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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
 Selfishness, cooperation, and altruism
 Communication and the design of signals
 Reproductive investment and sexual conflict
 Parental care and mating systems

Animals should maximize energy
consumed and minimize energy used.
1) Behavior has
adaptive value
just like other
traits.
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.
Behaviors can be influenced by natural
selection.
 Feeding
behavior
• Humans; starlings; shore crabs examples
 Maternal
care
• Mice example
 Singing
behavior
• Songbirds example
Effects of evolution by natural selection
are all around.
 Peacock
feathers
 Cryptic coloration observed in many
species
BEHAVIOR is part of an organism’s
phenotype.
• also under the influence of natural selection
Take-home message 9.1
 Behavior
is any and all actions performed
by an organism.
 Behavior
is as much a part of an
organism’s phenotype as is an anatomical
structure.
 Behavior
is produced and shaped by
natural selection.
9.2 Some behaviors are innate.
Genes and the Environment
 The
production of a trait is not completely
genetically determined.
 Certain
environmental conditions are also
required.
Role of the Environment
 The
degree to which a
behavior depends
upon the environment
varies a great deal.
 Instincts
or innate
behaviors
 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

The degree to which a behavior depends on the
environment varies a great deal.

Instincts and innate behaviors are present in all
individuals in a population and do not vary much
from one individual to another.

Innate behaviors don’t require environmental
input to develop.
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
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.
Take-home message 9.3
 In
contrast to innate behaviors are
behaviors that are influenced more by the
environment.
 These
behaviors require some learning
and are often altered and modified over
time in response to past experiences.
Take-home message 9.3
 Organisms
are well-prepared to learn
behaviors that have been 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?
Animals don’t consciously try to
maximize their reproductive
success, yet they behave as if
they do?
How do they do it?
Rules of Thumb
 Relatively
easy-to-follow responses to cues
that reliably lead to a desired outcome
Rules of Thumb
 Pleasures,
success
 Not
incentives, and reproductive
necessary for the animal to be
consciously seeking that outcome
How do we
know?
Tricking animals
Unrelated people who grow up
together from infancy on the same
kibbutz never marry each other?
Why?
Take-home message 9.4
 If
an animal’s behavior in natural
situations usually increases its relative
reproductive success, the behavior will be
favored by natural selection.
 The
natural selection of behaviors does
not require an organism to consciously try
to maximize its reproductive success.
9.5 A general theory of “kindness”
helps explain the evolution of
apparent acts of altruism.
 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
 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 altruistic.
 In
almost all cases, these are not really
acts of altruism and have evolved as a
consequence of either kin selection or
reciprocal altruism.
 These
behaviors 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
Who are people most likely
to bequeath money to upon
their death?
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
Take-home message 9.6
 Kin
selection describes behavior in which
an individual assists its genetic relative.
 Although
the individual’s direct fitness
decreases, the relative’s fitness increases.
 Thus,
the individual’s inclusive fitness
increases.
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
We’re all born with a spare kidney,
yet virtually no one donates theirs
to non-relatives in need.
Why?
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
Why are humans among
the only species to have
friendships?
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.
 The
actor only gives up something of
value when likely to get something of
value later.
Take-home message 9.7

Reciprocal altruism occurs only if:
•
•

individuals have repeated interactions
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.
Behaviors favored by natural selection
over evolutionary time can cause
individuals to behave in a way that
reduces their fitness.



Belding’s ground squirrels
Craving high-fat foods
Donations to refugees
Take-home message 9.8
 When
organisms are in environments that
differ from 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 for the good of the species or population,
while being detrimental to the individual?
Take-home message 9.9
 Behaviors
that are good for the species or
population but detrimental to the
individual are not generally produced in a
population under natural conditions.
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
1) Extent of energetic differences in the
reproductive investment.
Why do males
usually compete
for females
rather than the
opposite?
Differences in Reproductive
Investments
 Fertilization
 Lactation
within the female
in female mammals
Offsets and Reversals
in Reproductive Investment
Examples:
 Birds
• Gestation external
• No lactation
Offsets and Reversals
in Reproductive Investment
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 types of
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
Take-home message 9.11
 Differing
patterns of investment in
reproduction make males and females
vulnerable to exploitation at different
stages.
 This
has contributed to the evolution of
differences in sexual behavior.
Take-home message 9.11
 The
sex with the greater investment is
more discriminating about mates.
 The
sex with less investment competes for
access to the higher-investing sex.
9.12 Tactics for getting a
mate: competition and
courtship
Take-home message 9.12
 Males
tend to increase their reproductive
success by mating with many females and
have evolved to compete for the
opportunity to mate.
 Females
tend to increase their
reproductive success by caring for their
offspring and being choosy about selecting
a 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…
• even though such behavior 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.
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
 Because
paternity certainty is low in
animals with internal fertilization, males
that provide parental care are vulnerable
to loss of their investment.
 Mate
guarding and other tactics have
evolved to increase paternity certainty.
9.14 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 9.14
 Mating
systems—monogamy, polygyny,
polyandry—describe the variance in mate
number of males and females.
 They
are influenced by the relative
amounts of parental investment by males
and females.
9.15 Sexual dimorphism is an
indicator of population mating
behavior.
Body Size Is an Important Clue
to Behavior
 Level
of competition among the individuals
of each sex
 Selection
for larger and larger body size
when competition is high
It’s almost impossible to
distinguish males from
females among 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 9.15
 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 9.15
 In
polygynous species, this results in
larger males that are easily distinguished
from females visually.
 In
monogamous species, there are few
such differences between males and
females.
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?

Vervet monkeys

American Sign
Language taught
to chimpanzees
and gorillas

Human language
Take-home message 9.16
 Methods
of communication have evolved
among animal species, enabling them to
convey information.
 These
abilities influence fitness and the
evolution of virtually all other behaviors.
9.17 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 9.17
 Animals
have evolved to rely primarily on
signals that cannot easily be faked in
order to gain the maximum amount of
information from them.