Chapter 9: Evolution and Behavior
Communication, cooperation, and conflict in the animal world
Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives
Be able to explain the following:

Behaviors are traits that can evolve

Cooperation, selfishness, and altruism can be
better understood with an evolutionary approach

Sexual conflict can result from disparities in
reproductive investment by males and females

Communication and the design of signals evolve
Behaviors are
traits that can
evolve.
9.1 Behavior has adaptive value, just
like other traits
Animals should
maximize energy
consumed and
minimize energy
used
Humans like to eat foods high in
fat and sugar.
Why do species have taste preferences?
 Feeding
 Living
choices directly influence fitness.
and reproducing require energy.
 Maximal
extraction of energy and
acquisition of essential nutrients
 Natural
selection can shape feeding
behavior.
Behavior
• Behavior encompasses any and all of the
actions performed by an organism, often
in response to its environment or to the
actions of another organism.
• Feeding behavior is only one of many
behaviors influenced by natural selection.
Scope of Animal Behavior
• Conflict, aggression, and territoriality
• Cooperation, alliance building, and
sociality
• Competing for food and avoiding
predators
• Migration and navigation
• Behavioral control of body temperature
Scope of Animal Behavior
• Courtship and mate choice
• Pair bonding and fidelity
• Breeding and parental behavior
• Communication
• Learning and tool use
Take-home message 9.1
 Behavior
encompasses any and all of the
actions performed by an organism.
 When
a heritable trait increases an
individual’s reproductive success relative
to that of other individuals, that trait tends
to increase in frequency in the population.
Take-home message 9.1
 Behavior
is as much a part of an
organism’s phenotype, and as such it can
be produced and shaped by natural
selection.
9.2 Some behaviors are innate.
Nearly all physical traits of all organisms are
the products not only of genes but also of
environmental conditions.
Role of the Environment
 The
degree to
which a behavior
depends upon the
environment varies
a great deal.
 Instincts
or
innate behaviors
 Example:
Fixed
action pattern
Fixed Action Pattern
 Triggered
under
certain conditions
 Requires
learning
 Does
 Once
no
not vary
started, runs
to completion
Take-home message 9.2

Like any physical trait, behavior can depend on
the environment for expression, though the
degree of that dependence varies.

Instincts, or innate behaviors, develop without
any environmental input.

They are behaviors that are present in all
individuals in a population and do not vary much
from one individual to another or over an
individual’s life span.
Take-home message 9.2
• A fixed action pattern, a type of innate
behavior, is a sequence of behaviors that
requires no learning, does not vary, and
runs to completion once started.
9.3 Some behaviors must be
learned (and some are learned
more easily than others).
Learning
 Involves
behaviors that are altered and
modified over time in response to past
experiences
 Tremendous
variation among behaviors
that require learning
• Some are easy to learn
• Others are not
Production of Behaviors
and the Role of the Environment
 Primates—fear
 Appears
of snakes
not innate, but learned
Prepared Learning
Behaviors that are learned easily and by all
(or nearly all) individuals


