Discussion Entry

Introduction to Behavioral Ecology• What is a “Darwinian
Approach’ to human
behavior?
• Darwin’s theory of evolution
• The adaptationist approach
• The phenotypic gambit
• Levels of explanation
Behavioral ecology
✤ The goal of a behavioral ecology approach is to try to predict the kind
of behavior we are likely to see given a specific set of environmental
conditions
✤ “Environment” includes the subsistence ecology; predator/prey
ecology; social context; one’s own status (e.g. age); etc.
✤ Some factors in the environment change very slowly or not at all:
e.g.
gravity has functioned in the same way throughout evolutionary
history
✤ Some factors change very rapidly: e.g. a female’s fertility status changes
monthly or seasonally; testosterone levels change throughout the day
Environments of Evolutionary
Adaptedness (EEAs)
✤ The EEA is the environment for which a given trait
was selected
✤ A trait is in equilibrium if the current environment is
that for which the trait evolved; i.e. the trait is
functioning as it should
✤ A trait is in disequilibrium if the current environment
is different from that for which the trait evolved; i.e.
the trait is no longer adaptive
Behavioral ecology rests upon several
assumptions
✤ Organisms are typically well-suited to the environments in which
they live (the phenotypic gambit)
✤ The primary mechanism for genes frequencies to change (i.e. for
biological adaptation to take place) is through reproduction
✤ Organisms that are more efficient in getting resources in any
environment will survive and reproduce better than others
✤ Because we cannot observe genes directly, we rely on the
“proximate correlates” of reproductive success — e.g. resources,
status — to measure efficiency
Behavioral ecology rests upon several
assumptions (con’t)
✤ Organisms do not evolve adaptations to pursue the spread of genes
(which we cannot perceive), but to pursue the proximate correlates
of reproductive success (i.e. to pursue resources, status, sex, etc)
✤ Species in novel environments may find that the proximate
correlates are no longer appropriate; thus the phenotypic gambit
will be false (the behavior observed is not well-suited to the
environment even though it evolved through natural selection)
✤ Humans are not qualitatively different from other animals in terms
of what we “evolved” to do: i.e. obtain and use resources to spread
our genes into the next generation
Two-minute biography of Charles Darwin
• Son of upper-class doctor, medical
school dropout, divinity student
• Avid naturalist and collector; worked
as ship’s naturalist on The Beagle,
1832-36
• Made extensive collections and kept
detailed journal of research and
ideas
• Upon return to London, began going
through his collections, established
network of scientific colleagues
Charles Darwin, 1809-1882
1859: On the Origin of Species
Three Simple Ideas
1. Populations are constrained
by the environment’s ability to
support them
2. Individuals within
populations vary in ways that
affect their ability to survive
and reproduce
3. Variations are transmitted
from parents to offspring
★This is the Theory of Evolution by Natural Selection
Definition
• Fitness (or, Evolutionary Fitness)
‣ n. The probability that the line of descent from an individual with a specific
trait will not die out
‣ Biologists use the word fitness to describe how good a particular genotype
is at leaving offspring in the next generation relative to how good other
genotypes are at it.
‣ An organism’s fitness depends on the environment in which it lives. The
fittest genotype during an ice age, for example, is probably not the fittest
genotype once the ice age is over.
Birds of the Galapagos show us how
natural selection works
Daphne Major
“Darwin’s Finches”
The finches’ beaks demonstrate all
three of Darwin’s postulates
Variation
Affects fitness
Heritability
An example: a drought in 1976-78
changed the environment
Due to drought
conditions,
available seeds
were larger and
harder than in
previous years
Smaller-beaked birds were more likely to
die of starvation during the drought
• The drought is an example of a “selection event,” i.e. when
something occurs in the environment that making individuals
with some characteristics more likely to survive and reproduce
Change in
population
phenotype after
selection event
Characteristics of the population
changed over time
• Large beaked adults
survived better
• Large beaked birds
had large beaked
offspring
• Mean beak size
increased in population
★ This is called Directional Selection
In the absence of a specific selection event,
stabilizing selection maintains the
phenotype
• Birds with very small beaks
can’t find enough food
• Birds with very large beaks
have higher juvenile mortality
• So, selection favors
intermediate beak size
• At equilibrium (when there is
no selection event), selection
will maintain stasis (no
change)
If there is no selection,
characteristics will
“drift” randomly
Definitions
• Phenotype: Any observable
trait of an organism, including
‣ Morphology
‣ Development
‣ Physiological/biochemical
properties
‣ Behavior / products of
behavior
• Genotype: The inherited
instructions carried in the genetic
code
‣ The specific alleles found at
any given DNA locus
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• Distribution is not smooth
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• If you add a second locus,
there are more possible
combinations
• Variation is slightly
smoother
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• If you add a third locus, the
distribution gets even
smoother
• Imagine if there were 10s or
hundreds of loci
Environmental variation smoothes out
the distribution
• Environment affects
expression of genes
• When effect of each
locus is small,
environmental
variation will blur
genetic differences
• Variation can remain
“hidden”
★ Selection acts directly on the phenotype, and only
indirectly on the genotype
But… isn’t it just a theory?
