain behavior 1

2 How Genes Affect Behavior Gene for Genes provide the codes for protein Structural proteins Enzymes DNA DNA Composed of a series of amino acids Templates for RNA Genes are segments of DNA Junk DNA Coding genes Regulatory genes Genes Work Only through Interaction with the Environment Environment is every aspect of an individual and his/her surroundings except the genes themselves There is continuous complex interplay between genes and the environment 2

3 Genotype vs. Phenotype Genotype The set of genes that an individual inherits Phenotype Observable properties of the body and behavioral traits How Genes Are Passed Along through Reproduction DNA exists in chromosomes The normal human cell has 23 chromosome pairs All humans have 22 of these pairs; the last pair is sex chromosomes (XX for females, XY for males) One member of each of these pairs comes from one parent, the other member of the pair comes from the other parent Mitosis and Meiosis Mitosis When cells (other than reproductive cells) divide to create identical cells Meiosis Reproductive cells replicate and divide many times to create non-identical cells 3

4 Genetic Diversity of Offspring Genes have a better chance of survival if they are rearranged at each generation Twins are the only offspring that are not diverse Identical twins Fraternal twins Why do you think it would be advantageous to have genes rearrange each generation? Are you a twin? Do you know any twins? Do you think twins would act differently if they grew up apart? Homozygous and Heterozygous When two genes at the same locus on a pair of chromosomes are the same, the individual is homozygous at that locus When the two genes are not the same, the individual is heterozygous at that locus Dominant and Recessive Genes A dominant gene is one that will produce its observable effects in either the homozygous or heterozygous condition A recessive gene is one that will only produce its observable effects in the homozygous condition 4

5 Mendelian Pattern of Heredity Mendel came up with the idea that genes come in pairs, and that one can be dominant over the other He discovered that some behaviors are affected by a single gene Fearfulness in dogs KE family language disorder Selective Breeding Modifying a specific behavior or characteristic by mating individuals with or without the specific characteristics Example Tryon s classic maze rats Do you think certain dog breeds have been selectively bred for aggression? How much of an influence do you think the environment has on the dog s aggression? Polygenic Behavioral Characteristics Many human behaviors are complex and are affected by multiple genes and interactions with the environment Do you think science will ever get to the point that we can breed out undesirable characteristics in humans (for example, murder)? 5

6 Questions? Comments? Evolution by Natural Selection Origin of Species Artificial selection Human-controlled selective breeding Natural selection Selective breeding in nature Darwin s essential point: Individuals of a species vary in the number of offspring they produce Traits that increase # of offspring will be selected for Traits that decrease # of offspring will be selected against Genetic Diversity Provides the Fodder for Natural Selection There are two sources of the genetic variability on which natural selection acts Reshuffling of genes during reproduction Mutations Errors that occasionally and unpredictably occur during DNA replication In the movie X-MEN, a mutation causes certain people to develop extraordinary powers. Do you think anything like that could happen in real life? Why or why not? 6

7 Environmental Change Provides the Force for Natural Selection Evolution is spurred by environmental changes Environment can cause appropriate mutations that change and promote natural selection Grant and Grant s work on finches What do you think would happen to the evolution of the polar bear if the snowcovered ground became rock-covered ground? Evolution Has No Foresight Evolutionary paths are not working toward some predetermined end Humans are not the most evolved species Natural selection is not a moral force Natural Selection as a Foundation for Functionalism Functionalism: The attempt to explain behavior in terms of what it accomplishes for the behaving individual Tries to answer how a trait helped ancestral members of the species survive and reproduce 7

8 Ultimate and Proximate Explanations Ultimate explanations Functional explanations at the evolutionary level Proximate explanations Explanations that deal with the mechanism in the immediate conditions Example: Songbirds Limitations on Functionalist Thinking Some traits are vestigial Some traits are side effects of natural selection for other traits Some traits result from chance Evolved mechanisms cannot deal effectively with every situation Species-Typical Behaviors in Humans Human emotional expression Darwin Ekman and Friesen Eibl-Eibesfeldt Role of learning in developing species-typical behavior Biological preparedness and species-typical behavior 8

9 Cross-Species Comparisons Homologies Physical mechanisms of behavior Evolutionary pathways of species-typical traits Analogies Convergent evolution Evolutionary Analyses of Mating Patterns Mating is what drives evolution Four classes of mating arrangements Polygyny Polyandry Monogamy Polygynandry Mating Patterns and Parental Investment Parental investment: Time, energy, and risk to survival involved in producing, feeding, and caring for offspring Trivers (1972): In general, for species in which parental investment is unequal, the more parentally invested sex will be more vigorously competed for and more discriminating when choosing mates 9

10 Emotions and Human Mating Human mating is mostly monogamous and partly polygamous Romantic love and mating Jealousy and mating What would upset you more: Your partner having sex with someone else, but definitely not forming an emotional bond, or your partner forming an emotional bond with someone else, but definitely not having sex? Evolutionary Analyses of Helping and Hurting: Aggression Sex differences in aggression Male violence in humans Female bonobo domination What do you think: Are women the weaker sex? What if we measure aggression not as physical aggression, but as emotional aggression? Evolutionary Analyses of Helping and Hurting: Cooperation Helping Cooperation Altruism Kin selection theory Reciprocity theory Think about the people you are most likely to help? Are you more likely to help someone who is related to you or someone who will help you later? 10

11 Fallacies to Avoid Naturalistic fallacy Natural = moral = right Social Darwinists Deterministic fallacy Genes determine behavior Many people believe that if evolution is true, it means that only healthy people will survive. How can you explain that today many sick and disabled people survive and live as well as healthy people? Assessment What was the most important concept or idea you learned from this chapter? 11