The Biology of Behavior PowerPoint® Presentation by Jim Foley © 2013 Worth Publishers Module 5: Genetics, Evolutionary Psychology, and Behavior Topics we were born to learn about Behavior Genetics and Individual Differences Genes: Molecules that code for life Learning about heredity from Twin and Adoption Studies Gene-Environment Interaction Evolutionary Psychology: Adaptive Success Artificial and Natural Selection Critiques of Evolutionary Thinking Behavior Genetics: Predicting Individual Differences More ways of exploring the origins of the biology of behavior: 1. Understanding genes 2. Twin and adoption studies 3. Gene/environment interactions 4. Evolutionary Psychology Behavior geneticists study how heredity and environment contribute to human differences. Let’s start by looking at GENES. GENES: The Building Blocks of Heredity and Development Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. DNA (Deoxyribonucleic Acid) Chromosomes are made of DNA, which are made of genes. Chromosome: threadlike structure made largely of DNA molecules DNA: a spiraling, complex molecule containing genes } Chromosomes and Inheritance The human genome includes 46 chromosomes in 23 sets matched sets; each chromosome has the same gene locations. This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y. A biological parent donates half his/her set of chromosomes to his/her offspring. We received half a set of chromosomes from each biological parent. The Human Genome: 20,000 to 25,000 Genes Human genomes are so nearly identical that we can speak of one universal human genome. Yet tiny genetic differences make a difference. If there is a: .001 percent difference in genome, your DNA would not match the crime scene/you are not the baby’s father. 0.5 to 4 percent difference in genome, you may be a chimpanzee. 50 percent difference in genome, you may be a banana. The genome: an organism’s entire collection of genes How Genes Work Genes are not blueprints; they are molecules. These molecules have the ability to direct the assembly of proteins that build the body. This genetic protein assembly can be turned on and off by the environment, or by other genes. Any trait we see is a result of the complex interactions of many genes and countless other molecules. Next step for behavior geneticists: Controlling Variables Can we design an experiment to keep genes constant and vary the environment and see what happens? Or vary the genes in the same environment? Fraternal and Identical Twins Fraternal “twins” from separate eggs are not any more genetically alike than other siblings. Identical twin: Same sex only Fraternal twin: Same or opposite sex Twin and Adoption Studies To assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment? study traits of siblings vs. identical twins see if the siblings vary more than twins Identical vs. Fraternal Twins Studies of twins in adulthood show that identical twins are more alike than fraternal twins in: personality traits such as extraversion (sociability) and neuroticism (emotional instability). behaviors/outcomes such as the rate of divorce. abilities such as overall Intelligence test scores. Twin and Adoption Studies How do we find out how the same genes express themselves in different environments? We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study). Studies of Identical Twins Raised Apart Similarities found in identical twins despite being raised in different homes: personality, styles of thinking and relating abilities/intelligence test scores attitudes interests, tastes specific fears brain waves, heart rate Critiques of Twin Studies 1. In the more recent years of the Minnesota Twin Family Study, twins have known about each other and may influence each other to be more similar. 2. Coincidences happen; some randomly chosen pairs of people will have similar traits. 3. Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values. BUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins. Searching for Parenting Effects: Biological vs. Adoptive Relatives Studies have been performed with adopted children for whom the biological relatives are known. Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives. Given the evidence of genetic impact on how a person turns out, does parenting/nurture make any difference? Does the home environment have any impact? Parenting Does Matter Despite the strong impact of genetics on personality, parenting has an influence on: religious beliefs values manners attitudes politics habits How does the interaction of genes and environment work? Gene-Environment Interaction: genes turn each other on and off in response to environmental conditions Example in animals: shortened daylight triggers animals to change fur color or to hibernate Epigenetics: The study of how this happens: The environment acts on the surface of genes to alter their activity Example in humans: obesity in adults can turn off weight regulation genes in offspring Evolutionary Psychology: Understanding Human Nature Some topics: Natural selection and adaptation Evolutionary success may help explain similarities Evolutionary psychology is the study of how evolutionary principles help explain the origin and function of the human mind, traits, and behaviors. We have been talking so far about human differences; let’s now seek insight into the ways in which humans are alike. 17 Evolutionary Psychology: Natural Selection: How it Works Begin with a species’ genome, which contains a variety of versions of genes that shape traits. Conditions make it difficult for individuals with some traits (some versions of those genes) to survive long enough to reproduce. Other individuals thus have their traits and genes “selected” to spread in the population. Artificial Selection The Domesticated Silver Foxes Dmitri Balyaev and Lyudmila Trut spent 40 years selecting the most gentle, friendly, and tame foxes from a fox population, and having those reproduce. As a result, they were able to shape avoidant and aggressive creatures into social ones, just as wolves were once shaped into dogs. 19 How might evolution have shaped the human species? Example: Why does “stranger anxiety” develop between the ages of 9 and 13 months? Hint: in evolutionary/survival terms, humans are learning to walk at that time. Infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to stay with parents around the time they learned to walk. 20 Evolutionary Psychology’s Explanation of Biologically Driven Phobias Why do people so easily acquire a phobia of snakes, more easily than a phobia of cars? An evolutionary psychologist would note that snakes are often poisonous… …so, those who more readily learned to fear them were more likely to survive and reproduce. 21 Critiquing Evolutionary Psychology “You’re just taking current reality and constructing a way you could have predicted it.” This is hindsight reasoning and unscientific. Response: yes, but there are predictions made about future behavior using this reasoning. “You’re attributing too much to genes rather than the human ability to make choices about social behavior.” Response: yes, but our evolutionary past does not prevent our ability to act differently; “is” does not equal “ought.” Evolution: Theory Evolution is a scientific theory (NOT a “guess” and not a hypothesis, but something more): a coherent set of principles that fits very well with the accumulated evidence. Parts of the evolutionary story may conflict with other stories of origins and change over time. Is there room for overlap and agreement? Possible areas of consensus, with or without evolution: The human mind and body seems almost “designed,” by evolution or other forces, to have certain traits and abilities. Nurture may shape us, but we seem to start out with some sort of human nature.