According to the United States National Academy of Sciences:
Some scientific explanations are so well established that no new evidence is likely to alter
them. The explanation then becomes a scientific theory. In everyday language a theory
means a hunch or speculation. Not so in science. In science, the word theory refers to a
comprehensive explanation of an important feature of nature supported by facts gathered
over time. Theories also allow scientists to make predictions about as yet unobserved
phenomena
According to the American Association for the Advancement of Science:
A scientific theory is a well-substantiated explanation of some aspect of the natural world,
based on a body of facts that have been repeatedly confirmed through observation and
experiment. Such fact-supported theories are not “guesses” but reliable accounts of the real
world. The theory of biological evolution is more than “just a theory.” It is as factual an
explanation of the universe as the atomic theory of matter or the germ theory of disease.
Our understanding of gravity is still a work in progress. But the phenomenon of gravity,
If it’s so great, why isn’t it a Law?
• A scientific law can generally be reduced to a mathematical
statement, such as E = mc²; it’s a specific statement based on
empirical data, and its truth is generally confined to a certain
set of conditions. For example, in the case of E = mc², c refers
to the speed of light in a vacuum.
• FYI: The universal law of gravitation is represented by the following equation:
F = G × [(m1m2)/r²], where F is the gravitational force between the two objects, measured in
Newtons. M1 and m2 are the masses of the two objects, while r is the distance between
them. G is the gravitational constant, a number currently calculated to be 6.672 × 10-11 N
m² kg-2
★ Scientific laws describe specific features or events;
Scientific theories provide an explanatory
framework for a wide range of features or events.
Some other things that are “just theories”
• Heliocentrism (Copernicus, 1543): The
heliocentric model is a theory that places the
Sun as the center of the universe, and the
planets orbiting around it.
• Plate Tectonics (Wegener, 1912; Wilson,
1960s): The theory that the outer rigid layer
of the earth (the lithosphere) is divided into
a couple of dozen “plates” that move around
across the earth’s surface relative to each
other, like slabs of ice on a lake.
• Oxygen Theory of Combustion (Lavoisier,
1770s): Replaced the theory of phlogiston,
that every material contained an element of
fire, with one that identified the key role of
oxygen.
• Germ Theory (Pasteur, 1860s): Germ
theory states that many diseases are
caused by the presence and actions of
specific micro-organisms within the body.
So, what is an “adaptationist approach”?
• An adaptationist starts with the
assumption that all organisms are
the result of a selection process that
has favored some phenotypes over
others
• The common phenotype of a
population should therefore be
made up of traits that have, on
average, provided a fitness benefit
to those who had them
• One does not need to know the
actual genetics of the trait to apply
an adaptationist perspective
• The questions we are asking are
“Why does the trait look like it
does?” “What was the adaptive
benefit provided by that trait?”
“What alternative traits would have
provided less fitness benefit?”
★ From an evolutionary perspective, physical,
psychological, and behavioral traits can all be
understood as strategies.
An example: Why do these moths have the
coloring that they do?
An adaptationist answer
✤
Because the moth’s coloring
is the product of natural
selection, we assume that it
must confer some fitness
advantage
✤
That is, in previous
generations, those moths who
had the typical coloring were
more likely to survive and
reproduce than those with
other patterns or colors
“The phenotypic
gambit”
✤
Note that we do not need to
know which genes code for
coloration, or how many
genetic variants there are, to
make this assumption
Using the phenotypic gambit
Some possible hypotheses:
1.We assume that there is a
fitness benefit to the typical
behavior
• Coloration affects their
ability to attract mates
• Coloration affects their
ability to absorb Vitamin D
2.We make hypotheses about
what the benefit may be
✓ A hypothesis is a statement
about the likely relationship
between two variables
• Coloration affects their
ability to find food
• Coloration affects their
ability to avoid predators
(camouflage)
There are two moths in each
of these photographs…
can you see them?
Text
Ecological change produced a change in the
typical phenotype
✤
There is natural variation in the
coloring of peppered moths
✤
Originally, the light-colored
moths were far more common;
they hid on lichen-covered oak
trees
✤
During the industrial
revolution in England,
pollution killed much of the
lichen, and turned the trees
dark with soot
✤
The rare dark moths were now
at an advantage, and became
the more common type in the
environment
✤
With environmental
improvement, the light-colored
moth is again becoming
common
★ This seems to support the
hypothesis that coloration
affects the moths’ ability to
avoid predators
Levels of Explanation
There are different ways to answer the
question “Why do these moths have the
coloring that they do?
1. Ultimate Explanation: The way this phenomenon
affects the survival and/or reproduction of the organism;
why it was favored by natural selection.
2. Proximate Explanation: The immediate way the
phenomenon comes about; e.g. hormones,
environmental triggers
3. Ontogenetic Explanation: How it develops across the lifespan
4. Phylogenetic Explanation: How it developed in the species
We use the same approach to generate hypotheses
about the evolution of human physical traits
For example:
• Bipedality
• Cranial shape
• Dental pattern
• Encephalization (big brains)
• Genital morphology
• Gracile form
• Hairlessness
• etc.
Australopithecus afarensis
Approx. 3.9 – 3 mya
But what about behavior?
• Behavior is much more
complicated than physical
traits because it is
constantly changing in
response to infinite
possible stimuli in the
world
• Can we use the same
adaptationist approach to
try to understand
behavior, including
human behavior??
