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INTRODUCTION TO PSYCHOLOGY Chapter 2 Evolution and the Biological Roots of Behavior At the end of this Chapter you should be able to: Learn about evolutinary roots of motivated behavior Understand the achievement of Homeostatis Learn about Eating Learn about Threat and Agression Learn about Mating Charles Darwin Rattled the world with his theory of natural selection Wrote “Origin of Species” Natural Selection The Origin of Species Finches developed gene mutation Advantage over peers More successful reproduction Evolve to look different than species in different environments How are these characteristics passed on? How and why do traits evolve over time? Gregor Mendel (1822-1884) Studied pea plants How characteristics change over generations Set the framework for what we know today. What do we know today about how characteristics are passed through generations? Chromosomes Structures in the nucleus of each cell that contain genes Hold 1,000 or more genetic commands Genes Complex molecules Provide basic blueprints as organisms mature from a fertilized cell. DNA (deoxyribonucleic acid) The complex molecule that is the constituent of genes Controls production of proteins and enzymes that make up the body Chromosomes Come in pairs; from Mom and Dad Corresponding gene pair Dominant-exerts effect regardless of correponding gene Recessive-exerts effect only if corresponding gene matches Do not directly influence how we look, etc. Controls enzyme and protein production Enzymes and proteins influence our overall make up Genotype –genetic blueprint determined by chromosomes Phenotype –organism’sactual characteristics Human Behavior Homeostasis Eating Threat and Aggression Mating Homeostasis Another area where biological perspective is helpful in understanding behavior: Examining the mechanisms of HOMEOSTASIS and how they affect our behavior Every organism has both an external and an internal environment. Homeostasis: maintenance of the internal environment of the organism (concentrations of various salts in the body’s fluids, the dissolved oxygen levels, the quantities of nutrients like glucose etc) Outside environment may fluctuate, but internal environment remains stable Homeostasis involves many mechanism; including those that rely on “negative feedback”. Ex: Home heating systems: A thermostata turns on the heater when the house’s temperature falls below a given setting. The heater than causes the house’s temperature to rise, and this rise serves as a negative feedback for the thermostat. When the house reaches the present temperature, the thermostat turns the heater off. The Nervous System All mammals (and all birds) are endotherms; organisms that maintain stable body heat. Endothermic animals sometimes become too warm ; and so need to lose heat and sometimes too cold and so preserve the heat created by their own metabolic activity These two activities are controlled by the autonomic nervous system Autonomic Nervous System Central Nervous System (CNS) The brain and spinal cord Peripheric Nervous System (PNS) System of nerves outside of the brain and spinal cord Send control to the glands and smooth muscles Controls internal organs, usually not under voluntary control The peripheral nervous system is subdivided into two: sensory-somatic nervous system and the autonomic nervous system Autonomic Nervous System Governed by the hypothalamus Two branches Sympathetic Parasympathetic Sympathetic Nervous System Triggered when body temperature is too low Revives up body activity to prepare for rigorous activity Increased heart rate Slowing down of peristalsis (rhythmic contractions of intestines), so not using energy during digestion Vasoconstriction Contraction of skins capillaries Parasympathetic Nervous System Triggered when body’s temperature is too high Restored body’s internal activities Cardio slowing Speeds up peristalsis Vasolidation Widening of skin’s capillaries Stimulus Body prepares for response Body returns to normal Human Behavior Eating Built-in system for regulating food intake Maintain genetically determined set points; a weight the body tries to maintain (the target) Liver Hypothalamus Stomach and Duodenum Adipose Tissue Maintains constant level of glucose in bloodstream Liver Too much glucose detected… Glucose turns into glycogen and fatty acids Liver signals to stop eating Not enough glucose detected… Stored glycogen and fatty acids turn back into glucose Liver signals to eat Hypothalamus Contains glucoreceptors Also sensitive to glucose levels in the blood Sends signals similar to that of the liver Stomach and Duodenum Contains receptors sensitive to nutrients dissolved in digestive juices Stops signaling hunger when proper nutrients are on the way Adipose Tissue Stores fat in cells to be used when glycogen runs out Secretes leptin when cells are full Chemical that indicates when no more fat storage is needed Inhibits appetite stimulants Such as neuropeptide Y (NPY) Why so many signals? Safety provided by backup systems If one system fails, the organism is still protected Different signals monitor different aspects of our nutritional needs Leptin-longer term needs Others (cues from stomach)-hour-by-hour energy requirement variations Aside from our internal structures, what else can influence what and when we eat? Immediate outside influences Culture Social Cognitive Obesity Obesity is an eating disorder. We need to consider multiple factors if we want to understand eating behavior. Is it because we eat too much? Some people are predisposed to obesity due to their individual genetic pattern (i.e., set points). Threat and Aggression What happens biologically when we feel threathened? Self-protection Internal adjustments necessary to respond to threat in environment When threat detected: Sympathetic branch of ANS activated Prepares body for immediate, intense activity. Surge of adrenaline released Male aggression and hormones: The male is the far more aggressive sex. This gender difference holds only for physical aggression. Testosterone (the male sex hormone) is associated with physical aggressiveness in many species. Male versus female aggression: Males use physical aggression (pushing and punching). Females use social aggression (spreading gossip and rumors, isolating unwanted friends). Learning to be aggressive? 1. Explicit learning: someone demands or teaches us 2. Implicit: we observe 3. Seems to be causal; when we observe violence, we become violent Is aggression inevitable? Cultural values, testosterone, defending your territory, revenge etc... If your opponent is stronger than you are, then you better not start the battle at all! This is a limit on aggression. Dominance hierarchy: who is the strongest in the group? Assigned status is a limit on aggression. Nature-Nurture Debate Relative importance of an individual's innate qualities (“nature”) versus personal experiences (“nurture”) in determining individual differences in behavioral traits. Mating Appearance Matching Gender Differences Appearance Humans value attractiveness in a partner Who is attractive? Isn’t beauty the eye of the beholder? Facial Appereance Cross-culturally Shiny hair No visible deformities Clear skin Symmetrical face Average face (slight deviation can help) Developmentally Infants Infants as young as 3-months-old look longer at adult-rated attractive faces 12-month-olds interact more positively with adult wearing “attractive” mask. Why is there a preference for attractiveness? Indication of health Body Appearance Women Not size Waist-to-hip ration Mature pelvis adequate fat supply Fertility and readiness for pregnancy Not a strong relationship between facial attractiveness and health The Matching Hypothesis There is a strong correlation between the level of attractiveness of two partners Prefer partners similar to themselves The Matching Hypothesis Attractiveness Personality Race Ethnic origin Social status Education level Family background Income Religion Habits Gender differences in mate selection / Animals Females Decide when to mate and mating partner Most physical investment in breeding Males Advertise sexual availability Gender differences in mate selection / Humans Man seeking woman… Physical attractiveness Healthy and fertile Youth More reproductive years Kindness Intelligence Less value of commitment More jealous by sexual disloyalty Women seeking men… Older Social and financial status Better ensures offspring’s survival Kindness Intelligence More value of commitment More jealous of emotional disloyalty Contribution of Biological Perspective Biological perspective: much to teach us about mechanisms, evolutionary influence on behaviors No aspect fully explained by biological perspective Focus thus far: large scale processes/mechanisms
