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CHAPTER 3:
Genetic and Evolutionary Foundations of Behavior
Why Genetics?
•Behavior is hereditary!
•Our environment has shaped our
behavior across generations 
EVOLUTION
•We can learn much about our
behavior by studying our animal
relatives
•Did you know: we share
98.8% of our genes with
chimpanzees?
•50% with a banana
How Genes Affect Behavior
 GENE: the basic physical
unity of heredity
 Genes code for protein
molecules
 Structural proteins
 Enzymes – control the
rate of every
chemical reaction in
every cell
 Genes are composed of
long molecules called
DNA (deoxyribonucleic
acid)
From Cells to Genes…
chromosome
DNA
cell
gene
nucleus
Genes Provide the Code for Proteins
 Proteins are comprised of
amino acids
 Coding vs. “junk” DNA
 CODING GENES: code for
unique protein molecules
 REGULATORY GENES: help
activate or suppress specific
coding genes and thereby
influence the body’s
development
 Genes do not “code for”
behaviors.
Gene/Environment Interaction
 ENVIRONMENT: every aspect of an individual and his or
her surroundings except the genes themselves.
Geneticists use the term genotype to refer to the set of genes that the
individual inherits and the term phenotype to refer to the observable
properties of the body and behavioral traits.
Genes and Replication: Mitosis
 MITOSIS: the form of cell
division involved in
normal body growth,
which produces cells
that are genetically
identical to each other
 MEIOSIS: The form of cell
division involved in
producing egg or sperm
cells, which results in cells
that are genetically
dissimilar and that each
have half the number of
chromosomes of the
original cell.
The Genetic Diversity of
Offspring
 ZYGOTE: The single cell that is formed when an egg and
sperm cell unite
Consequences of Gene Pairing
 LOCUS: a position on a chromosome that contains the
DNA of a single gene
 ALLELES: different genes that can occupy the same locus
on a pair of chromosomes and can potentially pair with
one another
 Homozygous vs. heterozygous
 Dominant vs. recessive
Consequences of Gene Pairing
Mendelian Genetics
Gregor Mendel, Mid-19th Century
Mendelian Genetics
Polygenic Characteristics
 POLYGENIC CHARACTERISTICS: any trait or characteristic
for which the observed variation is affected by many
genes
 SELECTIVE BREEDING: the mating of those members of a
strain of animals or plants that manifest a particular
characteristic to affect the genetic makeup of future
generations of that strain
Evolution by Natural Selection
 NATURAL SELECTION:
selective breeding
that results from the
obstacles to
reproduction that are
imposed by the
natural environment
Genetic Variability
• Genes are reshuffled during DNA
recombination and meitotic division
• Errors that occasionally and unpredictably
occur during DNA replication, producing a
“replica” that is different from the original
Environmental Influence on
Natural Selection
 Evolution is contingent on
environmental change
 Evolution can progress slowly,
rapidly, or almost not at all
 More complex changes require
much more time
 All species are to varying
degrees similar to one another
because of common ancestry,
and all species are to some
degree unique because natural
selection has adapted each
species to the unique aspects of
the environment in which it lives
and reproduces.
Evolution in Action
Before the industrial
revolution, a uniformly
dark variant of the
peppered moth made
up 2% of the species.
After the industrial
revolution, 95% of
peppered moths showed
this dark coloration.
Skinks living on the
coast tend to lay eggs.
Those skinks living in the
cooler mountains tend
to give birth to live
young.
The Blue Moon Butterfly of
the Samoan islands was
being attacked by a
parasite which destroyed
male embryos. This led to a
gender imbalance
whereby males made up
only 1% of the butterfly
population. However,
within ten generations (~1
year) males had returned
to 40% of the population.
Over time the
bacteria have
become far more
efficient at growing
under the conditions
used. One of the
populations
developed the ability
to utilize citrate as a
nutrient.
• Malaria
• MMR
Mistaken Beliefs about Evolution
Functionalism
 FUNCTIONALISM: a school of psychological thought,
founded by William James and others, that focuses on
understanding the functions, or adaptive purposes, of
mental processes.
•
Why do giraffes have long necks?
•
Why do male songbirds sing?
•
Why do humans have the ability to
learn language?