Using an evolutionary approach to explain
human behavior may seem controversial
• There is a popular conception of natural selection as “selfish,”
“competitive,” “red in tooth and claw”
• There are concerns about the moral and political implications
of evolutionary ideas
• There is skepticism about the power of the process of
evolution to produce complexity
• There is a perception that much of human behavior seems
incompatible with evolutionary theory
• Many people assume that an evolutionary explanation or
approach implies that behavior is genetically predetermined
• There is concern that evolutionary approaches don’t account
for the role of culture and social learning in human life
Next Lecture
• Applying the phenotypic gambit
to behavior
• Addressing popular
controversies and
misconceptions
• Explaining complexity with
natural selection
• Constraints on adaptation
Introduction to Behavioral Ecology
• What is a “Darwinian
Approach’ to human
behavior?
• Darwin’s theory of evolution
• The adaptationist approach
• The phenotypic gambit
• Levels of explanation
Behavioral ecology
✤ The goal of a behavioral ecology approach is to try to predict the kind
of behavior we are likely to see given a specific set of environmental
conditions
✤ “Environment” includes the subsistence ecology; predator/prey
ecology; social context; one’s own status (e.g. age); etc.
✤ Some factors in the environment change very slowly or not at all:
e.g.
gravity has functioned in the same way throughout evolutionary
history
✤ Some factors change very rapidly: e.g. a female’s fertility status changes
monthly or seasonally; testosterone levels change throughout the day
Environments of Evolutionary
Adaptedness (EEAs)
✤ The EEA is the environment for which a given trait
was selected
✤ A trait is in equilibrium if the current environment is
that for which the trait evolved; i.e. the trait is
functioning as it should
✤ A trait is in disequilibrium if the current environment
is different from that for which the trait evolved; i.e.
the trait is no longer adaptive
Behavioral ecology rests upon several
assumptions
✤ Organisms are typically well-suited to the environments in which
they live (the phenotypic gambit)
✤ The primary mechanism for genes frequencies to change (i.e. for
biological adaptation to take place) is through reproduction
✤ Organisms that are more efficient in getting resources in any
environment will survive and reproduce better than others
✤ Because we cannot observe genes directly, we rely on the
“proximate correlates” of reproductive success — e.g. resources,
status — to measure efficiency
Behavioral ecology rests upon several
assumptions (con’t)
✤ Organisms do not evolve adaptations to pursue the spread of genes
(which we cannot perceive), but to pursue the proximate correlates
of reproductive success (i.e. to pursue resources, status, sex, etc)
✤ Species in novel environments may find that the proximate
correlates are no longer appropriate; thus the phenotypic gambit
will be false (the behavior observed is not well-suited to the
environment even though it evolved through natural selection)
✤ Humans are not qualitatively different from other animals in terms
of what we “evolved” to do: i.e. obtain and use resources to spread
our genes into the next generation
Two-minute biography of Charles Darwin
• Son of upper-class doctor, medical
school dropout, divinity student
• Avid naturalist and collector; worked
as ship’s naturalist on The Beagle,
1832-36
• Made extensive collections and kept
detailed journal of research and
ideas
• Upon return to London, began going
through his collections, established
network of scientific colleagues
Charles Darwin, 1809-1882
1859: On the Origin of Species
Three Simple Ideas
1. Populations are constrained
by the environment’s ability to
support them
2. Individuals within
populations vary in ways that
affect their ability to survive
and reproduce
3. Variations are transmitted
from parents to offspring
★This is the Theory of Evolution by Natural Selection
Definition
• Fitness (or, Evolutionary Fitness)
‣ n. The probability that the line of descent from an individual with a specific
trait will not die out
‣ Biologists use the word fitness to describe how good a particular genotype
is at leaving offspring in the next generation relative to how good other
genotypes are at it.
‣ An organism’s fitness depends on the environment in which it lives. The
fittest genotype during an ice age, for example, is probably not the fittest
genotype once the ice age is over.
Birds of the Galapagos show us how
natural selection works
Daphne Major
“Darwin’s Finches”
The finches’ beaks demonstrate all
three of Darwin’s postulates
Variation
Affects fitness
Heritability
An example: a drought in 1976-78
changed the environment
Due to drought
conditions,
available seeds
were larger and
harder than in
previous years
Smaller-beaked birds were more likely to
die of starvation during the drought
• The drought is an example of a “selection event,” i.e. when
something occurs in the environment that making individuals
with some characteristics more likely to survive and reproduce
Change in
population
phenotype after
selection event
Characteristics of the population
changed over time
• Large beaked adults
survived better
• Large beaked birds
had large beaked
offspring
• Mean beak size
increased in population
★ This is called Directional Selection
In the absence of a specific selection event,
stabilizing selection maintains the
phenotype
• Birds with very small beaks
can’t find enough food
• Birds with very large beaks
have higher juvenile mortality
• So, selection favors
intermediate beak size
• At equilibrium (when there is
no selection event), selection
will maintain stasis (no
change)
If there is no selection,
characteristics will
“drift” randomly
Definitions
• Phenotype: Any observable
trait of an organism, including
‣ Morphology
‣ Development
‣ Physiological/biochemical
properties
‣ Behavior / products of
behavior
• Genotype: The inherited
instructions carried in the genetic
code
‣ The specific alleles found at
any given DNA locus
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• Distribution is not smooth
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• If you add a second locus,
there are more possible
combinations
• Variation is slightly
smoother
Complex traits are affected by genes at
many loci
• If only one gene affected
beak depth
‣ + + have largest beaks
‣ – – have smallest beaks
‣ + – have intermediate
beaks
• If you add a third locus, the
distribution gets even
smoother
• Imagine if there were 10s or
hundreds of loci
Environmental variation smoothes out
the distribution
• Environment affects
expression of genes
• When effect of each
locus is small,
environmental
variation will blur
genetic differences
• Variation can remain
“hidden”
★ Selection acts directly on the phenotype, and only
indirectly on the genotype
But… isn’t it just a theory?
