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Chapter 3
Evolution, Heredity, and Behaviour
Chapter 1 – Evolution, Heredity and Behaviour
Slide 1
Evolution Theory
Darwin proposed the idea of biological evolution … the notion that populations
of organisms change over time in a manner that ends up making them more suited
to their environment
This has lead scientists in many areas (but especially biology and psychology) to
consider the adaptive significance of the physical and behavioural characteristics
of their subjects
A distinction is often drawn between:
(1) ultimate causes - events and conditions which, over generations,
have shaped the behaviour of our species, versus
(2) proximate causes - immediate environmental variables that effect
behaviour
Steve’s “Its really a woman’s world” example
Chapter 1 – Evolution, Heredity and Behaviour
Slide 2
Brief History of Darwin
Collected many species of animals during his voyage on the “Beagle” and sent
many of the specimens back to England for later study
Was fascinated by how well animals and plants seemed adapted to their environment
Also became interested in artificial selection … a procedure by which certain
animals are mated to produce offspring with desirable characteristics
Wondered if a similar process might also occur in nature … a natural selection
Began collecting data to support his theory of natural selection … but did not
publish his ideas or data for 20 years … until prompted by finding out that
somebody named Wallace had a similar theory
Published his ideas in a book called “Origin of the Species” … a best seller then,
and now
Chapter 1 – Evolution, Heredity and Behaviour
Slide 3
Premises of Evolution
The 4 basic premises of Darwin’s theory of evolution
1) The plant and animal communities of the world are dynamic, constantly
changing the physical and behavioural characteristics
2) Evolution is gradual. Changes arise through slow and steady environmental
changes. Sudden changes challenge a species’ ability to adapt
3) All organisms descended from a single common ancestor. Over time,
different species evolved, each adapted to their own ecological surroundings
4) Natural selection not only causes changes during changing environments,
it also prevents changes during static environmental conditions
Us versus the whales example
Chapter 1 – Evolution, Heredity and Behaviour
Slide 4
Process of Natural Selection
While “survival of the fittest” is part of evolution theory … fit does not mean
physically fit. Rather fitness is defined in terms of reproductive success which
is measured as the number of viable offspring an organism can produce relative
to the organisms that it competes for resources with.
Two processes affect changes to a species
1) Variation - individuals vary in terms of their physical and behavioural
characteristics. This variation is often discussed in terms of differences
in genotypes (an individuals genetic make-up) and phenotypes (an
individuals physical characteristics and behaviour
phenotypes are the result of the interaction between an organisms
genotype and its environment
2) Competition - competition for food and mates is critical for insuring
natural selection. If there were no competition, fitness would not matter
Chapter 1 – Evolution, Heredity and Behaviour
Slide 5
Natural Selection in Human Evolution
Does natural selection apply to humans as well as to other animals?
There is now strong genetic evidence that we have a common with the
gorillas and chimpanzees
Steve, show that time line thing here, and mention “Clan of the Cave Bear”
As a species we are somewhat “out of control”. Our strong evolutionary
success can be linked to two events in our past:
1) Development of Bipedialism - thereby freeing up the hands for all
sorts of mischief (e.g., tool making, weapons, building in general)
2) Encephalization of the Brain - The larger brain allowed more brain
area to be expended on cognitive operations like thinking, reasoning,
and decision making
another important things it allows is planning … the ability to plan
for and predict future events … oh, and language too!
Chapter 1 – Evolution, Heredity and Behaviour
Slide 6
Genetics and Heredity
Darwin’s work lead the way to new fields of research
including genetics, the examination of the structure and
function of genes, including the manner in which genes
are passed between generations
Included in this is the study of how genes affect an
organisms physical and behavioural makeup
Related to this is the issue
of heredity, the sum of the
traits and tendencies inherited
from one’s parents, grandparents,
and so on
Chapter 1 – Evolution, Heredity and Behaviour
Slide 7
Basic Principles of Genetics
“Genes are segments of genetic material called DNA
(deoxyribonucleic acid) - strands of sugar and phosphate
that are connected by nucleotide molecules of adenine,
thymine, guanine, and cytosine”
DNA is in the form of a twisted ladder, with the sugar and
phosphate forming the sides, and all those nucleotide things
forming the rings
The sequence of the nucleotide molecules directs the
protein synthesis that control the biological and physical
development of the body … and behaviour??
