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Behavioral Neuroscience



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  • Prepared by Krista D. Forrest, Ph.D.
    These slides © 2002 Prentice Hall Psychology Publishing.


  • 1. ©1999 Prentice Hall Evolution, Genes, and Behavior Chapter 3
  • 2. ©1999 Prentice Hall Evolution, Genes and Behavior  Unlocking the secrets of genes  The genetics of similarity  Our human heritage: language  Our human heritage: courtship and mating  The genetics of difference  Our human diversity: the case of intelligence
  • 3. ©1999 Prentice Hall Unlocking the Secrets of Genes  Genes and how they operate  Genes  Chromosomes  DNA  Genome  Studying genetic material  Linkage studies  Genetic markers  The link between genetics and behavior
  • 4. ©1999 Prentice Hall Genes and How They Operate  Genes  functional units of heredity which are composed of DNA and specify the structure of proteins.  Chromosomes  rod-shaped structures within cells that carry genes.  DNA (dioxyribonucleic acid)  transfers genetic characteristics by way of coded instructions for the structure of proteins.
  • 5. ©1999 Prentice Hall Studying Genetic Material  Linkage studies  Because genes lying close together on a chromosome may be inherited together across generations, researchers can look for genetic markers in families.  Genetic markers  A segment of DNA that varies among individuals, has a known location on a chromosome, and can function as a genetic landmark for a gene.
  • 6. ©1999 Prentice Hall The Link Between Genes and Behavior  Even when researchers locate a gene on a chromosome, they do not automatically know its role in physical or psychological functioning.  Most human traits are influenced by more than one gene pair.  Examples include height and eye color.
  • 7. ©1999 Prentice Hall The Genetics of Similarity  Evolution  Natural selection  Evolutionary biologists and psychologists  Innate human characteristics
  • 8. ©1999 Prentice Hall Evolution  A change in gene frequencies within a population over many generations;  A mechanism by which genetically influenced characteristics of a population may change.  Changes may occur due to mutations or errors occurring during copying of original DNA sequence.  Changes may occur due to natural selection.
  • 9. ©1999 Prentice Hall Natural Selection  The evolutionary process in which individuals with genetically influences traits that are adaptive in a particular environment:  tend to survive; and  to reproduce in greater numbers.  As a result, their traits become more common in the population.
  • 10. ©1999 Prentice Hall Evolutionary biologists and psychologists  Evolutionary biologists start with an observation about a characteristic and try to account for it in evolutionary terms.  Plumage differences in male and female peacocks  Evolutionary psychologists start by asking what sorts of challenges human beings might have faced and then draw inferences about which behavioral tendencies might have been selected to overcome these challenges.  Avoiding poisonous food and an innate dislike for bitter tastes.
  • 11. ©1999 Prentice Hall Innate Human Characteristics  Infant reflexes  An attraction to novelty  A desire to explore and manipulate objects  An impulse to play and fool around  Basic arithmetic skills
  • 12. ©1999 Prentice Hall The Nature of Language  Language  A system that combines meaningless elements such as sounds or gestures to form structured utterances that convey meaning.
  • 13. ©1999 Prentice Hall The Innate Capacity for Language  Language too complex to be learned bit by bit (Chomsky, 1957, 1980). For example, sentences can have surface and deep structures.  Surface structure  the way a sentence is spoken  Deep structure  how a sentence is to be understood  To transform surface sentence structures into deep ones, children must apply rules of grammar (syntax).
  • 14. ©1999 Prentice Hall Examples of Surface and Deep Structures
  • 15. ©1999 Prentice Hall The Language Acquisition Device  Chomsky suggests that since we don’t teach syntax to toddlers, human brains must contain a language acquisition device.  An innate module that allows young children to develop language if they are exposed to an adequate sampling of conversation.  Therefore, children are born with universal grammar or a sensitivity to the core features common to all languages.  Examples include nouns and verbs, subjects and objects, and negatives.
  • 16. ©1999 Prentice Hall Evidence Supporting the LAD  Children in different cultures go through similar stages of linguistic development.  Children combine words in a way that adults never would.  Adults do not consistently correct their children’s syntax, yet children learn to speak or sign correctly anyway.  Children not exposed to adult language may invent a language of their own  Infants as young as 7 months can derive simple linguistic rules from a string of sounds.
  • 17. ©1999 Prentice Hall Evidence for Learning and Language  The design of computerized neural networks to “learn” aspects of language such as regular and irregular verbs.  Children learn the probability that any given word or syllable will follow another.  Although there are commonalities in language acquisition, there are also many differences.  Parents respond to children’s sentence errors by restating or elaborating on the phrase.  Children imitate these adult recasts and expansions.
  • 18. ©1999 Prentice Hall Our Human Heritage: Courtship and Mating  Sociobiology  Interdisciplinary field that emphasizes evolutionary explanations of social behavior in animals, including humans.  We behave in ways that maximizes our chances of passing on our genes, and to help our close biological relatives, with whom we share genes, to do the same.