According to the United States National Academy of Sciences:
Some scientific explanations are so well established that no new evidence is likely to alter
them. The explanation then becomes a scientific theory. In everyday language a theory
means a hunch or speculation. Not so in science. In science, the word theory refers to a
comprehensive explanation of an important feature of nature supported by facts gathered
over time. Theories also allow scientists to make predictions about as yet unobserved
phenomena
According to the American Association for the Advancement of Science:
A scientific theory is a well-substantiated explanation of some aspect of the natural world,
based on a body of facts that have been repeatedly confirmed through observation and
experiment. Such fact-supported theories are not “guesses” but reliable accounts of the real
world. The theory of biological evolution is more than “just a theory.” It is as factual an
explanation of the universe as the atomic theory of matter or the germ theory of disease.
Our understanding of gravity is still a work in progress. But the phenomenon of gravity,
If it’s so great, why isn’t it a Law?
• A scientific law can generally be reduced to a mathematical
statement, such as E = mc²; it’s a specific statement based on
empirical data, and its truth is generally confined to a certain
set of conditions. For example, in the case of E = mc², c refers
to the speed of light in a vacuum.
• FYI: The universal law of gravitation is represented by the following equation:
F = G × [(m1m2)/r²], where F is the gravitational force between the two objects, measured in
Newtons. M1 and m2 are the masses of the two objects, while r is the distance between
them. G is the gravitational constant, a number currently calculated to be 6.672 × 10-11 N
m² kg-2
★ Scientific laws describe specific features or events;
Scientific theories provide an explanatory
framework for a wide range of features or events.
Some other things that are “just theories”
• Heliocentrism (Copernicus, 1543): The
heliocentric model is a theory that places the
Sun as the center of the universe, and the
planets orbiting around it.
• Plate Tectonics (Wegener, 1912; Wilson,
1960s): The theory that the outer rigid layer
of the earth (the lithosphere) is divided into
a couple of dozen “plates” that move around
across the earth’s surface relative to each
other, like slabs of ice on a lake.
• Oxygen Theory of Combustion (Lavoisier,
1770s): Replaced the theory of phlogiston,
that every material contained an element of
fire, with one that identified the key role of
oxygen.
• Germ Theory (Pasteur, 1860s): Germ
theory states that many diseases are
caused by the presence and actions of
specific micro-organisms within the body.
So, what is an “adaptationist approach”?
• An adaptationist starts with the
assumption that all organisms are
the result of a selection process that
has favored some phenotypes over
others
• The common phenotype of a
population should therefore be
made up of traits that have, on
average, provided a fitness benefit
to those who had them
• One does not need to know the
actual genetics of the trait to apply
an adaptationist perspective
• The questions we are asking are
“Why does the trait look like it
does?” “What was the adaptive
benefit provided by that trait?”
“What alternative traits would have
provided less fitness benefit?”
★ From an evolutionary perspective, physical,
psychological, and behavioral traits can all be
understood as strategies.
An example: Why do these moths have the
coloring that they do?
An adaptationist answer
✤
Because the moth’s coloring
is the product of natural
selection, we assume that it
must confer some fitness
advantage
✤
That is, in previous
generations, those moths who
had the typical coloring were
more likely to survive and
reproduce than those with
other patterns or colors
“The phenotypic
gambit”
✤
Note that we do not need to
know which genes code for
coloration, or how many
genetic variants there are, to
make this assumption
Using the phenotypic gambit
Some possible hypotheses:
1.We assume that there is a
fitness benefit to the typical
behavior
• Coloration affects their
ability to attract mates
• Coloration affects their
ability to absorb Vitamin D
2.We make hypotheses about
what the benefit may be
✓ A hypothesis is a statement
about the likely relationship
between two variables
• Coloration affects their
ability to find food
• Coloration affects their
ability to avoid predators
(camouflage)
There are two moths in each
of these photographs…
can you see them?
Text
Ecological change produced a change in the
typical phenotype
✤
There is natural variation in the
coloring of peppered moths
✤
Originally, the light-colored
moths were far more common;
they hid on lichen-covered oak
trees
✤
During the industrial
revolution in England,
pollution killed much of the
lichen, and turned the trees
dark with soot
✤
The rare dark moths were now
at an advantage, and became
the more common type in the
environment
✤
With environmental
improvement, the light-colored
moth is again becoming
common
★ This seems to support the
hypothesis that coloration
affects the moths’ ability to
avoid predators
Levels of Explanation
There are different ways to answer the
question “Why do these moths have the
coloring that they do?
1. Ultimate Explanation: The way this phenomenon
affects the survival and/or reproduction of the organism;
why it was favored by natural selection.
2. Proximate Explanation: The immediate way the
phenomenon comes about; e.g. hormones,
environmental triggers
3. Ontogenetic Explanation: How it develops across the lifespan
4. Phylogenetic Explanation: How it developed in the species
We use the same approach to generate hypotheses
about the evolution of human physical traits
For example:
• Bipedality
• Cranial shape
• Dental pattern
• Encephalization (big brains)
• Genital morphology
• Gracile form
• Hairlessness
• etc.
