Last updated: September 29, 2021
Class 16: Some Notes on Heredity and Evolutionary Psychology

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

Cell to DNA

Human Male KaryotypeChromosomes = strands of DNA (deoxyribonucleic acid) molecules that carry genetic information.

Genes = segments of DNA that serve as the key functional unit in hereditary transmission. Each gene contains the blueprint or template for the production of a protein.

Human beings have 23 pairs of chromosomes: 22 pairs plus for men an X & Y chromosome and for women two X chromosomes.


              Family Relatedness]Research Strategies

1. Family studies: Examine blood relatives to see how much they resemble one another on a trait
2. Twin studies: Monozygotic (identical) twins [share 100% of same genes] vs. dizygotic (fraternal) twins [share ca. 50% of same genes] (see chart on right)
3. Adoption studies: adopted children compared to adoptive parents vs. birth parents

     Example: Schizophrenic (SCZ) Disorders (see chart on right)

Note: A concordance rate means the odds (expressed as a percentage) that, if one member of a population has a factor/disorder/trait, another member will have that factor/disorder/trait

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

                per genome 20174. Genetic Mapping (= Genome Wide Association Studies, GWAS)

The Interplay of Heredity & Environment

1. Traits associated with genes are usually not associated with just a single gene but with a network, group, or set of multiple genes = 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

2. We tend not to inherit a disorder genetically, but a genetic vulnerability to or disposition for disorder (this vulnerabilty is called a "diathesis" in medicine) which must be triggered or induced by experiences within the environment. Thus, diathesis + high environmental stress = disorder. At the end of the semester we will look at some of the environmental triggers associated with SCZ.

3. Epigenetics = study of heritable changes in how genes express themselves that do NOT involve modifications to the DNA sequence. Recent findings show that certain environmental effects such as high stress or various chemicals in the environment can lead to the silencing of genes or reducing how well they can cause things to happen (in biology, often resulting from a process called DNA methylation) without actually eliminating or changing the genes themselves. Some of these changes can be passed on to the next generation. 

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?

Some of these questions may sound like something to be argued on Oprah. But, they are some of the kinds of questions which are often suggested by aspects of the relatively new theory of evolutionary psychology.

[Darwin's On the Origin of Species]

[Charles Darwin]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. These traits can be passed down to subsequent generations. He didn't know the actual mechanism of genes (i.e., chromosomes with DNA), but knew there was some physical mechanism involved in how living creatures develop.
  • Fitness: a characteristic which makes an organism more likely to have reproductive success (that is, have offspring) compared to the average member of a population. BY THE WAY, Darwin did not talk about the "survival of the fittest" but believed in the survival of the "more fit".
  • Natural selection: the process by which hereditary characteristics tend to survive or be passed on (that is, "selected" out or "chosen" by nature) because such characteristics make the organism either
    • More likely to survive to have offspring and pass the characteristic to a new generation, or
    • More likely to attract a mate so that offspring result and the characteristic is passed to a new generation

Modern Refinements = Evolutionary Psychology


Willoughby, E. A., Love, A. C., McGue, M., Iacono, W. G., Quigley, J., & Lee, J. J. (2018, June 24). Free will, determinism, and intuitive judgments about the heritability of behavior. https://doi.org/10.31219/osf.io/ezg2j