Historical Underpinnings In questions about epistemologies, or where knowledge bases come from: Plato (Rationalism) Knowledge we gain by ‘learning’ is just a recollection of knowledge we’re born with. Descartes (Nativism) Knowledge is innate. Locke (Empiricism) Knowledge comes from experience. Watson (Behaviorism) Knowledge [& behaviors] are learned through experience.
After each student writes this down, ask class what characteristics were in each column?
Although they have the same parents, siblings differ from each other in many ways, such as eye color, height, and personality. This occurs because each has a specific combination of genes that differ in part due to random cell division that occurs prior to reproduction. Reproductive cells from each parent divide to produce gametes , egg and sperm cells, that contain only one half of each pair of chromosomes. The sperm and egg cells then combine during fertilization. One half of each parent’s chromosomes join in a random fashion. The fertilized cell, known as a zygote , contains 23 pairs of chromosomes, one half of each pair from the mother and the other half from the father. The evolutionary significance of these changes in adaptiveness is complex, but mutations that lead to abilities or behaviors that are advantageous to an organism may spread through the gene pool because those who carry the gene are more likely to survive and reproduce. For instance, consider industrial melanism , in which areas of the world with heavy soot or smog tend to have moths and butterflies that are darker in color. Prior to industrialization, darker insects were more likely to be spotted against pale backgrounds. Any mutation that led to darker coloring was quickly eliminated through natural selection. But, with industrialization, pollution led to a darkening of trees and buildings, and therefore darker-colored insects became more adaptive. You may wonder how genetic mutations lead to disease and why they remain in the gene pool. For instance, sickle-cell disease is a genetic disorder that mostly affects African Americans and alters how oxygen is processed in the bloodstream; it can lead to pain, physical damage, and anemia. The gene for the disease is recessive, so that most carriers have healthy phenotypes in spite of genotypes that contain the disease. Thus, only those who inherit recessive genes from both parents will develop the disease. Recessive genes do not interfere with health in most people, which allows them to survive in the gene pool. In addition, the gene for sickle-cell disease also increases resistance to malaria, and therefore in environments in which malaria is prevalent, such as certain regions in Africa, the sickle-cell gene has some benefit. In contrast to recessive genes, most dominant gene disorders are lethal for most of their carriers and therefore do not last in the gene pool.
Twin studies compare similarities between different types of twins to determine the genetic basis of specific traits. Monozygotic twins , also called identical twins, are the result of one zygote dividing into two, each having the same chromosomes and the genes they contain. Dizygotic twins , sometimes called fraternal or nonidentical twins, are the result of two separately fertilized eggs and are no more related than any other pair of siblings. To the extent that monozygotic twins are more similar on a given dimension than dizygotic twins, the increased similarity is considered most likely due to genetic influence. Of course, even identical twins do not have the exact same environment (and in rare circumstances might even have different genes due to random mutations), and therefore they have different phenotypes, but they are typically more similar than dizygotic twins, who differ both in genotype and phenotype. Heredity is the transmission of characteristics from parents to offspring by means of genes. A term that is often confused with heredity, but that means something else altogether, is heritability , which is a statistical estimate of the portion of observed variation in a population that is caused by differences in heredity. Variation is the measure of the overall amount of difference among people. This variation is estimated based on studies of twins and other methods. If a trait such as height has a heritability of .60, it means that 60 percent of height variation among individuals is genetic, not that you get 60 percent of your height from genetics and 40 percent from your environment. Heritability refers to populations, not to individuals. LOOKING AHEAD: PERSONALITY DISPOSITIONAL FACTORS, like friendliness, irritability, optimism, pessimism, introversion, sociability, intelligence, will tend to show heritability coefficients ranging from .40--.60, which, in turn, can be interpreted to mean that 40-60 percent of variation in critical personality variables is genetic across individuals SO-THAT, STATISTICALLY , THE MAIN POINT TO MAKE TO YOUR STUDENTS IS THAT HERITABLITY REFERENCES A POPULATION ESTIMATE AND TELLS US NOTHING ABOUT THE PROPORTION OF GENTIC CONTRIBUTION THAT HAS BEEN MADE IN A TRAIT-CHARACTERISTIC IN THE CASE OF ANY PARTICULAR INDIVIDUAL ( E.G, YOURSELF, YOUR MOM, YOUR GRANDPARENTS AND COUSINS AND YOUR FRIENDS). THE OTHER SIDE OF THE STORY OR COIN IS OF COURSE THAT ANOTHER 40-60 PERCENT OF THE TRAIT VARIANCE CAN BE ATTRIBUTED TO ENVIRONMENT, THUS MAKING THE CASE FOR THE ROLE OF ENVIRONMENTAL ATTENTION TO STRESS, TO EDUCATIONAL RESOURCES, TO LEARNING EXPERIENCES, TO CULTURAL INFLUENCES, TO NEIGHBORHOODS AND FRIENDS. It is also important to point out that the population used to estimate total variation can affect the estimate obtained for heritability. Typically, the more diverse the population, the lower the estimate of heritability. This occurs because of the increased variability that comes from diversity and because the estimates of the genetic variation do not consider such diversity. The important point is that heritability is an estimate that is not precise and that can be affected by a number of factors. Still, it helps behavioral geneticists in clarifying the interaction between the environment and genes, so that they can understand the circumstances in which genes operate.