Australopithecus afarensis
Approx. 3.9 – 3 mya
But what about behavior?
• Behavior is much more
complicated than physical
traits because it is
constantly changing in
response to infinite
possible stimuli in the
world
• Can we use the same
adaptationist approach to
try to understand
behavior, including
human behavior??
Using an evolutionary approach to explain
human behavior may seem controversial
• There is a popular conception of natural selection as “selfish,”
“competitive,” “red in tooth and claw”
• There are concerns about the moral and political implications
of evolutionary ideas
• There is skepticism about the power of the process of
evolution to produce complexity
• There is a perception that much of human behavior seems
incompatible with evolutionary theory
• Many people assume that an evolutionary explanation or
approach implies that behavior is genetically predetermined
• There is concern that evolutionary approaches don’t account
for the role of culture and social learning in human life
Next Lecture
• Applying the phenotypic gambit
to behavior
• Addressing popular
controversies and
misconceptions
• Explaining complexity with
natural selection
• Constraints on adaptation
The Phenotypic Gambit
✤
Applying the phenotypic
gambit to behavior (reaction
norms)
✤
Addressing popular
controversies and
misconceptions
✤
Explaining complexity through
natural selection
✤
Constraints on adaptation
Geisha women from Japan
Men from the Wodaabe Tribe
Can we apply the phenotypic gambit to
behavior?
✤
Assume that the common
phenotype has, on
average, conferred some
fitness benefit relative to
other phenotypes
✤
An easy task when we’re
talking about a physical
trait, such as camouflaging
colors
✤
Perhaps also easy when
we’re talking about
“instinctive” behaviors,
e.g. reflexes
[Almost] everyone one in this picture is exhibiting a
behavioral adaptation (flinching)
What about more complex behaviors?
✤
Complex social behaviors
include:
‣ Status striving
‣ Responses to authority
‣ Flirting and seduction
‣ Sharing and friendship
‣ Taking care of others
‣ Competing with others
‣ Taking advantage of others
‣ Trade and commerce
‣ Etc., etc., etc……
Behavior is
genetic
✤
Behavior is produced by biological
structures: the central and
peripheral nervous systems,
muscles, neurochemicals,
hormones, etc.
✤
The central nervous system (a
biological structure) also produces
the goals and desires that motivate
behavior (hunger, pain, sexual
desire, etc.)
✤
Biological structures are built by
proteins with instructions encoded
in DNA.
Does this mean we are controlled by
our genes??
✤
NO
✤
Biological Determinism is wrong
‣ It is the idea that our behaviors,
beliefs, and desires are fixed by
genetics
‣ That is, they are like the cringe
reflex when something comes flying
at us; we can’t help it
‣ An example: Men cannot help but
sexually pursue an attractive
woman … WRONG
Genes (usually) do not code directly for
behavior
Biological
determinism
There is a gene
that dictates that
I pick up and
hold my child.
Genes, along with environment, shape the
way our cognitive machine reacts
Biological
foundation of
behavior
✤
Genes shape how our senses work
✤
They shape our sensitivity to social cues
✤
They shape our emotional responses to various inputs
✤
All of these things combine in complicated ways to produce behavior
Reaction norms
✤
Often, it is not the specific phenotype itself (morphological,
physiological, or behavioral) that is encoded in the genes, but the
ability to respond correctly to a variety of contexts (strategy)
✤
Examples in physiology: increased metabolic rate in cold
environments; increased red blood cell concentration, greater lung
size, and smaller body size at high altitudes
‣ Between population differences not due to genetic differences
‣ Environmental exposure initiates specific phenotypic response
✤
Behavior in particular is almost always characterized by a reaction
norm. By definition, behavior is a rapid phenotypic change in
response to the environment.
Let’s look at an example
✤
Soapberry bugs are known for
their sexual stamina
✤
Copulations may last up to 11
days (!), with a minimum duration
of about 3 hours
✤
There are behavioral differences
between soapberry bug
populations:
‣
In some populations, copulation times
are highly variable (sometimes quick,
sometimes prolonged)
‣
In other populations, there is little
variation in copulation time
Variable copulation
duration
Stable copulation
duration
This presents two questions
1. What is the purpose of extended copulatory bouts (what is the
fitness benefit relative to other strategies)?
2. Why is variability favored in one population, while standardized
behavior is favored in the other?
