Download Biological Bases of Behavior

Introduction to Psychology
Suzy 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.
• Considering our biology enables us to see how
evolutionary processes have shaped our behavior.
• When the biology/brain is disrupted, so is
behavior!
The Mechanism of Heredity
• If a trait is not heritable -
• Genes code for ________ human traits as well
as a ________ set of individual traits
• Genes are -
The Mechanism of Heredity
• Genes are particles
• Genes not diluted when combined -
• Normal adults diploid -
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
• Genes organized as ___________ in nucleus of
all cells
• 23 pairs of chromosomes in each cell
• Each chromosome has a definite structure -
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 -
Beware!
Genetic Fallacy:
How do Genes Affect Behavior and
Development?
Genes code for:
1.
2.
3.
4.
How do Genes Affect Behavior and
Development?
1. Genes influence the development of facultative
traits -
2. Genes influence way the central nervous system
works
How do Genes Affect Behavior and
Development?
2. Genes influence way the central nervous system
works
Two Focused Questions on Brains
1. What are our brains for?
2. How do our brains work?
What’s Special about Our Brain?
Does Size Matter?
What’s Special about Our Brain?
Does Shape Matter?
Lucy’s Skull
• Australopithecus afarensis
• Ethiopia 3.5 million yrs.
old
• 3’8” tall
• 1/3 brain size of modern
humans
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?
What’s Special about our Brains?
Cow
Elephant
Gorilla
Chim p
Human
Body wt (kg) Brain wt. (g) Ratio (g/kg)
465
423
0.91
2547
4603
1.81
207
406
1.96
52.16
440
8.44
62
1320
21.29
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
• Amount of frontal cortex -
• Size and organization of more specific cortical
areas within frontal cortex -