Psychology 2220A/B Chapter Notes - Chapter 2: Genetic Recombination, Mendelian Inheritance, Thumb

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We all tend to think about things the ways that have been ingrained in us by our
Zeitgeist, the general intellectual climate of our culture
You are the intellectual product of a Zeitgeist that promises ways of thinking about the
biological bases of behavior that are inconsistent with the facts
We tend to ignore the subtleties, the inconsistencies, and complexities of our
existence and to think in terms of simple mutually exclusive dichotomies: right-wrong,
good-bad, attractive-unattractive, and so on
The allure of this way of thinking is its simplicity
Is it physiological, or is it psychological
Rene Descartes argued that the universe is composed of two elements:
1. Physical matter, which behaves according to the laws of nature and is thus a
suitable object of scientific investigation
2. The human mind which lacks physical substance, controls human behavior,
obeys no natural laws, and is thus the appropriate purview of the Church
Cartesian dualism, as Descartes philosophy became known, was sanctioned by he
Roman Church, and so the idea that the human brain and the mind are separate
entities became even more widely accepted
Is it inherited, or is it learned?
Scholars have debated whether humans and other animals inherit their behavior
capacities or acquire them through learning, referred to as the nature-nurture issue
At the same time that experimental psychology was taking root in North America,
ethology was becoming the dominant approach to the study of behavior in Europe
European ethology focused on the study of instinctive behaviors, and it
emphasized the role of nature, or inherited factors, in behavioral development
Because instinctive behaviors do not seem to be learned, the early ethologists
assumed that they are entirely inherited
Problems with thinking about the biology of behavior in terms of traditional
The physiological debate and the nature-or-nurture debate are based on incorrect
ways of thinking about the biology of behavior
Physiological-or-Psychological Thinking Runs into Difficulty
There are two lines of evidence against physiological-or-psychological thinking
The first line is composed of the many demonstrations that even the most
complex psychological changes can be produced by damage to, or stimulation
of, parts of the brain
The second line of evidence is composed of demonstrations that some
nonhuman species, particularly primate species, possess abilities that were
once assumed to be purely psychological ad thus purely human
Asomatogonsia, a deficiency in the awareness of parts of one’s own body
Asomatognosia typically involves the left side of the body and usually results
from damage to the right parietal lobe
Chapter 2: Evolution, Genetics, and Experience
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Although their brains are less complex than the brains of humans, some
species are capable of levels of psychological complexity that were once
believed to imply the existence of a human mind
Nature-or-Nurture Thinking Runs into Difficulty
Factors other than genetics and learning were shown to influence behavioral
development; factors such as the fetal environment, nutrition, stress, and
sensory stimulation also proved to be influential
Next, it was argued convincingly that behavior always develops under the
combined control of both nature and nurture not under the control of one or the
Like earlier versions of the nature-or-nurture question, the how-much-of-it-is-
genetic-and-how-much-of-it-is-the-result-of-experience version is fundamentally
The problem is that it is based on the premise that genetic factors and
experiential factors combine in an additive fashion - that a behavioral capacity,
such as intelligence, is created through the combination or mixture of so many
parts of genetics and so many parts of experience, rather than through the
interaction of genetics and experience
It is nonsensical to try to understand interactions between two factors by asking
how much each factor contributes
It is sufficient for you to appreciate three general points:
1. Neurons become active long before they are fully developed
2. The subsequent course of their development depends greatly on their
activity, much of what is triggered by external experiences
3. Experience continuously modifies genetic expression
A Model of the Biology of Behavior
The biology of behavior that has been adopted by many biospsychologists
Like other powerful ideas, it is simple and logical
This model boils down to the single premise that all behavior is the product of
interactions among three factors
1. The organism’s genetic endowment, which is a product of its evolution
2. Its experience
3. Its perception of the current situation
Darwin was not the first to suggest that species evolve from preexisting species, but
he was the first to amass a large body of supporting evidence and the first to suggest
how evolution occurs
Darwin presented three kinds of evidence to support his assertion that species evolve:
1. He documented the evolution of fossil records through progressively more recent
geological layers
2. He described striking structural similarities among living species, which
suggested that they had evolved from common ancestors
3. He pointed to the major changes that had been brought about in domestic plants
and animals by programs of selective breeding
Darwin argued that evolution occurs through natural selection
Chapter 2: Evolution, Genetics, and Experience
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He pointed out that the members of each species vary greatly in their structure,
physiology, and behavior, and that the heritable traits that are associated with high
rates of survival and reproduction are the most likely ones to be passed on to future
Fitness, in the Darwinian sense, is the ability of an organism to survive and contribute
its genes to the next generation
True, evolution is a theory, but that does not mean that it is a vague, unreliable
speculation: A scientific theory is an explanation that provides the best current account
of some phenomenon based on the available evidence
Evolution and Behavior
Some behaviors play an obvious role in evolution
Other behaviors play a role that is less obvious but no less important
Two examples are social dominance and courtship display
Social Dominance
The males of many species establish a stable hierarchy of social dominance
through combative encounters with other males
Once a hierarchy is established, hostilities diminish because the low-ranking
males learn to avoid or quickly submit to the dominant males
Social dominance an important factor in evolution. One reason is that in some
species dominant males copulate more than non-dominant males and thus are
more effective in passing on their characteristics to future generations
Another reason why social dominance is an important factor in evolution is that
in some species dominant females are more likely to produce more, and more
healthy, offspring
Courtship Display
An intricate series of courtship displays precedes copulation in many species
But copulation is unlikely to occur if one of the pair fails to react appropriately to
the signs of the other
Courtship displays are thought to promote the evolution of new species
A species is a group of organisms that is reproductively isolated form other
organisms; that is, the members of a species can produce fertile offspring only
by mating with members of the same species
A new species begins to branch off form an existing species is when some
barrier discourages breeding between subpopulation of the existing species
and the remainder of the species
Once such a reproductive barrier forms, the subpopulation evolves
independently of the remainder of the species until cross-fertilization becomes
The reproductive barrier may be geographical or behavioral
Conspecies (members of the same species): only the suitable exchange of
displays between a courting couple will lead to reproduction
Course of Human Evolution
Evolution of Vertebrates
Complex multicellular water-dwelling organisms first appeared on earth about
600 million years ago
About 150 million years laters later, the first chordates evolved
Chapter 2: Evolution, Genetics, and Experience
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