** Note that when assessing the potential fitness benefits
that a particular strategy may confer, you must also
consider the costs of that strategy
Using the phenotypic gambit to
answer Question 1
Some possible hypotheses:
✤
✤
We assume that there is a
fitness benefit to the typical
behavior
• Longer copulation results in
greater fertilization and more
offspring
‣
• Longer copulation reduces the
female’s likelihood of re-mating
afterwards
Extending copulation time
We make hypotheses about
what the benefit may be
• Longer copulation increases the
female’s likelihood of retaining
that male’s sperm
• Longer copulation is a form of
“mate-guarding,” keeping other
males away from the female
A valid hypothesis must provide testable
predictions
Hypotheses
Predictions
•Longer copulation results in greater
fertilization and more offspring
•Females mated to males who engage
in longer copulations have more
offspring
•Longer copulation reduces the female’s
likelihood of re-mating
•Once copulation has ended, females
who engaged in longer copulation are
less likely to mate again
•Longer copulation increases the
female’s likelihood of retaining that
male’s sperm
•Males who copulate longer sire a
greater proportion of a female’s
offspring
•Longer copulation is a form of “mateguarding,” keeping other males away
from the female
•Males will copulate longer when there
is more competition for females
A valid hypothesis must provide testable
predictions
Hypotheses
Predictions
•Longer copulation results in greater
fertilization and more offspring
•Females mated to males who engage
in longer copulations have more
offspring
•Longer copulation reduces the female’s
likelihood of re-mating
•Once copulation has ended, females
who engaged in longer copulation are
less likely to mate again
•Longer copulation increases the
female’s likelihood of retaining that
male’s sperm
•Males who copulate longer sire a
greater proportion of a female’s
offspring
•Longer copulation is a form of “mateguarding,” keeping other males away
from the female
•Males will copulate longer when there
is more competition for females
Deriving novel predictions
✤
If we think the mate-guarding
explanation is correct, we can come
up with novel predictions
✤
E.g. If there is no need for mate
guarding, there will be no evidence
of extended copulatory bouts
✤
E.g. If the degree of mate guarding
needed is constant, there will be no
variation in copulatory bouts
✤
This can help differentiate between
competing hypotheses and help
refine existing hypotheses
Hypothetico-deductive
method
Using the phenotypic gambit to
answer Question 2
One possible hypothesis:
✤
We assume that there is a
fitness benefit to the typical
behavior
‣
✤
Varying copulation time vs.
Not varying copulation time
We make hypotheses about
what the benefit may be
• If there is variation in
competition, it is beneficial to
assess the current environment
and adjust copulation time to
maximize fitness (maximize
reproductive events vs. maximize
reproductive assurance)
• If there is no variation in
competition, energy spent on
assessing the environment and
adjusting copulation time is
wasted; therefore it is more
beneficial to have a fixed
copulation time
Variable sex ratio;
Variable copulation
duration
Stable sex ratio;
Stable copulation
duration
✤
Variable annual rainfall in Oklahoma means there is a lot of variation in sex ratio from
year to year (sex ratio impacts competition: more males = more competition)
✤
Stable annual rainfall in Florida means there is little variation in sex ratio from year to
year, therefore no benefit to being able to adjust copulation time
ype that responds sensitively to varia
We use the same method for thinking about
human behavior
✤
There are some characteristics
that are generally considered to
be sexually attractive:
‣ Secondary sexual characteristics
(e.g. muscularity in men)
‣ Symmetry of features
‣ Clear skin, healthy hair
✤
What fitness benefit did
individuals who had that
preference gain?
This makes sense, so tell me again why
it’s controversial?
✤
There is a popular conception of natural selection as “selfish,”
“competitive,” “red in tooth and claw”
✤
There are concerns about the moral and political implications of
evolutionary ideas
✤
There is skepticism about the power of the process of evolution to
produce complexity
✤
There is a perception that much of human behavior seems
incompatible with evolutionary theory
✤
Many people assume that an evolutionary explanation or approach
implies that behavior is genetically predetermined
✤
There is concern that evolutionary approaches don’t account for the
role of culture and social learning in human life
This makes sense, so tell me again why
it’s controversial?
✤
There is a popular conception of natural selection as “selfish,”
“competitive,” “red in tooth and claw”
✤
There are concerns about the moral and political implications of
evolutionary ideas
✤
There is skepticism about the power of the process of evolution to
produce complexity
✤
There is a perception that much of human behavior seems
incompatible with evolutionary theory
✤
Many people assume that an evolutionary explanation or approach
implies that behavior is
genetically
Selection
canpredetermined
favor behavioral variability
✤
There is concern that evolutionary approaches don’t account for the
role of culture and social learning in human life
Aversion to popular conception of natural
selection
✓ “Nature, red in tooth and claw”
✓ “Competition”
✓ “Survival of the fittest”
✤
The engine that runs evolution
is selection, that is, some types
will be more likely to survive
and reproduce than others
✤
Direct competition is only one
outcome of selection
✤
Natural selection can also favor
cooperative or altruistic traits
This makes sense, so tell me again why
it’s controversial?
✤
There is a popular conception
of can
natural
selection
as “selfish,”
Selection
favor
generosity
and sharing
“competitive,” “red in tooth and claw”
✤
There are concerns about the moral and political implications of
evolutionary ideas
✤
There is skepticism about the power of the process of evolution to
produce complexity
✤
There is a perception that much of human behavior seems
incompatible with evolutionary theory
✤
Many people assume that an evolutionary explanation or approach
implies that behavior is
genetically
Selection
canpredetermined
favor behavioral variability
✤
There is concern that evolutionary approaches don’t account for the
role of culture and social learning in human life
Concerns about the moral and political
implications of evolutionary ideas
Some people interpret adaptationist
explanations as justifications for
certain behaviors
✤ This is called the NATURALISTIC
FALLACY
✤
✓ The false assumption that “nature”
and “morality” are linked
✓ The false belief that if something is
evolutionarily adaptive, it is
morally justified
✓ The false belief that if something is
morally bad, it could not have
evolved by natural selection
This makes sense, so tell me again why
it’s controversial?