> cool book … “The Double Helix”
Chapter 1 – Evolution, Heredity and Behaviour
Slide 8
Heredity, Variability, & Chromosomes
Genes are located on chromosomes, and each chromosome
contains a different sequence of genes
We inherit 23 chromosomes from each of our parents,
giving us 23 pairs. Different pairs control different things,
for example one pair determines gender characteristics
Sexual reproduction involves the union of a sperm and an
ova … each of which are formed through a special form of
cell division called meiosis
The 23 pairs of chromosomes split into two groups with one
member of each pair joining each group … allowing for
223 or 8,388,608 different combos of sperm or ova per
person … allowing 70 trillion possible kids per couple!!
Chapter 1 – Evolution, Heredity and Behaviour
Slide 9
What’s the Big Deal About Sex?
The vast majority of organisms reproduce via a sexual
process of some sort … why sex??
As seen by the previous “couple” number, the need for
two individuals to jointly create one greatly increases the
genetic diversity of the organism … make it more able
to evolve if evolution is necessary
Nasty bug example - yuck!
Chapter 1 – Evolution, Heredity and Behaviour
Slide 10
Genetics and Psychology
Chapter 1 – Evolution, Heredity and Behaviour
Slide 11
Genetics and Psychology
The image to the left is a colorblindness
test - colorblindness is determined primarily
through genetics … can you see the shapes?
OK, now for another example … the taste test!
The moral? Our perception of the world is largely
determined by our genetic make-up. How far do
genetics go in explaining human experience and behaviour?
Chapter 1 – Evolution, Heredity and Behaviour
Slide 12
The Example of Alcoholism
Alcoholism can obviously be a very destructive
“disease” … how much is it due to genetic factors?
Twin Studies Concordance rate for alcoholism is higher for MZ than
for DZ twins (76 vs 61 for males, 36 vs 25 for females)
This is true even when the kids are not raised by their
biological parents
Chapter 1 – Evolution, Heredity and Behaviour
Slide 13
The Challenge of Altruism
As a final look at Evolution Theory, let’s consider the
challenge that is posed by altruistic behaviours
An altruistic behaviour is one in which an organism does
something that puts itself at risk, in order to aid another
Many animals (including humans) perform altruistic
acts - for example, howling wolves warning of predators
Surely these behaviors
defy the notions of
Evolution Theory, right?
Chapter 1 – Evolution, Heredity and Behaviour
Turtle soup chef coming!!
Run for your lives!! Ahh!!
Slide 14
First Reply to the Challenge - Inclusive
Fitness
Hamilton (1964) argued that evolution is not really focused
on the reproductive success of the “individual” but rather
focuses on the reproductive success of the “gene”
Often times, altruistic acts are directed towards close
family members who share many of the same geners
… especially towards children
Thus, although the altruistic act may hurt one individual
carrying a certain gene, in doing so it may serve the “greater
good” of preserving the same genes in related individuals
This notion is termed inclusive fitness
Chapter 1 – Evolution, Heredity and Behaviour
Slide 15
Second Reply - Reciprocal Altruism
But not all altruistic acts are directed at family members,
what of the acts directed at total strangers?
Trivers (1971) claims that Evolution Theory also has an
answer to that … reciprocal altruism
This notion is that an individual considering performing
an altruistic act towards a stranger will do so if the
potential benefits of the acts outweigh the risk
If the benefits do outweigh the costs, then the individual
can increase their reproductive success by performing the
act and does so … a somewhat dark view of altruism eh?
Chapter 1 – Evolution, Heredity and Behaviour
Slide 16
Summary of Chapter 3
There is no doubt that our genes affect the manner in which
be perceive and relate to the world around us
Evolution Theory provides a theoretical framework for
understanding (a) how we as humans have come to be as
we are and (b) why we may act as we do in certain situations
Often, when one proposes a theory of human behaviour,
they include some discussion of their theory in terms of
Evolutionary Adaptiveness … e.g., inhibition of return
Chapter 1 – Evolution, Heredity and Behaviour
Slide 17
Inhibition of Return Example
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Chapter 1 – Evolution, Heredity and Behaviour
Slide 18
Inhibition of Return Example
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Chapter 1 – Evolution, Heredity and Behaviour
Slide 19
Inhibition of Return Example
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Chapter 1 – Evolution, Heredity and Behaviour
Slide 20
Inhibition of Return Example
A
Subjects are faster when the target is in a new area of the
screen, than if it is in the area that was flashed, why?
Chapter 1 – Evolution, Heredity and Behaviour
Slide 21