Born in 1940, Jim Springer and Jim Lewis were adopted by different families. In 1979, psychologist Thomas Bouchard, interested in the nature/nurture debate, began a detailed investigation of identical twins who were separated at birth. The Jim twins caused a public stir early in this study, as they shared remarkably similar lives. Aside from the fact that they were both named Jim by their adoptive parents, the twins had both married twice - the first time to women named Linda and the second to women called Betty. Jim Springer named his son James Allen whilst Jim Lewis called his son James Alan. They both had dogs named Toy, both spent time as sheriff's deputies, they drank the same beer, smoked the same cigarettes and drove the same model of car. Tempting as it may be to view the twins' case as evidence of something spooky, many of these similarities are not unlikely. Jim is a very common name, and so was the model of car they both drove. Class exercise on similarities What’s probability that two people have the same birthday in a class of 40? Most people say it’s very low, but actually it’s about a 90% chance. Go through class to check.
Same placenta identical twins more alike than different placenta twins.
According to some researchers, the dismal conditions of the slave trade may have led to a change in the genetic constitution of African Americans (Wilson & Grim, 1991). As many as one in four slaves died during transportation, and approximately the same number died within the first few years of arrival in America. Wilson and Grim argue that the horrific conditions imposed a strong selection factor in determining the type of individual who was able to survive. Those slaves who were able to maintain high blood pressure on low levels of salt might have been more likely to survive. In contemporary times, however, with salt readily available, a greater sensitivity to salt may cause African Americans to become salt hypertensive. The theory is provocative and difficult to test, but it highlights one possible way in which social context can affect genetic constitution.
PAGE 85: … researchers followed a group of more than 1,000 New Zealanders from their births in 1972–1973 until adulthood, …. … You will read about MAO in Chapter 13; for now it is sufficient to know that low levels of MAO have been implicated in aggressive behaviors. The gene for MAO comes in two forms, one of which leads to higher levels of MAO and one of which leads to lower levels. Caspi and colleagues (2002) found that boys with the low-level MAO gene appeared to be especially susceptible to early childhood maltreatment. Those children who were mistreated and had the low-activity MAO gene were much more likely to be convicted of a violent crime than those with the high-activity gene. Indeed, although only 1 in 8 boys was mistreated and had the low MAO gene, they were responsible for nearly half of all violent crimes committed by the group (Figure 3.6).