✤
There is a popular conception
of can
natural
selection
as “selfish,”
Selection
favor
generosity
and sharing
“competitive,” “red in tooth and claw”
✤
There are concerns about
theismoral
and political
implications
of
This
the Naturalistic
Fallacy
– it’s wrong
evolutionary ideas
✤
There is skepticism about the power of the process of evolution to
produce complexity
✤
There is a perception that much of human behavior seems
incompatible with evolutionary theory
✤
Many people assume that an evolutionary explanation or approach
implies that behavior is
genetically
Selection
canpredetermined
favor behavioral variability
✤
There is concern that evolutionary approaches don’t account for the
role of culture and social learning in human life
Can this simple process generate
complex adaptations?
• Critiques argue the genetic mutations necessary to change an amoeba
into a tapeworm are as unlikely as a monkey typing out the
soliloquies of Shakespeare.
• How about just the phrase, “Methinks it is like a weasel” (Hamlet)?
• Imagine a keyboard with letters A…Z and
space key = 27 characters
• Chance of typing first letter of phrase
correctly = 1/27
• Chance of typing first and second letters
correctly = 1/27 x 1/27
• Chance of typing all 28 letters correctly =
(1/27)28 = 10-40
(BTW, this is not a monkey!)
This is an infinitesimally small chance!
But selection is not random! (Variation
is!)
• Dawkins’ WEASEL experiment
• The “monkey” is replaced by a
computer, changing letters at
random
• Correct letters are “selected”
and retained
1st try
wdlmnlt dtjbkwirzrezlmqco p
10th try
mdldmnls itjiswhrzrhez mecs p
20th try
meldinls it iswprke z wecsle
30th try
methings it iswlike b wecsel
40th try
methinks it is like i weasel
Cumulative Selection
• Each incremental step must be favored by natural selection
• It must confer a fitness benefit, making the organism with that trait
more likely to survive or reproduce than those without it
• “Macroevolution” (big changes) are rare, and almost never beneficial
Limpet:
Directional
information
• Small changes are much more likely to
be adaptive.
• Complex adaptations arise through
many small steps.
Beyrich Split Shell:
Better
directional
information
• Each step must be favored by selection
Spiny Murex:
Better
image
Abalone:
Crude image
Evolution can produce rapid change
• Wolves were domesticated ≈ 15,000 yrs ago in Asia
But where does all that variation
come from?
The Chihuahua problem:
• How is it that some dogs are
smaller than the smallest
wolves if all dogs are
descended from wolves?
One assumption is that evolutionary change is the
product of random mutations in the genetic code
• Mutations are “mistakes” in DNA replication that
alter DNA message; they arise spontaneously
• Rates of mutation are very low
• Mutations are usually deleterious (bad)
Hidden variation resolves the
Chihuahua problem
• Normal sized wolves carry some alleles
for small body size (–) and many +
alleles
• As big wolves die (or people prefer
small ones), frequency of – allelles
increases
• Variation is shuffled, some new
combinations arise
• As – alleles become more common,
more – alleles likely to be combined in a
single individual
• New combinations with more – alleles
will be outside initial range of variation
This makes sense, so tell me again why
it’s controversial?
✤
There is a popular conception
of can
natural
selection
as “selfish,”
Selection
favor
generosity
and sharing
“competitive,” “red in tooth and claw”
✤
There are concerns about
theismoral
and political
implications
of
This
the Naturalistic
Fallacy
– it’s wrong
evolutionary ideas
✤
There is skepticism about the power of the process of evolution to
produce complexity Selection can produce rapid, complex change
✤
There is a perception that much of human behavior seems
incompatible with evolutionary theory
✤
Many people assume that an evolutionary explanation or approach
implies that behavior is
genetically
Selection
canpredetermined
favor behavioral variability
✤
There is concern that evolutionary approaches don’t account for the
role of culture and social learning in human life
We’ll deal with the last two points in
the coming weeks….
Implications from today’s lecture
✤
Although our behavior is not
biologically determined, our
evolutionary history does make
some patterns of behavior unlikely
and rarely seen
✤
E.g., lactation is energetically
expensive and time-consuming,
and until very recently in human
history, was the only option for
feeding infant
✤
How does that affect the costs and
benefits of pursuing different
behaviors, such as foraging
activities?
Lecture 3
The Selfish Gene
01
Competition is the key concept in
evolution
✤
Natural selection works though competition
✤
Competition occurs at all levels: from the gene to societies
✤
Genes compete for locations on the chromosome
✤
Groups of genes (i.e. those that produce a certain trait or characteristic)
compete with other groups of genes (other traits)
✤
Collections of traits are bundled into complex organisms that compete
against other organisms
✤
Those genes that get copied into more individuals are those that persist
through time; they are favored by natural selection
What are genes competing for?
✤ The competition is for the resources required to reproduce,
including mates
✤ It is one’s conspecifics (others of the same species) that are most in
need of the same resources, and who are most likely to face the
same challenges (e.g. species-specific pathogens or parasites)
✤ The competition is relative, not absolute
✤ The characteristics or traits that allow one individual to obtain more
resources and produce more offspring than his/her conspecifics are
the characteristics that will become common in the population
Evolutionary competition
in a nutshell
Two men are sleeping in a campsite
when an angry bear crashes through
the bushes. They both leap up, but as
one starts running, the other pauses to
lace up his sneakers.
“Are you crazy?” yells the first guy.
