Chapter 2: Evolution, Genetics, and Experience
2.1 Thinking about the Biology of Behaviour: From Dichotomies to Interactions
•Zeitgeist: the general intellectual climate of our culture, which influences which personal attitudes,
opinions, behaviours and thinking patterns.
•We often fall into the pattern of classifying things according to dichotomies - right/wrong,
good/bad, appealing/unappealing etc... because it is a simple, accessible and fast method for making
•Two questions have been asked based on this limited mode of thinking
oIs the problem psychological OR physiological?
oIs the trait learned OR inherited?
•Is it physiological or psychological?
oThe idea that human processes are either physiological or psychological takes its history from
the time directly proceeding the Dark Ages.
oThe truth at that time was what the church decreed to be the truth.
oDuring the Renaissance, emphasis was placed on art, culture, trade and education. Some
scholars resisted the notion of blindly trusting the Church and began to study the world through
observation, and modern science was born.
oCartesian Dualism: Descartes advocated a dual view which gave a portion of the 'world' to
scientific study and a portion of the 'world' to the church. Descartes argued that the Universe is
made up of both physical and non-physical components, and that to study the differing
components of the world, one had to employ differing methods and views. Science, he claimed,
was an appropriate form of study for the physical components of the world such as the laws of
nature, the human body and physical matter and the Church was an appropriate avenue for
studying the non physical aspects of the Universe, such as the spirit, behaviour and and one's
sense of self. The church supported Descartes in this view, and thus it became widely accepted.
oSome scholars today believe that all behaviour has a physiological basis, while others believe
that there is a component of behaviour that transcends the physical.
•Are human processes inherited or learned?
oNature-Nurture Issue: The debate amongst psychologists centering around whether behaviour
is learned through experience or inherited through genes.
oMost early North-American scientists were firmly of the belief that experience was the most
important determinant of human learning, not genetics.
oEthology: The study of animal behaviour in the wild.
oDuring the time that Americans were studying learning, Europeans had become more involved
in Ethology, and focused on instinctive behaviours.
oInstinctive Behaviour: Pattern of behaviour that is displayed amongst all members of the
species, even when there appears to have been no opportunity for the behaviour to have been
oThey assumed that genetic and heritability factors were the primary determinants of behaviour.
oNeither the early behaviouralists nor the early ethologists were completely correct, but both had
made key insights into behaviour.
•Problems with Thinking about the Biology of Behaviour in Terms of Traditional Dichotomies
•There are two lines of evidence against thinking about the brain-behaviour relationship as a dualist
•Many studies have shown that damage to or stimulation of the brain can radically alter a person's
•Nonhuman species once thought to be incapable of psychological processes have been
demonstrated to possess traits such as self-awareness.
•Asomatognosia: A deficiency in the awareness of parts of one's own body. Asomatognosia
typically affects the left side of the body and is caused by damage in the right parietal lobe.
•Sufferers of asomatognosia demonstrate the connection between the brain and behaviour by
demonstrating that damage to the right parietal lobe (Right sensory cortex, I'm assuming) changes
an individual's self-awareness and perception. If psychological processes did not involve the brain,
then damage to the brain would not affect them.
•Chimpanzees were proven to be self-aware through the use of mirrors. Chimpanzees were allowed
time to habituate themselves to the mirror, then a red mark was painted on their face while they
were asleep (Anesthetized). Upon waking, the chimpanzees inspected the new mark, touched it
while looking in the mirror and overall increased time looking in the mirror by a magnitude of 3.
•Previously, self-awareness was believed to be too complex for the brain to handle, but animals with
simpler brains than ours are able to demonstrate self-awareness as we do. If these animals are self-
aware, the brain may be more responsible for that and other psychological processes previously
thought to be metaphysical and uniquely human.
Nature-Nurture Thinking runs into Difficulty
•Eventually scientists argued convincingly that behaviour is the product of both nature and nurture
together, not one or the other.
•The thinking then shifted to be focused on how much influence nature has and how much influence
•This thinking is flawed because it is the interaction between genetics and experience that produces
behaviour, they are not summed in an additive way to result in a fixed behavioural response.
•Three points should be appreciated about the biology of learning
1. Neurons become active long before they are fully developed
2. The subsequent course of their development (ie. whether or not they survive, how many
branches they form) depends primarily on their activity
3. Experience continually modifies genetic expression.
A Model of the Biology of Behaviour
All behaviour is the product of the interaction between 3 things:
1. The organism's genetic endowment
2. Previous experience
3. The organism's perception of the environment
2.2 Human Evolution
•The theory of evolution is the single most influential theory in biology, proposed by Charles
Darwin in 1859 in his publication On the Origin of Species
•Evolve/Evolution: Species undergo gradual and orderly change over a long period of time,
eventually becoming a new species.
•4 types of evidence were presented by Darwin that evolution is real
1. Documentation of fossils through progressively more recent geological layers
2. Striking similarities between living species (ie. similarity between human hand, cat's paw and
bird's wing), suggesting they shared common ancesters
3. Major changes can be brought about through selective breeding of plants and animals indoors
4. Rapid evolution of animals observed, such as the finchs observed by Darwin after a season of
drought on the Galapagos Island.
•Natural Selection: The method proposed by Darwin through which evolution occurs. This theory
states that traits and behaviours that carry with them a high success rate of mating and survival will
be more likely to be passed on to the next generation. Natural selection, when applied to
generations at a time lead to highly successful methods of reproduction and survival for specific
•Fitness: A Darwinian term denoting an organism's ability to survive and contribute its genetic
material to the next generation.
•The theory of evolution was initially resisted, but as evidence and time continued to increase, more
support was garnered. Today, most biologists feel that the evidence supporting the theory of
evolution is so substantial that it is widely regarded as fact.
Evolution and Behaviour
•Some behaviours play an obvious role in passing on genes such as being able to find food, avoid
predation and defend one's young.
•Some behaviors play a subtle, but still important, role in passing on genes such as social dominance
and courtship displays.
•Males of many species establish a stable hierarchy of social dominance
•Often the hierarchy is determined through physical challenges. Sometimes the challenge involves
violence and harm, other times it involves threatening and posturing until one male backs down.
•The dominant male usually wins competitions against all other males in the group.
•Once a hierarchy is established, violence quickly subsides because lower ranking males quickly
learn to avoid or submit to higher ranking males.
•Low ranking males tend to fight less and lower rankings of the hierarchy are typically only vaguely
•Social dominance is important for many reasons
oIn many species, dominant males copulate more than non-dominant males, thus maximizing the
chance their genes will be passed on.
oIn species with female hierarchies, high ranking females tend to produce stronger and healthier
offspring and in higher numbers than lower ranking females
•Intricate displays of courtship precede copulation in many species.
•Often it is the male who approaches the female and signals his desire to copulate. The female then
responds and the signals escalate back and forth until copulation ensues.
•Copulation is unlikely to occur if either partner fails to respond with the appropriate signals.
•Courtship displays can effect the course of evolution.
oA new species begins to branch off from the parent species when a reproductive barrier is
introduced that discourages a subset of the population from mating with the rest. The barrier
could be physical (Such as birds flocking to an island) or behavioral (Such as developing
unique courtship rituals that are performed only by a subset of the group)
oThe subpopulation evolves independently from that point until reproduction with member of its
former species becomes inviable.
•Conspecifics: Members of the same species.