Lecture 8, 9, 10 Chapter 3 2/5/2013 11:01:00 AM
Chapter three: Genes, Evolution, and Environment
Where do Differences Come from?
Previously two perspectives:
Emphasized genes and inborn characteristics (nature)
Focused on learning and experience (nurture)
The Genetics of Similarity:
Evolution is a change in gene frequencies within a population over many
Changed may result from:
o Mutations (errors in copying of DNA sequences during division of cells
that produce sperm and eggs.)
o During formation of sperm or eggs small segments of DNA can cross over
to another chromosome pair.
Evolutionary process formulated by Darwin.
Individuals with genetically influences traits that are adaptive in particular
environments ten to survive and reproduce in greater numbers (“survival of the
As a result, traits become more common in the population.
Darwin also proposed that genes were determined by sexual selection.
o A member of one sex chooses a mate from the other sec on the basis of
o Members of the same sex compete for a partner of the other sex.
Darwin to psychology:
So we may have psychological functions that are adaptive.
This was the focus of the “functionalists” in the US in the early 20 century. o Though all psychology served a “function”
Led to the idea of mental modules.
One perspective is that mind reflects mental modules shaped through evolution:
o Mental modules:
A collection of specialized and independent sections of the brain,
developed to handle specific survival problems (e.g. location of
food, finding a mate)
Critics point out that not all traits are adaptive but may be by-products of other
traits (not isolated)… your belly button is a by product trait.
Innate Human Characteristics:
Evolution has shaped human development through innate characteristic such as:
o Infant reflexes
o An interest in novelty
o A desire to explore and manipulate objects
o An impulses to play and fool around
o Basic cognitive skills.
How Nativism was misused:
Many of Darwin views were misused by people to make very racist claims
o People from different parts of the world “evolved” different brains and
o Used it to justify slavery and “modernization” of “primitive” societies
o Intelligence testing grew from this; tests meant to show that there were
Similarly used to make sexist claims.
Then came Watson:
John Watson was no saint
Did have one very good notion
“you can take any child from anywhere and they can learn how to do anything”
flew in the face of the nativists; suggested the opposite… that very little was
inborn and certainly that there were no differences in races or sexes.
Differences observed were due to learning. Behaviourism again:
So behaviourists claimed that psychology was learned, and not genetic.
Aggressiveness, kindness, knowledge, preferences, aptitudes all learned.
But there is a problem
Some traits are definitely inherited (innate), some traits are definitely learned,
some are both
o Language is an example of “both”
So it looks like we need to understand how genes and environment interact with
one another to unlock why people are the way they are.
Unlocking the secrets of genes:
Genes are the basic units o heredity that are composed of DNA and located on
o Rod shaped structures found in the cell nucleus of every cell (23 pairs)
o chromosomal molecule that transfers genetic characteristics by way of
coded instructions for the structure of proteins.
Within genes, four chemical elements of DNA “code” for protein synthesis:
o Adenine (A) Cytosine (C)
o Thymine (T) Guanine (G)
o full set of genes in each cell of an organism (except sperm and egg cells)
Genes and psychology:
The idea is that we inherit personality and intellect through our genes.
People vary from their parents genetically because of
o Mutations (even identical twins are 100% identical)
o Recessive genes.
* Genes, environment and psychology:
So how do we know what psychological traits and abilities are genetic and which
Why might it be important to know if a trait is genetic or learned. o May want to look at environmental factors more than genes; can add or
remove things from environments that have positive/negative effects
o May use info to treat disorders.
Studying Genetic Material:
o Studies that look for patterns of inheritance of genetic markers in large
families in which a particular condition is common.
o Segment of DNA that varies among individuals, has a known location on a
chromosome, and can function as a genetic landmark for a gene.
Linking genes and behaviour:
Even when researcher locate a gene on a chromosome, they do not automatically
know its role in physical or psychological functioning.
Most human traits are influenced by more than one gene pair (polygenic); from
simple to complex traits.
Our human heritage: courtship and mating:
o Interdisciplinary field that emphasized evolutionary explanations of
social behaviour in animals and humans.
o We have a tendency to act in ways that maximize changes of passing on
genes as well as helping close biological relatives do the same.
Evolution and Sexual strategies:
Differences in survival and mating problems have ef to differences in aggression,
dominance and sexual strategies between sexes… the original argument is as
o Males compete with other males to access females, inseminate as many as
o Females have larger biological investment in pregnancy so they choose
dominant males with resources and status.
Evolution and Preferences: Cross cultural studies have found consistent differences between males and
o Mating preferences such as in age predict status and dominance in men
and fertility in women.
People vary a lot:
Different cultures have different sexual behaviours and marital roles.
Some places men have:
o Lots of kid, lots of wives
o One wife, involved in parenting; or not allowed to marry.
Some places, women have:
o Lots of kids, stay at home,
o To be chaste, other places its both sexes or neither.
o In one group of women are polyandrous
Why did the data support the idea that men were promiscuous and women selective?
Convenience sample of university students
Often only asked women what their preferences were.
When they started asking men they found that even more men though
monogamy was preferential to promiscuity!
So the data had been oversimplified.
