last updated:

Feb. 10, 2021


[Brain Image]    

PSY 340 Brain and Behavior

Class 03: Genetics and the Evolution of Behavior (OUTLINE)


QUESTION: When we use the word "gene" what do we are we saying? What is a "gene"?

ANSWER: Two different (though related) meanings

(1) An inherited biological unit or factor that determines some physical trait [= Mendelian genetics]


(2)  Inherited molecule(s) or sequences of DNA which give the code(s) or instructions for the production of specific proteins within cells [= Molecular genetics]

Examples of Mendian Traits
Dominant Trait
Recessive Trait

Tongue Rolling
Can Cannot
Ear Lobe
Hangs free
Hand Clasping
Left thumb on top
Right thumb on top
Hitchhiker's thumb
Straight thumb
Bent thumb
Hair Curly
Other traits
 Dimples No Dimples

Freckles No Freckles
   Farsightedness Normal Vision

Normal Vision Nearsightedness

Low sensitivity to Poison Ivy High sensitivity to Poison Ivy

Mendelian Genetics

[Gregor Mendel]   [Watson & Crick    [Animated DNA]

• Gregor Mendel (1822-1884)
the rules of inheritance through genes

Molecular Genetics (DNA)

• chromosomes
• DNA (Deoxyribonucleic Acid).
• James Watson and Francis Crick (discovered shape)

            1956 DNA-RNA-Protein Suggestion

• DNA  ribonucleic acid (RNA)(synthesize) →  protein molecules (see figure "Function of DNA below).

[Human Chromosomes]     Function of

[Gene]Chromosomes & Genes

Human beings have 23 pairs of chromosomes (see above)

Heritable (Simple) Traits

[Trait Transmission: Eye Color]   

Researchers on eye color found these additional genes when they looked not at simple color (brown vs. blue vs. hazel), but at very fine differences in the hue (actual color) and saturation (purity of the color) of thousands of eyes. They then compared these differences with the complete genomes of the individuals.

Genetic Changes (Molecular Genetics)

Heredity & Environment

 • many genes (= polygenetic inheritance) X environmental conditions

Heritability or the Heritability Index (H2): estimate of how much variation or differences in a characteristic across a population are due to differences in heredity. In a different sense, the heritabilty index tells us how much we can reduce our error of predicting whether one identical twin has a trait if the other twin has the trait.

Population Average BP 50% fall within the range of Heritability (H2)
African American
145/87 127/77 to 150/93 0.70
Italian Americans 137/81 120/73 to 148/89 0.40

Research on heritability comes from

Problems in Heritability Research
Environmental Modification
The Evolution of Behavior

Corrections to WRONG IDEAS about evolution

Brain Evolution: importance of cooking & change in gene for glucose transport to brain

[E. O. Wilson]Evolutionary Psychology (aka SOCIOBIOLOGY) founded by Dr. Edward O. Wilson (Harvard U. Biologist)

What are the evolutionary bases of behaviors? E.g., goose bumps, infant grasp reflex

Altruistic Behavior

 • Simple altruism
 • Reciprocal altruism: help others who will also help you
(especially with cultural sanctions against "cheaters")
 • Kin selection: help given to those who share same genetic inheritance
• Group selection
(a controversial theory): cooperative groups > non-cooperative groups