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Course Code
PSYC 280
Ollie Hulme

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Chapter 6 Evolution ETM142011 PSYC 221
First assumed each species created separately
Mid 19th Century:
Research into the fossil record & diversity of living organisms convinced scientists that species evolve.
Natural Selection
Theory proposed by Charles Darwin & Alfred Wallace (1858)
Gradually causes substantial changes in species. They evolve.
Darwin Makes 3 Observations:
1.Individuals of a species vary.
2.Some variation is inherited from parents.
3.Not all individuals manage to reproduce.
And 1 Inference:
Those individuals who vary in ways which suit their environment are those that survive and reproduce,
and thus pass them on to the next generation. Those adaptations are thus naturally selected.
Physiological Adaptation:
Physiology is a product of natural selection.
Adaptations which have promoted survival and reproduction of ancestors.
Psychological Adaptation:
Psychology is a product of natural selection too.
Memory, emotions, decision making, personality, language, perception, consciousness all helped
ancestors survive and reproduce
Mechanisms of Inheritance
Laws of Inheritance:
Mendel showed in pea plants how traits could be inherited down generations.
De Vries showed how new variants could arise by mutation.
oMost mutations are non-adaptive
oSome are adaptive, therefore pass down through generations.
Watson & Crick
Molecular basis of inheritance and variation
DNA, the molecules passed down through reproduction that carry the information for instructions for
building the organism.
Tree of Life:
Species genus family order class phylum kingdom
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Chapter 6 Evolution ETM142011 PSYC 221
Mutation and selection produced the diversity of living organisms.
Sexual Selection
Where the mate selection process influences which traits are selected to pass to the next generation.
Can drive dramatic adaptations that don’t aid survival, but enhance the ability to reproduce.
Example Songbirds:
Females prefer males with larger song repertoire.
Males with larger Higher Vocal Centers = better repertoires.
When females sexually select to reproduce with those with large repertoires, they are selecting for
larger HVC’s.
Brain Size
Size Principle:
Size of a brain region in a species tells you how important that function is for its behavior
Food storing birds need better memories greater proportion of brain (hippocampus) dedicated to
Common Vertebrate Principes:
Develop from hollow neural tube.
Functional localization
All likely due to the fact that we descended from common ancestors.
Absolute size or relative size of brain regions
oE.g., humans have larger cerebral hemispheres and surface area of the cortex than rats, who
have larger olfactory regions.
Human neurons have larger neurons than mammals.
Brain Size vs. Body Size:
Brain weight generally proportional to body weight
Encephalization Factor:
Measures how much bigger your brain is relative to your body
Further off the line larger (or smaller) brain relative to body size larger encephalization factor
Humans have the largest
Larger Regions:
Regions that develop last are generally larger.
Prefrontal cortex is largest in humans, and still develops into adulthood.
Outer layers of cortex develop last and have enlarged most in humans.
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