“You’ll never outrun the bear if you
stop to do that!”
“I don’t have to outrun the bear,”
replies the second guy as he lopes
past the first. “I just have to outrun
YOU.”
01
Genetically selfish behaviors are
efficient
✤ Time and energy are finite resources; what is spent on one activity
cannot be spent on another
✦
For example, somatic energy expended healing injuries is energy that cannot be spent seeking
mates
✤ Genetically selfish behaviors are efficient, that is, they enable the
individual to reap the greatest benefits at the lowest cost
✤ Sometimes the most efficient behavior is to just take what you need,
trampling whoever is in the way
✤ Often, however, the costs or potential costs of such reckless behaviors
make them inefficient instead
Reproductive Strategies
✤ The behaviors designed to reproduce one’s genes into the next generation
are referred to collectively as “reproductive strategies”
✤ The various patterns of behaviors that are employed to get one’s genes
into the next generation are referred to as “reproductive strategies”
✤ In evolutionary terms, the term “strategies” need not imply a conscious
plan of action
✤
Age at maturation is part of a reproductive strategy, though it is not under conscious
control
✤ Strategies may be fixed (invariant) or facultative (dependent on features
of the local environment)
Strategies do not always
appear to be efficient
✤ Bloody battles and outrageous
adornment appear to be
inefficient strategies
✤ They require lots of energy
(which requires resources)
✤ They expose the individual to
risk, e.g. of predation
✤ They often seem not to serve
any purpose
01
1871: “The Descent of
Man, and Selection in
Relation to Sex”
✤
Darwin described a mechanism
distinct from “natural selection,” and
much more powerful: sexual
selection
✤
Can be used to explain extravagant
secondary sexual characteristics, esp
in males
✤ Identified two primary forms
✤ Intersexual selection (mate choice;
selection imposed by one sex on the
other)
✤
Intrasexual selection (competition
for mates; selection imposed by one
sex on others of the same sex)
Charles Darwin, 1874
01
Different kinds of selection
produce different kinds of
traits
✤ Intersexual selection (mate
choice) typically produces
adornments
Bright feathers, songs,
markings, etc.
✤ Intrasexual selection (direct
competition) typically produces
weapons
✤ QUESTION:
What kind of
selection do you think
produced human creativity? Is
it a weapon? Or an adornment?
Teeth, antlers, claws, large
body size, etc.
01
Genetic selfishness ≠ behavioral
selfishness
✤
In fact, genetically selfish behavior can actually appear to be
costly to the individual, while benefitting someone else
(altruistic)
✤
Reproductive success is measured at the level of the genes
✤
You share your genes with your kin
✤
“Degree of relatedness” (r) refers to the amount of genes in
common with a particular class of relative
–
For example, because you get half your genes from your mother and
half from your father, the degree of relatedness with a parent or
offspring is .5
Hamilton’s rule of kin selection
✤ If you benefit a relative, even at a cost to your own
reproduction, you will be benefitting some of your
genes (genes that also appear in your kin)
Hamilton’s Rule:
rb>c
relatedness*benefit to kin > cost to self
Individuals will incur greater
costs to benefit closer kin
✤ r = .5 for full sibs, parents
✤ r = .25 for half sibs
✤ r = .125 for first cousins
✤ The more distant the relative,
the higher the threshold for a
cost to be “worth it.”
✤ “I would give my life for 1
brother or 4 cousins” (J.S.
Haldane)
01
Behavioral ecology
✤ The goal of a behavioral ecology approach is to try to predict the kind
of behavior we are likely to see given a specific set of environmental
conditions
✤ “Environment” includes the subsistence ecology; predator/prey
ecology; social context; one’s own status (e.g. age); etc.
✤ Some factors in the environment change very slowly or not at all:
e.g.
gravity has functioned in the same way throughout evolutionary
history
✤ Some factors change very rapidly: e.g. a female’s fertility status changes
monthly or seasonally; testosterone levels change throughout the day
Environments of Evolutionary
Adaptedness (EEAs)
✤ The EEA is the environment for which a given trait
was selected
✤ A trait is in equilibrium if the current environment is
that for which the trait evolved; i.e. the trait is
functioning as it should
✤ A trait is in disequilibrium if the current environment
is different from that for which the trait evolved; i.e.
the trait is no longer adaptive
Behavioral ecology rests upon several
assumptions
✤ Organisms are typically well-suited to the environments in which they
live (the phenotypic gambit)
✤ The only mechanism for genes frequencies to change (i.e. for biological
adaptation to take place) is through reproduction or kin selection
✤ Organisms that are more efficient in getting resources in any
environment will survive and reproduce better than others
✤ Because we cannot observe genes directly, we rely on the “proximate
correlates” of reproductive success — e.g. resources, status — to
measure efficiency
Behavioral ecology rests upon several
assumptions (con’t)
✤ Organisms do not evolve adaptations to pursue the spread of genes
(which we cannot perceive), but to pursue the proximate correlates
of reproductive success (i.e. to pursue resources, status, sex, etc)
✤ Species in novel environments may find that the proximate
correlates are no longer appropriate; thus the phenotypic gambit
will be false (the behavior observed is not well-suited to the
environment even though it evolved through natural selection)
✤ Humans are not qualitatively different from other animals in terms
of what we “evolved” to do: i.e. obtain and use resources to spread
our genes into the next generation