  • 19. ©1999 Prentice Hall Gender, Evolution and Sexual Strategies  Because of different kinds of survival and mating problems, the sexes have evolved differently in the areas of aggressiveness, physical dominance, and sexual strategies.  Males compete with other males for access to females, and try to inseminate as many females as possible.  Females conceive and carry only a limited number of pregnancies so they choose fewer more dominant males with good resources and high status.
  • 20. ©1999 Prentice Hall Males  Want sex more often.  Are fickle and promiscuous.  Drawn to sexual novelty and even rape  Are undiscriminating in partner choice.  Concerned with competition and dominance. Females  Want sex less often.  Are devoted and faithful.  Drawn to stability and security.  Are cautious and choosy in partners.  Less concerned with competition and dominance. Gender Differences in Sexual Strategies
  • 21. ©1999 Prentice Hall Evolutionary Psychologists and the Question of Gender Differences  While sociobiologists study nonhuman species’ behaviors and make analogies to human behaviors, evolutionary psychologists consider such analogies simplistic and misleading.  Focus more on commonalities of human mating and dating around the world.
  • 22. ©1999 Prentice Hall Culture and the “Genetic Leash”  Criticisms of sociobiological and evolutionary explanations for sexual behavior include:  Evolutionary explanations of infidelity and monogamy are based on stereotypes.  Actual behavior of humans and other animals fails to conform to images of promiscuous males and coy females.  Human sexual behavior is too varied to be explained solely from an evolutionary perspective.  Historically, available mates for selection were much fewer than they are today.
  • 23. ©1999 Prentice Hall The Genetics of Difference  The meaning of heritability.  Facts about heritability.  Computing heritability.  The study of adopted children.  The study of monozygotic and dizygotic twins.  The study of twins separated at birth.
  • 24. ©1999 Prentice Hall The Meaning of Heritability  A statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group.  Expressed as proportion (.60 or 60/100).  Maximum value is 1.0.  Some variables such as height are highly heritable, other variables such as musical ability are moderately heritable.
  • 25. ©1999 Prentice Hall Facts About Heritability  An estimate of heritability applies only to a particular group living in a particular environment.  Heritability estimates do not apply to individuals, only to variations within a group.  Even highly heritable traits can be modified by the environment.
  • 26. ©1999 Prentice Hall Computing Heritability  Studying adopted children allows researchers to compare correlations between the traits of adopted children and those of their biological and adoptive relatives.  These results are used to compute a estimate of heritability.
  • 27. ©1999 Prentice Hall Computing Heritability  Behavioral geneticists can estimate the heritability of a trait by comparing identical or monozygotic twins to fraternal or dizygotic twins.  If identical twins are more alike than fraternal twins, then the increased similarity must be due to genetic influences.
  • 28. ©1999 Prentice Hall Computing Heritability  Investigators have also studied identical twins who were separated early in life and reared apart.  Any similarities in traits between them should be primarily genetic and should permit a direct estimate of heritability.
  • 29. ©1999 Prentice Hall Our Human Diversity: The Case of Intelligence.  Genes and individual differences.  The question of group differences.  The environment and intelligence.
  • 30. ©1999 Prentice Hall Intelligence: Genes and Individual Differences  Intelligence Quotient (IQ)  A measure of intelligences originally computed by dividing a person’s mental age by his or her chronological age and multiplying the result by 100.  It is now derived from norms provided for standard intelligence tests.  The kind of intelligence that produces high IQ scores is highly heritable.  .50 for children and adolescents  .60 -.80 for adults.
  • 31. ©1999 Prentice Hall Twins and Intelligence  Intelligence scores of identical twins are always more highly correlated than those of fraternal twins.
  • 32. ©1999 Prentice Hall Adopted Children and Intelligence  The scores of adopted children are highly correlated with their biological parents.
  • 33. ©1999 Prentice Hall The Question of Group Differences  Genetics are used to explain differences between groups.  Often these differences are used to justify differential treatment for these groups.  Example: Differences between average IQ scores for African Americans and Caucasian Americans  Genetic explanations have a flaw.  They use heritability estimates based on white samples to estimate the role of heredity in group differences.
  • 34. ©1999 Prentice Hall The Question of Group Differences  The handful of studies that have overcome past methodological problems fail to reveal any genetic differences between blacks and whites on IQ.  Examples:  Children fathered by black and white American soldiers in Germany after WWII and reared in similar German communities did not differ significantly in IQ.  Black and White infants perform equally well on tests for novelty.
  • 35. ©1999 Prentice Hall The Environment and Intelligence.  Experiences that hinder intellectual performance.  Poor prenatal care.  Malnutrition.  Exposure to toxins.  Stressful family circumstances.  Experiences that help intellectual performance.  Good health care and nutrition  Mental enrichment in home and child care or school.