Introduction to PsychologySuzy Scherf

Lecture 4: How Do We Act?

Biological Basis of Behavior

Why Learn About Biology?

• Permits us to see human behavior as having a lot in common with that of other animals.

• When the biology/brain is disrupted, so is behavior!

• Considering our biology enables us to see how evolutionary processes have shaped our behavior.

The Mechanism of Heredity

• If a trait is not heritable -

• Genes are -

• Genes code for ________ human traits as well as a ________ set of individual traits

The Mechanism of Heredity

• Genes not diluted when combined -

• Normal adults diploid -

• Genes are particles

The Structure of Genetic Material

• Genes have different versions called ________

• For each gene -

The Structure of Genetic Material

Kinds of alleles:

1. Homozygous -

2. Heterozygous - different versions of alleles

The Structure of Genetic Material

Kinds of Heterozygous alleles:

1. Dominant -

2. Recessive -

The Structure of Genetic Material

Kinds of Heterozygous alleles:

3. Co-Dominant -

The Structure of Genetic Material

• 23 pairs of chromosomes in each cell

• Each chromosome has a definite structure -

• Genes organized as ___________ in nucleus of all cells

Human Chromosomes

Human Chromosomes

De Brazza Monkey Chromosomes

Sexual Reproduction and Genetic Transmission

• Offspring get __% genes from mom and __% from dad

• Why not reproduce asexually and pass on 100% of genes?

The Need for Genetic Variation

Evolution needs to have genetic variation in order to select the genes that contribute to solving the problems presented by the local environment.

Major Sources of Genetic Variation

1. Each mature sex cell has 1 per 8 billion possible assortments of chromosomes.

2. During meiosis crossing over -

Major Sources of Genetic Variation

3. Random Assortment -

4. Mutations -

Genes to Traits

• Genes always working in combination with the environment -

• Genes don’t directly make bones, muscle, or brains

• Genes code and oversee the assembly of specific _______ and _________

Genes and Traits

• Very rarely does a single gene determine a trait, most especially a behavioral trait.

• Most behavioral traits are polygenetic -

Genotype vs. Phenotype

• Genotype -

• Phenotype -

Determinants of Phenotypic Expression

1. Reaction Range -

2. Canalization -

Determinants of Phenotypic Expression

3. Resilient Traits -

4. Fragile Traits -

Genetic Fallacy:

Beware!

How do Genes Affect Behavior and Development?

Genes code for:

1.

2.

3.

4.

1. Genes influence the development of facultative traits -

How do Genes Affect Behavior and Development?

2. Genes influence way the central nervous system works

2. Genes influence way the central nervous system works

How do Genes Affect Behavior and Development?

1. What are our brains for?

2. How do our brains work?

Two Focused Questions on Brains

Does Size Matter?

What’s Special about Our Brain?

Does Shape Matter?

What’s Special about Our Brain?

• Australopithecus afarensis• Ethiopia 3.5 million yrs.

old• 3’8” tall• 1/3 brain size of modern

humans

Lucy’s Skull Neanderthal Skull• Archaic Homo Sapiens• 300,000 years ago• Brain size 1175 cc• Modern human brain size

1400 cc

Evolutionary Scale

Lucy Neanderthal Human

What’s Special about our Brains?

Body wt (kg) Brain wt. (g) Ratio (g/kg)Cow 465 423 0.91Elephant 2547 4603 1.81Gorilla 207 406 1.96Chimp 52.16 440 8.44Human 62 1320 21.29

What’s Special about our Brains?

What’s Special about our Brains?

Passingham (2002)

What’s Special about our Brains?

Semendeferi et al. (2002)

What’s Special about our Brains?

• Brain:body ratio

• Size and organization of more specific cortical areas within frontal cortex -

• Amount of frontal cortex -