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Chapter 2

PSYC 3100 Chapter Notes - Chapter 2: Group Selection, Prosopagnosia, Pleistocene

4 pages78 viewsFall 2012

Course Code
PSYC 3100
Hank Davis

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Chapter 2
The Mechanism of Natural Selection
- Darwin‟s ideas are important to psychology because theory of evolution by natural selection is not just a theory about the past,
but the theory details a process that continually shapes organisms
- Theory argues that all living things are sculpted not by a conscious designer like a human engineer but by the inanimate force of
natural selection
- Proposed process, a mechanism, that could cause evolution natural selection
Darwin‟s Argument
1. Natural populations (giraffes, daisies or, people) could grow exponentially Darwin selected more leisurely reproducer he could
think of, elephants. Assumed that female elephant would begin reproducing by age 30 and would produce 1 offspring/ 10 years,
up to total 6 offspring, then die of old age. Calculated that after 500 years a female would have 15 million living descendants, and
so on. This is exponential growth!
2. Despite this potential for exponential growth, natural populations normally are relatively stable Some elephants do not
produce 6 offspring over their lifetime
3. Many individuals do not leave as many offspring as they might Failure often due to limited resources. Every time elephant A
reproduces, offsprings use food, water and other resources that would otherwise be available for offspring of elephant B.
Populations soon grow to point where resources are inadequate to support more reproduction
4. Those best suited to prevailing environment leave the most offspring Some individuals better than others at finding food,
avoiding predators, fending off parasites, or coping with changes in climate. Better-suited individuals tend to leave more
offspring natural selection
5. Because of heredity, offspring are like their partners Advantages that allowed certain individuals to reproduce in spite of local
environmental challenges will be passed on to next generation. Disadvantages that caused some individuals to fail will not be
passed on. Results of natural selection in on generation form starting point for the next
6. Over many generations, natural selection builds individuals that are well adapted to their environment Traits that make species
well suited become more common in population over time
- “Survival of the fittest” not coined by Darwin, but by his peer, Herbert Spencer not an accurate summary of natural selection;
requires 2 important modifications
o First Reproduction, not mere survival, is what makes a difference in evolution
o Second “fittest” must not mean “those that reproduce”, but must refer to the fit between organism and the
environment; the fittest are the ones best able to cope with local environmental challenges. Unless a trait is reproduced,
it will eventually be lost, what is fit depends on environment because each environment poses a unique set of challenges
Evidence in Favor of Evolution
1. The existence and pattern of the fossil record Shows multitude of plausible ancestor-descendant relationships
2. Homology Fact that the same structural elements are found in very different kinds of creatures, often the function of these
elements is the same in different organisms, but sometimes their function is different
3. The universality of genetic code The genetic code of all living things is structurally the same; genes are made out of the same
elements, arranged according to the same rules
4. The analogy with animal breeding Darwin noted how many different breeds of dogs, sheep, and other domesticated species had
been created simply by selective breeding E.g. a farmer wants denser wool on his sheep, so he breeds the sheep with the
densest wool over many generations
5. Direct observation
A Mistaken View of Evolution: The Great Chain of Being
- Great Chain of being idea that life forms can be ordered in a ladder of complexity and sophistication
- Humans stand between animals and angels in a sequence that rises from inanimate objects to Gods
- God Angels Humans Apes Cats Clams Plants Rocks
- Beings share certain similarities with their nearest neighbours and that beings higher on the scale are considered to have „higher‟
- Mistaken for 2 reasons
o First - Implies evolution proceeds in a linear fashion, with „higher‟ creatures directly related to „lower‟ animals
o Second Implies progress „higher‟ creatures are better and more sophisticated than those below
Natural Selection Crafts Adaptations
- Designs for reproduction are transmitted to offspring; other kinds of designs are not and therefore disappear Called adaptations
o Preserved by natural selection because they aid reproduction in some way
- Naturally occurring variations among individuals are constantly being tested against the environment
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