Snake-fearing behavior of monkeys
Acquisition of language in humans
Q
Why is it so much easier for
an infant to learn a complex
language than for a college
student to learn biology?
Examine the evolutionary basis for the
acquisition of certain behaviors.
Prepared Learning
 However,
organisms don’t learn everything
with equal ease.
Q
Human
babies quickly
and easily develop
a fear of snakes.
Yet they don’t
easily develop a
fear of guns.
Why?
Take-home message 9.3
 In
contrast to innate behaviors are those
behaviors that are influenced more by the
individual’s environment.
 These
behaviors require some learning
and are often modified over time in
response to past experiences.
Take-home message 9.3
 Organisms
are well-prepared to learn
behaviors that were important to the
reproductive success of their ancestors.
 Organisms
are less prepared to learn
behaviors irrelevant to their evolutionary
success.
9.4 Complex-appearing
behaviors don’t require complex
thought in order to evolve.
“I must maximize my
reproductive success!”
 Why
do animals have sex?
 Why
do people have sex?
Q
Do animals consciously
act in order to improve
their reproductive
success?
Evolutionary Psychology
“In the distant future I see open fields for far more
important researches. Psychology will be based on
a new foundation.”
Charles Darwin, On the Origin of Species
Take-home message 9.4
 If
certain behavior in natural situations
usually increases an animal’s relative
reproductive success, the behavior will be
favored by natural selection.
 The
natural selection of such behaviors does
not require the organism to consciously try
to maximize its reproductive success.
Cooperation,
selfishness, and
altruism can be
better understood
with an
evolutionary
approach.
9.5 “Kindness” can be explained
 Does
unconditional love exist in the animal
kingdom?
 Altruistic
behaviors—behaviors that
come at a cost to the individual doing the
behavior while benefiting the recipient.
Darwin’s Theory
 Natural
selection generally works to
produce selfish behavior.
 Altruistic-appearing
 Fatal
to his theory?
behavior is common.
Apparent Acts of Altruism
 Kindness
selection
 Kindness
toward close relatives: kin
toward unrelated individuals:
reciprocal altruism
Take-home message 9.5
 Many
behaviors in the animal world
appear to be altruistic.
 In
almost all cases, the apparent acts of
altruism are not truly altruistic; they have
evolved as a consequence of either kin
selection or reciprocal altruism and, from
an evolutionary perspective, are beneficial
to the individual engaging in the behavior.
9.6 Apparent altruism
toward relatives can evolve
through kin selection.
Hamilton’s Rule
 Altruistic-appearing
behavior will occur
when the benefits to close relatives are
greater than the cost to the individual
performing the behavior.
are really acting in their own
genes’ best interests.
 They
Redefining an Individual’s Fitness
 Direct
fitness
• An individual’s total reproductive output
 Indirect
fitness
• The reproductive output brought about by
altruistic behaviors toward close kin
 Inclusive
fitness
• The sum of an individual’s indirect and direct
fitness
Conflicts
 Because
different individuals do not share
all of the same alleles, we should always
expect some conflict.
 Example:
gestational diabetes
Kin Selection & Conflict
• The less closely related two individuals
are, the more likely they are to experience
conflict.
– Male lions
• “Cinderella syndrome”
Take-home message 9.6
• Kin selection is apparently-altruistic behavior
in which an individual that assists a genetic
relative compensates for its own decrease in
direct fitness by helping increase the
relative’s fitness and, consequently, its own
inclusive fitness.
9.7 Apparent altruism toward
unrelated individuals can evolve
through reciprocal altruism.
Vampire Bats
 In
many cases, individuals give blood to
unrelated individuals.
 How
might this behavior have arisen?
Are they repaid the favor?
Reciprocal Altruism
Storing goodwill
Certain Conditions Must Be Met
1) Repeated interactions among individuals
2) The benefits to the recipient must be
significantly greater than the costs to the
donor.
3) The ability to recognize and punish
cheaters
Q
Why are humans among
the few species to have
friendships?
Q
Why is it easier to
remember gossip than
physics equations?
Take-home message 9.7
 In
reciprocal altruism, an individual
engages in an altruistic-appearing act
toward another individual.
• Although giving up something of value,
the actor does so only when likely to get
something of value at a later time.
Take-home message 9.7