Functionalistic Explanations of
Behavior
Ultimate Explanation
Proximate Explanation
 Functional explanations at
the evolutionary level; that
is, how the behavior plays
or played a role in survival
and reproduction
 Explanations that deal with
the immediate
environmental conditions
or the mechanisms within
the individual that cause
the behavior to occur
Limitations on Functionalist Thinking
1.
VESTIGIAL CHARACTERISTICS:
inherited characteristics of
anatomy or behavior that are
no longer useful to the species
but were presumably useful at
an earlier time in evolution
•
2.
E.g. appendix, grasp reflex
Some traits are side effects of
natural selection for other
traits
Limitations on Functionalist Thinking
3. Some traits result simply from
chance
•
Variation due to chance
alone without selection is
known as GENETIC DRIFT
4. Evolved mechanisms cannot
deal effectively with every
situation
Species-Typical Behaviors in Humans
• Any behavior pattern that is so characteristic of a given
species of animal that it can be used to help identify that
species
• However, these behaviors are not rigid and uninfluenced
by learning!
The Role of Learning in SpeciesTypical Behaviors
Walking
Language
Biological Preparedness
 BIOLOGICAL PREPAREDNESS: organisms have physical
and anatomical structures that predispose them to
engage in certain (species-specific) behaviors
 The environment
also plays a role!
Cross-Species Comparisons of
Species-Typical Behaviors
 HOMOLOGY: any similarity
among species that exists
because of the species’
common ancestry
Cross-Species Comparisons of
Species-Typical Behaviors
 ANALOGY: any similarity among species that is not due to
common ancestry but has evolved independently
because of some similarity in their habits or lifestyles
Evolutionary Origin of Two Human Smiles
Evolutionary Analyses of Mating Patterns
• One male mates with more than one female
• One female mates with more than one male
• One male mates with one female
• Members of a group consisting of more than one male
and more than one female mate with one anther
Parental Investment
 The time, energy, and risk to survival involved in
producing, feeding and otherwise caring for each
offspring
 In general, for species in which parental investment is
unequal, the more parentally invested sex will be (a)
more vigorously competed for than the other and (b)
more discriminating than the other when choosing mates
Mating Patterns and Parental Investment
POLYGYNY
• High female and low male
parental investment
• Females choose the best
males
• Males must try and mate
with as many females
POLYANDRY
• High male and low female
parental investment
• Tend to be egg layers
• Females are more
aggressive courters
Human Mating Patterns
 Humans fall on the boundary between monogamy and
polygyny
 Long-term mating bonds
Sex Differences in Aggression
 AGGRESSION: fighting and threats of fighting among
members of the same species
 In primates, males are more aggressive than females
 These behaviors are
advantageous
(evolution is not
a moral force)
Violence in Humans
 Humans are no
exception to
aggression and
violence
 Cross-culturally, men
are more aggressive
than women (sexual
jealousy)
 Exception:
female bonobos
Patterns of Helping
 HELPING: any behavior that increases the survival
chance or reproductive capacity of another
individual
 COOPERATION: a type of helping behavior in which
interaction among two or more individuals increases
the survival chance or reproductive capacity of
each individual involved in the interaction
 E.g. living in groups or colonies
Altruism
ALTRUISM: a type of
helping behavior in which
an individual increases the
survival chance or
reproductive capacity of
another individual while
decreasing its own survival
chance or reproductive
capacity
Kin Selection Theory of Altruism
 Apparent acts of altruism have come about
through natural selection because such actions are
disproportionately directed toward close genetic
relatives and thus promote the survival of others
who have the same genes
Reciprocity Theory of Apparent
Altruism
 Apparent acts of altruism have come about through
natural selection because they are actually forms of
long-term cooperation rather than true altruism
Evolutionary Fallacies
Naturalistic Fallacy
Deterministic Fallacy
 The mistaken belief that
whatever is natural (and
particularly whatever is a
product of natural
selection) is right, good or
moral
 The mistaken belief that
genes control, or
determine, behavior in a
manner that is
independent of
environmental influences
 Morality is a product of the
human mind!
 Beware the phrase “more
evolved”
 We humans can control
our environment and
thereby control ourselves!