1. emester Today: Nature, Nurture, and the Brain Next Week: Digestion and Nutrition Week of 4/23: Plants are Cool 5/2 Exam 3 4/27 bonus 3 4/30 homework 4

2. World Grades: Ugh

3. World Grades: A = 86+ B = 75-86 C = 60-75 D = 50-60

4. Nature, Nurture, and your Brain

5. Children of alcoholic parents are likely to become alcoholics… Nature or Nurture?

6. What determines human sexuality?

7. Twin Studies: Chance of homosexual male having homosexual brother: Bailey and Pillard (1991) 52% (29/56) of identical twins 22% (12/54) of fraternal twins 11% (6/57) of adoptive brothers http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=306995

8. Chance of homosexual male having homosexual brother: Bailey and Pillard (1991) 52% (29/56) of identical twins 22% (12/54) of fraternal twins 11% (6/57) of adoptive brothers Correlation of homosexual brothers but not homosexual brother and sister Correlation of homosexual sisters but not homosexual sister and brother http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=306995

9. CB 15.9 X/Y chromosomes in humans

10. Sex-linked traits: Genes on the X chromosome 50% of males affected, 0 % females affected

11. Homosexual men are more likely to have gay maternal uncle 50% of males affected, 0 % females affected

12. Cause or Effect? Brain differences? LeVay (1991) interstitial nucleus of the anterior hypothalamus 3 (INAH-3) 2X larger in the heterosexual men compared to women 2X larger in the heterosexual men compared to homosexual men http://www.ncbi.nlm.nih.gov/entrez/dispo mim.cgi?id=306995

13. There is no gay gene. There are thousands of genes and billions of interconnected neurons. There are likely many genes affecting sexuality.

14. Evolutionary success = reproductive success

15. How can a gene exist that inhibits reproduction… Homosexuality. Genetics and Bisexuality V. Savolainen and L. Lehmann (11 Jan. 2007) Nature 445: 158

16. Evolutionary success = reproductive success How can a gene exist that inhibits reproduction… Homosexuality. Three hypotheses… Your #1 most voted for: Genetics and Bisexuality V. Savolainen and L. Lehmann (11 Jan. 2007) Nature 445: 158

17. Overdominance Sexually Antagonistic Selection Kin Altruism

18. H or S HH HSSS HS possible offspring Hb 75% Normal 25% Sickle-cell Malaria 75% Resistant 25% Susceptible Mom Dad Sickle-Cell Anemia: an example of Overdominance S=sickle-cell H=normal

19. H or S HH HSSS HS possible offspring Hb 75% Normal 25% Sickle-cell Malaria 75% Resistant 25% Susceptible Mom Dad An example of Overdominance: homozygous individuals have decreased reproduction, but heterozygous individuals have increased reproduction. S=sickle-cell H=normal

20. Overdominance in homosexuality: The gay genes are passed on by heterozygous individuals who can have a reproduction advantage over individuals without these genes.

21. Sexually Antagonistic Selection: Genes may have an advantage in one sex and a disadvantage in the other.

22. Large baby size is disadvantageous for women, but advantageous for men.

23. Sexually Antagonistic Selection: Genes for male homosexuality may be passed advantageous in women, and visa versa.

24. Kin Altruism: Homosexual family members may increase reproductive success of the other family members.

25. Kin Altruism

26. Kin Altruism: Homosexual family members may increase reproductive success of the other family members.

27. How can genes for homosexuality, that inhibit reproduction, be successfully inherited? Overdominance Sexually Antagonistic Selection Kin Altruism

28. How can genes for homosexuality, that inhibit reproduction, be successfully inherited? Three hypotheses: Overdominance Sexually Antagonistic Selection Kin Altruism Bisexuality would minimize the all or nothing effects of homosexuality.

29. Environmental effects may also play a role in determining sexuality. Birth order: Each elder brother increases probability of homosexuality by 1/3.

30. Environmental effects on homosexuality Birth order: Each elder brother increases probability of homosexuality by 1/3. Birth weight: Boys born as third sons have lower birth weight.

31. Fig 2. BIRTH WEIGHT, SEXUAL ORIENTATION AND THE SEX OF PRECEDING SIBLINGS (2001) RAY BLANCHARD AND LEE ELLIS J. biosoc. Sci. 33, 451–467 Birth Weight, Sexual Orientation and the Sex of Preceding Siblings

32. Fig 2. BIRTH WEIGHT, SEXUAL ORIENTATION AND THE SEX OF PRECEDING SIBLINGS (2001) RAY BLANCHARD AND LEE ELLIS J. biosoc. Sci. 33, 451–467 Homosexual males with older brothers have a lower birth weight.

33. Environmental effects on homosexuality Birth order: Each elder brother increases probability of homosexuality by 1/3. Birth weight: Boys born as third sons have lower birth weight. Mothers may have immune reaction against male proteins.

34. Both nature and nurture determine human sexuality. Is one more of a choice?

35. emester Today: Nature, Nurture, and the Brain Next Week: Digestion and Nutrition Week of 4/23: Plants are Cool 5/2 Exam 3 4/27 bonus 3 4/30 homework 4