Reciprocal altruism occurs only if:
•
•
•

individuals have repeated interactions
benefits to the recipient are much greater
than costs to the donor
individuals can recognize and punish
cheaters
These conditions are satisfied in humans
but in few other species.
9.8 In an “alien” environment,
behaviors produced by natural
selection may no longer be
adaptive.
Mismatch
• Between the environment organisms are
in and the environment to which they are
evolutionarily adapted.
Take-home message 9.8
• When there is a mismatch between the
environment organisms are in and the
environment to which they are adapted,
the behaviors they exhibit are not
necessarily evolutionarily adaptive.
9.9 Selfish genes win out
over group selection.
Does evolution ever lead to behaviors
that are good for the species or
population but detrimental to the
individual exhibiting the behavior?
Take-home message 9.9
 Behaviors
that are good for the species or
population but detrimental to the fitness
of the individual exhibiting such behaviors
are not generally produced in a population
under natural conditions.
Sexual conflict
can result from
disparities in
reproductive
investment by
males and
females.
9.10 There are big differences
in how much males and
females invest in reproduction.
Definition of “Male” and “Female”
A
female produces the larger gamete.
 A male produces the smaller gamete.
 The
mother’s material contribution to the
offspring exceeds the father’s.
Evolution of Differences in
Male/Female Behaviors
Extent of energetic differences in their
reproductive investment.
Why do males
usually compete
for females rather
than the opposite?
Q
Why do males usually
compete for females
rather than the opposite?
Male and female reproductive
investment differs across species
Examples:
 Mammals
• Gestation internal
• Lactation
Male and female reproductive
investment differs across species
Examples:
 Birds
• Gestation external
• No lactation
Male and female reproductive
investment differs across species
Examples:
 Fish and
amphibians
• External fertilization
Evolution of Differences in
Male/Female Behaviors
1) Extent of energetic differences in the
reproductive investment
2) Paternity uncertainty
• also has profound influence on reproductive behavior
Take-home message 9.10
 In
mammals and many other animals,
there are important differences between
males and females relating to
reproduction.
Take-home message 9.10
 Fertilization
female.
 Lactation
 In
usually takes place in the
occurs only in the female.
species where fertilization occurs inside
the female, males cannot be certain that
offspring are their progeny.
Take-home message 9.10
 These
physical differences have led to the
evolution of differences in male and
female reproductive behavior.
9.11 Males and females are
vulnerable at different stages
of the reproductive exchange.
Predictions About Sex-Related
Behavior
1) The sex that invests more will be more
discriminating.
2) The sex that invests less will compete
amongst themselves for access to the
higher-investing sex.
Potential Exploitation at Different
Stages of the Reproductive
Process
 At
the point of mating
 At
the point of parental care to offspring
Two Critical Points To Keep
In Mind
1. There is tremendous variability across
species in male and female behaviors.
2. Throughout history, there have been
many cases of people using observations
and scientific findings to justify a wide
variety of discriminatory thoughts and
behaviors.
Take-home message 9.11
• Differing patterns of investment in
reproduction make males and females
vulnerable at different stages of the
reproductive process.
• This has contributed to the evolution of
differences in their sexual behavior.
Take-home message 9.11
• The sex with greater energetic investment
in reproduction is more discriminating
about mates, and members of the sex
with a lower energetic investment in
reproduction compete among themselves
for access to the higher-investing sex.
9.12 Tactics for getting a
mate: competition and
courtship can help males
and females secure
reproductive success.
Take-home message 9.12
 As
a consequence of male-female
differences in initial reproductive
investment, males tend to increase their
reproductive success by mating with many
females and have evolved to compete
among themselves to get the opportunity
to mate.
9.13 Tactics for keeping a mate:
mate guarding can protect a male’s
reproductive investment
 When
offspring survival can be enhanced
with greater parental investment…
Tactics for Keeping a Mate:
Mate Guarding

When offspring survival can be enhanced
with greater parental investment…
there is an incentive for males to provide
some parental care…makes him
vulnerable to paternity uncertainty.

