Class 17: Some Notes on Heredity and Evolutionary Psychology (Outline)

Heredity & Behavior

Are the sayings true: like father, like son, or, like mother, like daughter? Does craziness run in families? Is biology destiny?

Basic Principles of Genetics

Chromosomes = Long strands of DNA

Genes = segments on a chromosome with instructions for producing proteins

Human beings have 23 pairs of chromosomes

Research Strategies

1. Family studies

2. Twin studies

3. Adoption studies

     Example: Schizophrenic (SCZ) Disorders

concordance rates:

• Random pair in general population ≤ 1% concordance rate
• First cousins = 2% concordance rate
• Siblings = 9% concordance rate
• Identical twins = 40-50% concordance rate

Why is this evidence that SCZ cannot be merely an hereditary disorder, that is, that SCZ is not due solely to genetic influences?

4. Genome Mapping (Genome Wide Association Studies, GWAS)

• Vastly reduced cost of sequencing individual genome (all the genes in a single individual): ca. $1,000 today (vs. $100 million in 2001). This allows studies of many hundreds or thousands of individuals at the same time.
  

• Expectation: finding single or small number of genes associated with mental conditions and behaviors

• Findings: most mental conditions (e.g., SCZ or bipolar disorder) and behavioral traits (e.g., intelligence levels) are the result of multiple small effects of many genes (dozens, hundreds, perhaps thousands) interacting with each other.
  

The Interplay of Heredity & Environment

1. Polygenetic determinism

Single Gene Disorders	Multiple Gene - Polygenetic Disorders
cystic fibrosis alpha- and beta- thalassemias (less hemoglobin than normal) sickle cell anemia (sickle cell disease) Marfan syndrome (connective tissue disorder) fragile X syndrome Huntington's disease hemochromatosis (too much iron stored)	heart disease high blood pressure Alzheimer's disease arthritis diabetes cancer obesity

2. Genetic vulnerability (called a "diathesis" in medicine). Thus, diathesis + high environmental stress = disorder.

3. Epigenetics = study of heritable changes in how genes express themselves that do NOT involve modifications to the DNA sequence.

4. Most traits are the result of the combined effects of heredity and environment (see chart below):

The Evolutionary Basis of Behavior

Is monogamy natural?    Are humans doomed as a species because our minds were fundamentally shaped by the demands of the Stone Age, but we now live in a world of germ warfare, atomic weapons, and the potential to kill the planet?    Are men programmed or destined to be unfaithful to their wives?    Are women less interested in sex than men are?    Is it natural that men mostly look for beautiful women while women mostly look for men who are (potentially) rich or influential?

Charles Darwin's Theory (1859: On the Origin of Species by Means of Natural Selection) Various physical characteristics or traits emerge due to random genetic changes & an be passed down to subsequent generations. He didn't know the actual mechanism of genes (i.e., DNA), but knew there was some physical mechanism involved in how living creatures develop.    Fitness   Natural selection

Modern Refinements = Evolutionary Psychology

• Adaptation
  
• Behaviors As Adaptive Traits

• Non-human animals

• Among humans, such behavior traits almost certainly include the powerful urge to socialize with others, to make friends, the ability to understand the intentions of others, to learn language(s) as children without having to study them, etc. The Garcia Effect we studied last week would be another example: one-shot learning of what is poisonous or harmful helps survival.