More Issues on sociobiology:
Men “should” be more jealous but aren’t.
o Should be concerning about whether or not their resources are going to
their actual offspring.
Also, the idea that we have “evolved” gender roles is problematic because people
The Fred Flintstone problem:
Humans have changed since we may have has an advantage if we were
promiscuous ales and picky females.
Smell, taste, hone structure changed, maybe when we started with agriculture
Also, we currently know a lot more people than we did 11,000 years ago, so
social factors are different.
Shouldn’t assume that evolutionary theory can explain mate selection in 2013. Genes and Behaviour:
The nature/nurture issue is not clear cut.
One other applied example of the debate between nature and nurture is the issue
Behaviourists and Language:
In the early 20 century behaviourists presumes that all language was
o Reinforced for using it correctly.
Getting needs met (primary reinforce)
Praise (secondary reinforce)
Parents would correct incorrect use of language.
o Could use primary or secondary punishers.
Our Human Heritage: Language:
o A system that combines meaningless elements such as sounds or gestures
to form structured utterances that convey meaning.
o Surface structure:
The way a sentence is spoke.
o Deep structure:
How a sentence is to be understood.
Evidence Supporting Chomsky:
Children in different cultures go through similar stages of linguistic development
Children combine words in ways that adults never would.
Adults do not consistently correct their children’s syntax (grammar), yet
children learn to speak correctly anyways.
Children not exposed to adult language might invent a language of their own.
Infants as young as 7 months can derive simple linguistic rules from a string of
Learning and Language:
Other scholars argue environment plays larger role in language (not all innate)
o Computer neutral networks: Mathematical models of the brain that can “learn” some aspects of
o Other augments:
Major differences in acquisition, parents recast sentences rather
than corrections, children imitate recasts and expansions.
Higher number means genes explain variability
o Does not mean that genes CAUSE variability.
o Very important point.
o When environments are very similar then heritability goes up.
o VARIATION can’t be explained by environment anymore.
o Tells you hat accounts for variability, not causation.
o Genes or environment
Just because you get a gene does not mean you ill get the disorder, it just means
all variation in the disorder can be explained by genes not environment.
o E.g. best example for psychology is PKU… its entirely genetic but
avoidable if you avoid certain foods.
As genes become less variable the impact of the environment becomes a better
explanation of variability.
Heritability is all about variation.
Inheritance is all about the lack of variation.
When psychologists talked about heritability what they are talking about is
almost entirely useless to us! Chapter 3 2/5/2013 11:01:00 AM
Genes, Evolution, and the Environment:
Unlocking the secrets of genes:
Genes: basic units of heredity, located on chromosomes.
Chromosomes: rod-shaped structures found in the center (nucleus) of every
cell in the body.
o Each sperm cell and egg cell contains 23 chromosomes which equals to
46 chromosomes and 23 pairs.
Chromosomes consist of threadlike strands of DNA molecules, and genes consist
of small segments of this DNA.
Genome: the full set of genes in each cell of an organism (with the exception of
sperm cells and egg cells).
Within each genes, four basic chemical elements of DNA—the bases adenine,
thymine, cytosine, and guanine (A,T,C,G)—are arranged in a particular order
which together constitute a code for the synthesis of one of the many proteins
that affect virtually every aspect of the body, from its structure to the chemicals
that keep it running.
Genetic marker: a segment of DNA that varies among individuals, has a known
location on a chromosome, and can function as a genetic landmark for a gene
involved in a physical or mental condition.
Researchers have identified the sequence of nearly all 3 billion units of DNA and
have been able to determine the boundaries between genes and how the genes
are arranged on the chromosomes. (Human Genome Project)
Usually locating a gene is just the first tiny step in understanding what it does
and how it works.
The Genetics of Similarity:
Evolution and Natural Selection:
Evolution is basically a change in gene frequencies within a population, a change
that typically takes place over many generations. As particular genes become
more common, or less common, in the population, so do the characteristics they
Why do gene frequencies in a population change?
o During the division of the cells that produce sperm and eggs, if an error
occurs in the copying of the original DNA sequence, genes can
spontaneously change, or undergo mutation. During the formation of a sperm or egg, small segments of generic material cross
over (exchange places) from one member of a chromosome pair to another,
before the final cell division.
According to the principle of natural selection, the fate of these genetic
variations depends on the environment.
o If, in a particular environment, individuals with a genetically influenced
trait tend to be more successful than other individuals in finding food,
surviving the elements, and fending off enemies—and therefore better at
staying alive long enough to reproduce—their genes will become ore and
more common in the population.
o Their genes will have been “selected” by reproductive success, and over
many generations these genes may eve spread throughout the species.
Individuals whose traits are not as adaptive in the struggle for
survival will not be as “reproductively fit”: they will tend to de before
reproducing, and therefore their genes, and the traits influenced by
those genes, will become less and less common and eventually may
However, this “survival of the fittest” account of evolution cannot explain all the
physical and behavioural traits that reflect a genes success (that is, increase or
decrease within a population).
In natural selection, nature determines which genes survive and reproduce, and
which genes disappear from the planet.
In sexual selection, the members or either the other sex or the same sex, with
which one is