Tactics for Keeping a Mate:
Mate Guarding
 When
offspring survival can be enhanced
with greater parental investment…
 there
is an incentive for males to provide
some parental care…
 even
though such behavior makes him
vulnerable to paternity uncertainty.
Q
Why do so few females guard their
mates as aggressively as males
do?
 Mate
guarding in order to reduce
vulnerability
 Attempt to reduce paternity uncertainty
 “Danger zone” for males
Mate Guarding:
From Simple to Macabre
Copulatory Plugs
 Reptiles,
species
insects, and many mammalian
 Males
block the passage of sperm into the
female
 Coagulated
sperm and mucus
Take-home message 9.13
 Mate
guarding can, in general, increase
reproductive success by reducing
additional mating opportunities for a
partner…
 …and
can improve a male’s reproductive
success by increasing his paternity
certainty and thus reducing his
vulnerability when he makes investment in
offspring.
9.14 THIS IS HOW WE DO IT
When paternity uncertainty
seems greater, is paternal
care reduced?
The System
• Bluegill sunfish in lakes and rivers in North
America.
• Males guard eggs.
• “Cuckold males.”
Experiment 1
• 34 randomly chosen nests.
• Cuckold males under a glass container,
visible to by male in nest.
• Predator fish under a glass container.
• Parental care evaluated.
Would you expect the presence of
cuckold males to influence a nest
owner’s perception of paternity
certainty?
• Prediction a: The presence of the cuckold
males should reduce the nest owner’s
paternity certainty and therefore reduce
his egg-guarding efforts.
Should the presence of cuckold males
influence a nest owner’s perception of
paternity certainty after the offspring
hatch?
Why or why not?
• Prediction b: After the offspring hatch, the
nest owner can determine whether they
are his genetic offspring, so he should not
exhibit any reduction in parental care
relative to males in the control group.
Results of Experiment 1
Parental Care Score
Egg Guarding
Offspring Guarding
Prediction
Reduced
Unchanged
Actual Results:
• No rivals (control)
80 ± 10
90 ± 10
• Rivals present
52 ± 7
95 ± 10
Change in care
Reduced
Unchanged
How much did the presence of cuckold males
reduce egg guarding?
How much did it alter offspring guarding?
Experiment 2
• 20 randomly chosen nests.
• Removal of one-third of the eggs from
each nest and replacement with unrelated
fertilized eggs from another male’s nest.
• Predator fish under a glass container.
• Parental care evaluated.
Should a nest owner show reduced
parental care of eggs that were
swapped in from another nest?
Why or why not?
• Prediction a: Prior to hatching of the eggs,
the nest owner should exhibit the same
egg-guarding efforts regardless of
whether or not the eggs were swapped.
Should a nest owner show reduced
parental care of hatched offspring
after eggs were swapped?
Why or why not?
• Prediction b: After the offspring hatch,
because the nest owner can determine
whether they are his genetic offspring, he
should exhibit reduced parental care
relative to the control males.
Results of Experiment 2
Parental Care Score
Prediction
Egg Guarding
Offspring Guarding
Unchanged
Reduced
Actual Results:
• Eggs not swapped 90 ± 10
(control)
73 ± 9
• Eggs swapped
95 ± 10
50 ± 8
Change in care
Unchanged
Reduced
How much was egg guarding reduced when unrelated
eggs were swapped into the nest?
How much was offspring guarding changed?
What conclusions can you draw from these results?
Take-home message 9.14
• Experimental manipulations of the cues of
paternity certainty can increase or
decrease a male’s parental investment in
accordance with the prediction that
decision making about parental
investment reflects perceptions of genetic
relatedness.
9.15 Monogamy versus polygamy:
mating patterns can vary across
human and animal cultures.
Mating Systems
 Polygamy
• when some individuals attract multiple mates
while other individuals attract none
 Monogamy
• most individuals mate and remain with just
one other individual
Mating Systems
Polygamy subdivided into:
 Polygyny
• individual males mate with multiple females
 Polyandry
• individual females mate with multiple males
Mating Systems Are Not Easy to Define
Three issues complicate the task:
1) differences between animals’ mating
behavior and bonding behavior
Pair bond—appears monogamous
Mating Systems Are Not Easy to Define
Three issues complicate the task:
2) mating system variation within the
species
Mating Systems Are Not Easy to Define
Three issues complicate the task:
3) males and females vary in their mating
behavior
Examination of Birds and Mammals Reveals
One Sharp Split
Are humans monogamous or
polygamous?
Take-home message 9.15
 Mating
systems—monogamy, polygyny,
polyandry—describe the variation in
number of mates and the reproductive
success of males and females.
 They
are influenced by the relative
amounts of males’ and females’ parental
investment.
9.16 Sexual dimorphism is an
indicator of population’s mating
behavior.
Body Size Is an Important Clue
to Behavior
 Selection
for larger and larger body size
when competition is high
 Coloration
can also be a clue to behavior
 Male-male
competition sometimes results in
differences in physical appearance between
the sexes
It’s almost impossible to
distinguish males from
females in most bird species.
Why does that mean they are
monogamous?
Men are bigger than women.
What does that tell us about our
evolutionary history of monogamy versus
polygamy?
Take-home message 9.16
 Differences
in the level of competition
among individuals for mating opportunities
can lead to male-female differences in
body size and other aspects of
appearance.
Take-home message 9.16
 In
polygynous species, this results in
larger males that are easily distinguished
visually from females.
 In
monogamous species, there are few
such differences between males and
females.
Communication
and the design
of signals
evolve.
9.17 Animal
communication and
language abilities evolve.
Chemical Communication in Animals
Communication
 An
action or signal on the part of one
organism that alters the behavior of
another organism.
 What
types of animal behavior require
communication?
 What
use?
types of communication do animals
Types of Animal Communication
Chemical
Acoustical
Visual
Complex Forms of Communication
Honeybee waggle
dance
What is language?
How is language identified?
Honeybees
 American Sign Language taught to orangutans
 Human language

Take-home message 9.17
 Methods
of communication—chemical,
acoustic, and visual—have evolved among
animal species, enabling them to convey
information about their condition and
situation.
 These
abilities influence fitness and the
evolution of almost all other behaviors.
9.18 Honest signals reduce
deception.
Conveying accurate information
Honest Signal
 Cannot
be faked
 Given
when both the individual making the
signal and the individual responding to it
have the same interests
 Carries
the most accurate information about
an individual or situation
Deception Evolves!
 “Begging”
allele
 Evolutionary
“arms race”
• Unambiguous signals
• Sophisticated patterns of deception
 An
organism’s phenotype includes its
behaviors
Take-home message 9.18
 Animals
have evolved to rely primarily on
signals that cannot easily be faked, in
order to gain the maximum amount of
information.