Evolution, Heredity, and Behaviour

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Chapter 3

• Evolution, Heredity, and Behaviour

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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
Steves Its really a womans world example
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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
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Premises of Evolution
The 4 basic premises of Darwins 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
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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
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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!
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Genetics and Heredity
Darwins 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 ones parents,
grandparents, and so on
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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?? gt cool book
The Double Helix
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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!!
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Whats 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!
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Genetics and Psychology
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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?
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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
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The Challenge of Altruism
As a final look at Evolution Theory, lets
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?
Turtle soup chef coming!! Run for your lives!!
Ahh!!
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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
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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?
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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
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Inhibition of Return Example

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Inhibition of Return Example

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Inhibition of Return Example

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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?