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Untangling Nature and Nurture Behavior Genetics: the study of the interaction of genes and environment on behavior Nature vs. Nurture “Nature” = the role that genes have on a trait “Nurture” = the role that life experience has on a trait. Sometimes, it is surprising. Genes: Our Biological Blueprint Chromosomes threadlike structures made of DNA that contain the genes DNA (deoxyribonucleic acid) complex molecule containing the genetic information that makes up the chromosomes has two strands-forming a “double helix”--held together by bonds between pairs of nucleotides Genes: Our Biological Blueprint Genes biochemical units of heredity that make up the chromosomes a segment of DNA capable of synthesizing a protein Genome the complete instructions for making an organism consisting of all the genetic material in its chromosomes Genes: Their Location and Composition Nucleus Cell Chromosome Gene DNA Evolutionary Psychology Natural Selection the principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations Mutations random errors in gene replication that lead to a change in the sequence of nucleotides Evolutionary Psychology Evolutionary Psychology the study of the evolution of behavior and the mind, using the principles of natural selection Gender in psychology, the characteristics, whether biologically or socially influenced, by which people define male and female Evolutionary Psychology Men preferred attractive physical features suggesting youth and health Women preferred resources and social status Behavior Genetics Behavior Genetics study of the relative power and limits of genetic and environmental influences on behavior Environment every nongenetic influence, from prenatal nutrition to the people and things around us Behavior Genetics Identical twins Fraternal twins Identical Twins develop from a single fertilized egg that splits in two, creating two genetically identical organisms Fraternal Twins Same sex only Same or opposite sex develop from separate eggs genetically no closer than brothers and sisters, but they share the fetal environment Epigenetics • Often nature and nurture interact • Overkalix study – Famine in 1944 – Grandpa exposed to famine as preadolescent = low cardiovascular deaths of grandsons – Grandpa NOT exposed to famine as preadolescent = high diabetes mortality in grandsons. – Granddaughters of women who experience famine while in the womb died earlier. Environmental factors can alter the expression of genes. These changes are called “epigenetic tags”. Heritability • The percentage of trait variation in a group that can be attributed to genetic differences • Depends on the population Heritability Sara is very outgoing and agreeable Suzy is timid and nonconforming If this pair of IDENTICAL twins is my population, what percent of the personality differences is attributable to genetic differences between them? The heritability is 0%. Heritability Joe and Hank are not related. At birth, both were placed in identical environments that were maintained identical until they were 10 years old. At 10, Joe is outgoing and friendly. At 10, Hank is withdrawn and shy. In this (very small) population, what is the heritability of their personality traits? In other words, what percentage of the difference is attributable to genes? 100% How heritable is that trait? Trait Population Creativity Extraversion Autism Depression Sleep quality TV viewing Religious beliefs adolescents adults general general general 3-5 year olds general women general women Religious conservatism Divorce Height Heritability 25% 30-50% 90-95% 40-55% 35% 10-45% 0% 40% 55% 92% http://www.peele.net/lib/genes.html The Stanton Peele Addiction Website Behavior Genetics Temperament a person’s characteristic emotional reactivity and intensity Heritability the proportion of variation among individuals that we can attribute to genes may vary, depending on the range of populations and environments studied Behavior Genetics Interaction the dependence of the effect of one factor (such as environment) on another factor (such as heredity) Molecular Genetics the subfield of biology that studies the molecular structure and function of genes Environmental Influence Two placental arrangements in identical twins Environmental Influence Experience affects brain development Impoverished environment Rat brain cell Enriched environment Rat brain cell Environmental Influence A trained brain Environmental Influence Culture the enduring behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted from one generation to the next Norm an understood rule for accepted and expected behavior Environmental Influence Personal Space the buffer zone we like to maintain around our bodies Memes self-replicating ideas, fashions, and innovations passed from person to person Examples of Influence by Age Drinking Age? Differs by culture Dating Age? Differs by culture Sexuality Age? Adulthood Age? Differs by culture Working Age? Differs by culture leaving school Differs by culture Age? Differs by culture Marriage Age? Differs by culture Drinking Age • The average (mean) minimum legal drinking age around the globe is 15.9. The majority of countries have set the drinking age at 18. In fifty countries the minimum age is lower than 18 and in 12 countries it is higher than 18. • The enforcement of minimum legal drinking ages also varies widely between countries and often within countries. In many nations the law isn’t generally enforced unless alcohol is abused and associated with behavioral problems. • Internationally, the average age at which drinking alcohol first occurs is 12 years and about 80% of young people begin drinking alcoholic beverages regularly at age 15 or younger according to the World Health Organization (WHO). Dating Age • Ranges around the world. • India, Japan, China- Most (some suggest 9 of 10) arranged • Sweden- Most start around 10-11. • U.S. – 15-17 Sexuality The Nature and Nurture of Gender X Chromosome the sex chromosome found in both men and women females have two; males have one an X chromosome from each parent produces a female child Y Chromosome the sex chromosome found only in men when paired with an X chromosome from the mother, it produces a male child The Nature and Nurture of Gender Testosterone the most important of the male sex hormones both males and females have it additional testosterone in males stimulates growth of male sex organs in the fetus development of male sex characteristics during puberty Role a set of expectations (norms) about a social position defining how those in the position ought to behave The Nature and Nurture of Gender Gender Role a set of expected behaviors for males and females Gender Identity one’s sense of being male or female Gender-typing the acquisition of a traditional masculine or feminine role The Nature and Nurture of Gender Gender and Culture The Nature and Nurture of Gender The Nature and Nurture of Gender Social Learning Theory theory that we learn social behavior by observing and imitating and by being rewarded or punished Gender Schema Theory theory that children learn from their cultures a concept of what it means to be male and female and that they adjust their behavior accordingly The Nature and Nurture of Gender Two theories of gender typing Twin Studies Identical Twins v. Same genes, Same environment Fraternal Twins Different genes, Same environment Therefore, greater differences between the two groups indicate greater heritability (“Nature”). The trait might appear to have a large genetic component. Twin Studies Increased risk of schizophrenia if twin develops disease 60% % increase 50% 40% 30% 20% 10% 0% Fraternal twins Identical twins Criticism: 1) Do fraternal twins really have equally similar environments to identical twins? Differences in looks or inborn temperament may cause people to treat you differently. 2) Identical twins may share a placenta but fraternal twins do not. Thus, we can’t eliminate prenatal environments as the cause of the differences between the two groups. Twin Studies Identical Twins Reared Together Same genes, Same environment v. Identical Twins Reared Apart Same genes, Different environment Greater difference between these two groups indicates greater role of the environment (“nurture”). Twin Studies Similarity of IQ Test Scores in Twins Correlation 0.9 0.8 0.7 0.6 0.5 Identical twins reared Identical twins reared together apart Criticisms: 1) Adoption agencies try to place twins in similar families so the variation in environment may be small, and 2) There is a very limited sample. Adoption Studies Is child more like adoptive parents… …or biological parents? Adoptive Parents - Nurture Biological Parents - Nature Adoption Studies Similarity of Temperament Between Adopted Children and their Parents 0.5 Correlation Coefficient Correlation Coefficient Similarity of Values Between Adopted Children and their Parents 0.4 0.3 0.2 0.1 0 Biological parents Adoptive parents 0.6 0.5 0.4 0.3 0.2 0.1 0 Biological parents Adoptive parents • Note: Two related siblings that grow up in the same family are strikingly different in personality (as I’m sure many of you can attest to). Heritability Your turn Analyze the behavior genetics research data to determine the role of nature and nurture in various traits.