Lecture 6 Genetics.ppt
The Nature/Nurture Debate <ul><li>How great is the influence of genes or environment on our behavior, personality, biology, etc.? </li></ul>
The Nature Nurture Debate <ul><li>Make two columns on a sheet of paper - 1) nature; 2) nurture </li></ul><ul><li>Write characteristics you believe are mostly nature or mostly nurture in the appropriate column </li></ul><ul><li>If the characteristic was nurture, what seemed to be the influences? </li></ul>
Genes: Essential Definitions <ul><li>Chromosomes </li></ul><ul><ul><li>threadlike structures made of DNA that contain the genes </li></ul></ul><ul><li>DNA (deoxyribonucleic acid) </li></ul><ul><ul><li>complex molecule containing the genetic information that makes up the chromosomes </li></ul></ul><ul><ul><li>has two strands-forming a “double helix”- held together by bonds between pairs of nucleotides </li></ul></ul>
Genes: Essential Definitions <ul><li>Genes </li></ul><ul><ul><li>biochemical units of heredity that make up the chromosomes </li></ul></ul><ul><ul><li>a segment of DNA capable of synthesizing a protein </li></ul></ul><ul><ul><li>The paradox 30,000 genes for 300,000 proteins </li></ul></ul><ul><li>Genome </li></ul><ul><ul><li>the complete instructions for making an organism </li></ul></ul><ul><ul><li>consisting of all the genetic material in its chromosomes </li></ul></ul>
Genes: Essential Definitions <ul><li>Genotype </li></ul><ul><li>-The genetic constitution of an individual. Depending on context, this may refer to the alleles at a single locus or to the complete set of genes. </li></ul><ul><li>Phenotype </li></ul><ul><li>-Any measurable trait of an individual. Phenotype results from an interaction between genotype and environment. </li></ul>
Genotypic Variation Is Created by Sexual Reproduction <ul><li>What determines the genetic uniqueness of individuals? </li></ul><ul><ul><li>Gametes </li></ul></ul><ul><ul><li>Zygote </li></ul></ul><ul><li>Mutations are experiments in selective advantage </li></ul><ul><ul><li>Industrial melanism </li></ul></ul><ul><ul><li>Sickle-cell disease </li></ul></ul>
<ul><li>- homozygotes </li></ul><ul><ul><li>anemia, joint pain, swollen spleen, frequent severe infections, high rate of childhood death </li></ul></ul><ul><li>- heterozygotes </li></ul><ul><li>- basically normal blood function </li></ul><ul><li>- resistant to malaria </li></ul><ul><li>Price for malarial resistance </li></ul><ul><li>- homozygous sickle cell children </li></ul>Sickle Cell Disease and Malaria
Sexual Reproduction <ul><li>Combines gametes thereby creating new genotype </li></ul><ul><li>May have evolved to outcompete parasites </li></ul>
Behavior Genetics <ul><li>Identical Twins </li></ul><ul><ul><li>develop from a single zygote (fertilized egg) that splits in two, creating two genetic replicas </li></ul></ul><ul><li>Fraternal Twins </li></ul><ul><ul><li>develop from separate zygotes </li></ul></ul><ul><ul><li>genetically no closer than brothers and sisters, but they share the fetal environment </li></ul></ul>Identical twins Fraternal twins Same sex only Same or opposite sex
Identical (monozygotic twins) Non-identical, fraternal (dizygotic twins) Identical twins reared together same genes (relatedness of 1.0) same environment Identical twins reared apart sane genes (relatedness of 1.0) different environment Fraternal twins reared together half genes the same (relatedness 0.5) same environment Fraternal twins reared apart half genes the same (relatedness 0.5) different environment Nature v Nurture: Twin Studies
Jack Yufe: raised by Jewish father in Caribbean Oskar Stohr: raised by catholic grandmother in Nazi Germany Nature v Nurture: Twin Studies If we had identical twins reared apart could we separate the effects of phenotype, of genotype, and of the environment. In some cases this has happened.
Nature v Nurture: Twin Studies Both like sweet liqueurs Store rubber bands on their wrists Read magazines from back to front Dip buttered toast in their coffee Have very similar personalities
Social and Environmental Contexts Influence Genetic Expression <ul><li>African Americans and Hypertension: a controversial theory </li></ul><ul><li>Gene expression as concerns child maltreatment and criminality is reflected in next slide. </li></ul>
Temperament and genetics <ul><li>Suomi genetic studies on rhesus monkeys </li></ul><ul><ul><li>Two alleles of one gene: </li></ul></ul><ul><ul><ul><li>the “short” version causes neurobehavioral deficits ONLY IF the infant monkey is raised with peers but without its mother </li></ul></ul></ul><ul><ul><ul><li>The “long” version causes no neurobehavioral deficits, regardless of rearing </li></ul></ul></ul><ul><ul><li>Maternal buffering? </li></ul></ul>
Behavior Genetics <ul><li>Adoption studies </li></ul><ul><ul><li>Are adopted kids more like their biological relatives or their adopted relatives? </li></ul></ul><ul><ul><li>General findings: adoptees more like biological parents than adopted parents in intelligence and personality/temperament </li></ul></ul>