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 34/30 homework 4

World

Grades: Ugh

World

Grades:

A = 86+

B = 75-86

C = 60-75

D = 50-60

Nature, Nurture, and your Brain

Children of alcoholic parents are likely to become alcoholics…

Nature or Nurture?

What determines human sexuality?

Twin Studies:

Chance of homosexual male having homosexual brother: Bailey and Pillard (1991)52% (29/56) of identical twins22% (12/54) of fraternal twins11% (6/57) of adoptive brothers

http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=306995

Chance of homosexual male having homosexual brother: Bailey and Pillard (1991)52% (29/56) of identical twins22% (12/54) of fraternal twins11% (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

CB 15.9X/Y chromosomes in humans

Sex-linked traits: Genes on the X chromosome

50% of males affected, 0 % females affected

Homosexual men are more likely to have gay maternal uncle

50% of males affected, 0 % females affected

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/dispomim.cgi?id=306995

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

Evolutionary success = reproductive success

Evolutionary success = reproductive success

How can a gene exist that inhibits reproduction… Homosexuality.

Genetics and Bisexuality V. Savolainen and L. Lehmann (11 Jan. 2007) Nature 445: 158

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

•Overdominance

•Sexually Antagonistic Selection

•Kin Altruism

H or S

H or SHH

HS SS

HS

possible offspring

Hb75% Normal25% Sickle-cell

Malaria75% Resistant25% Susceptible

Mom

Dad

Sickle-Cell Anemia:an example of Overdominance

S=sickle-cellH=normal

H or S

H or SHH

HS SS

HS

possible offspring

Hb75% Normal25% Sickle-cell

Malaria75% Resistant25% Susceptible

Mom

Dad

An example of Overdominance:homozygous individuals have decreased reproduction, but heterozygous individuals have increased reproduction.

S=sickle-cellH=normal

Overdominance in homosexuality:

The gay genes are passed on by heterozygous individuals who can have a reproduction advantage over individuals without these genes.

Sexually Antagonistic Selection:

Genes may have an advantage in one sex and a disadvantage in the other.

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

Sexually Antagonistic Selection:

Genes for male homosexuality may be passed advantageous in women, and visa versa.

Kin Altruism:

Homosexual family members may increase reproductive success of the other family members.

Kin Altruism

Kin Altruism:

Homosexual family members may increase reproductive success of the other family members.

How can genes for homosexuality, that inhibit reproduction, be successfully inherited?

•Overdominance

•Sexually Antagonistic Selection

•Kin Altruism

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.

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

Environmental effects on homosexualityBirth order: Each elder brother increases probability of homosexuality by 1/3.

Birth weight:Boys born as third sons have lower birth weight.

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

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.

Environmental effects on homosexualityBirth 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.

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

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 34/30 homework 4