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Chapter 12

CHAPTER 12.docx


Department
Psychology
Course Code
PSY351H5
Professor
Evo
Chapter
12

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of 3
CHAPTER 12
EVOLUTION OF HUMANS
Evolutionary psychology: attempts to apply the principles of adaptation and selection to human
behavior
Evolutionary Theory
Ideas by others, but put together by Darwin and Wallace;
1) Classification of organisms based on structure by Carolus Linnaeus
2) Charles Lyell and William Smith observed that the earth was far older than was previously
thought through the studies of fossils and geological processes
3) Thomas Malthus observed the food supplies affect populations (survival of the fittest)
Historical Theory of Evolution
Historical theory of evolution can be summed up by three terms; variation, inheritance, and
differential reproduction
All individuals vary, which results in differences in morphology, which can be passed from one
generation to the next, and these individual differences in morphology can result in variations in
success in the environment in terms of survival and reproduction
Darwin suggested that the mechanism underlying these changes was natural selection: requires
that all individuals are unique and that characteristics that give an animal a reproductive
advantage will result in the magnification of these traits in the population
Adaptation: when a trait results in a reproductive advantage and is selected for
For a trait to be an adaptation it must be inherited from one generation to the next
Sexual selection: it is competition among individuals for survival to reproduce that determines
which genes remain in the gene pool and which genes disappear from the face of the planet
Two types of sexual reproduction:
1) Intersexual selection: one sex chooses a mate from among members of the other sex on the
basis of specific traits
2) Intrasexual selection: members of the same sex compete for partners of the opposite sex
The original theory of evolution is referred to as the historical theory of evolution because of
the changes to the theory that have occurred since its inception since when Darwin and Wallace
formulated the theory of natural selection, they did not know why variation occurred, or how
traits were passed down
We now know traits are passed down by genes and that the original source of variation is the
random mutation of these genes
Current theory of evolution is referred to as the Modern Synthetic Theory of Evolution or
modern synthesis
Modern Synthesis
Is based on what is known about genes, DNA, and population biology
Your genotype is invariant during your lifetime, phenotype is the interaction of your genotype
with the environment in which you develop
More than one form of a gene = alleles
Homozygous = both alleles are the same
Heterozygous= two different alleles
Polygenic trait: when multiple genes affect a trait
Mutation occurs when there is a change in genotype due to the error in replication of DNA
Central tenet of the modern synthesis is that certain environments select certain phenotypes
and phenotypes are an expression of the genotype interacting with the environment.
Environments does not produce adaptations; rather, mutations result in characteristics that in a
specific environment are either adaptive, neutral or deleterious for the organism
Although genes occur at the level of the individual, evolutionary change occurs at the level of
populations
- Genetic drift: the tendency for isolated populations to depart from the original genetic
composition of the population
- Gene flow: is the movement of genes through a population that results from mating
Species represent different gene pools, rather than fundamentally unique groups. Species are
judged as such by their genotype, not by their phenotype
Three major differences between the modern synthetic theory and the historical evolution
theory:
a) The modern theory recognizes that traits are the result of genes that are inherited from
one’s parents and interact with the environment
b) The recognition that there are mechanisms other than natural selection that can effect
evolutionary change
c) The recognition that what we call species are only differences in gene pools of a population,
not totally distinct or new organisms that arrived fully formed from somewhere
Evolution of the Nervous System
Researchers examine fossilized skulls to obtain clues regarding the brains of our ancestors
Another way to examine the skull of animals is to make an endocast, or a mold of the inside of
the skull
Other researchers suggest that brain evolution can be studied by comparing brains of humans
with those of other primates
Comparisons of the brainstem with the cortex tend to focus on three major points of difference
among the species
1) Newer species have larger brains
2) The increase in size is observed in newer species is primarily in cortical areas
3) Newer species have an increasingly complex cortex, as defined by the number of layers of
cells and the number of cortical convolutions
EVOLUTION OF BEHAVIOUR
Proximate vs. ultimate Cause
Proximate Cause: addressed by “how” questions of a behavior
- describe the internal mechanisms that underlie a behavior
- Can be characterized as the immediate cause of behavior
Ultimate Cause: addressed by “why” questions of a behavior
- Describe the evolutionary basis behind a behavior including a description of what makes a
given behavior adaptive
Adaptations Are Not Always Adaptive Forever
Ex. Seeking sweet foods (such as fruits) would provide nutrients such as vitamins and would be
preferred by our ancestor, however, today, most sweets come in the form of junk food, with not
much nutritional value, therefore this preference is no longer adaptive
Evolutionary Psychology
Fossil record informs us about more than structural changes during evolution
Provides clues about ancient behavior
The Tabula Rasa
Before Darwin’s publication, there was a commonly held belief that the human brain resembles
a blank stale (tabula rasa) at birth and that all knowledge must be acquired through experience
This position was clearly articulated by John Locke, who claimed that no person’s knowledge can
go beyond his or her experience and that there are no such things as innate ideas
Innate human Characteristic
An adaptation is a system of properties or mechanisms molded by natural selection because it
helped to solve a specific adaptive problem posed by the physical, chemical, developmental,
ecological, demographic, social or informational environment
Adaptations have a number of properties:
1. Recur across generation
2. Appear reliably over the developmental life of the organism
3. Appearance is influenced by genetic specifications
4. Interact with features of the environment that are normally present
5. Help to solve an “adaptive problem” that the organism’s ancestors would have faced
6. Were propagated during a period of selection because they enhance the survival and/or
reproduction of the individual
How Does Evolutionary Psychology Inform Neuropsychology?
Following left hemisphere temporal lobe damage, people often have difficuly discerning the
meaning of spoken words usually the result of damage to Wernicke’s area, a region of the
brain that is specialized for linking sounds with linguistic labels and meanings
Evolutionary psychology can simplify our explorations of the rbain in a number of ways
- Can help us to define which functions we should attempt to localize