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Chapter 3

PSYA01H3 Chapter Notes - Chapter 3: Parental Investment, Probability Distribution, Phenylalanine

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Steve Joordens

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Chapter 3 Evolution, Heredity and Behaviour
Case study: There was a pilot who transports sick patients to the hospital his name was
Martin Hartwell. The plane crashed and two of the patients died but the pilot and a body
named David (suffered from appendicitis) survived. However the pilot was unable to walk
because he suffered multiple fractures. David helped the pilot survive by gathering food and
such and died after 20 days. 12 days after David’s death the pilot was found and rescued.
Charles Darwin Darwin proposed the idea of biological evolution … the notion
that populations of organisms change over time (physically and behaviourally) in a manner
that ends up making them better adapted 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
(2) proximate causes - immediate environmental variables that effect behaviour
Charles Darwin collected many species (finches and tortoise of Galapagos Islands) of
animals during his voyage on the “Beagle” and sent many of the specimens back to England
for later study he was fascinated by how well animals and plants seemed adapted to their
environment and he also became interested in artificial selection … a procedure by which
certain animals are mated to produce offspring with desirable characteristics (like breeding
certain dogs)
Natural selection
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
While “survival of the fittest” is part of evolution theory … fitness is defined in terms of
reproductive success, which is measured by 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
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