WEEK 1
Lectures: February 6-8, 2007
*5 Major Questions:
1. What happened?
2. How do we figure out what happened?
3. Why are we the way we are?
4. How does evolution work?
5. Why is human evolution important?
--Humans are a good model for studying overall evolution b/c “nothing in biology makes
sense except in the light of evolution.”
*5 Theories of Evolution*
1. Evolution as such
2. Common Descent
3. Gradualism (i.e. evolution proceeds slowly and WITHOUT jumps)
4. Multiplication
5. Natural Selection
*Darwin: Evolution is descent with modification.
FITNESS: ability to reproduce and act
ADAPTATION: useful feature, shaped by natural selection that PROMOTES
SURVIVAL.
HUNTER-GATHERERS:
--They hunted a lot more than they gathered, and inversely, chimpanzees gathered a lot
more than they hunted.
--H-Gs are COMPLETELY dependent upon tools!
--Most food is cooked or processed by H-Gs.
-H-Gs and aggression: Lethal violence and non-lethal violence are VERY low, the latter
particularly staggeringly low compared to similar rates for chimps.
Reading: B&S 1-3
CHAPTER I: Adaptation by Natural Selection
*adaptations: exquisitely constructed components that interact to help the organism
survive and reproduce.
CONSTRUCTION serves FUNCTION.
I.
Darwin
a. (1800s) Most people did not believe his Theory of Adaptation because
they believed that adaptations were the result of divine creation.
b. Henslow = the professor who encouraged Darwin to travel aboard the
HMS Beagle and map the nature found on the coast of South America.
c. Darwin’s 3 Postulates
i. The ability of a population to expand is infinite, but the ability of
any environment to support populations is always finite.
ii. Organisms within populations vary, and this variation affects the
ability of individuals to survive and reproduce.
iii. The variations are transmitted from parents to offspring.
*Darwin’s “Natural Selection”: Traits that confer advantages in survival and
reproduction are retained in the population, and traits that are disadvantageous disappear.
iv. Darwin’s finches
v. Grants and the island of Daphne Major on which they were able to
study how much the drought effected the finches’ beak depths;
through Natural selection, the morphology changed so as to make
the finches better adapted.
vi. Evolutionary Theory: Phenotypes (i.e. finch beaks) will continue to
deepen until the cost of larger-than-average beak size exceeds the
benefits.
1. Even if phenotypes are not changing, natural selection is
still occurring. In fact, populations do not remain static
unless natural selection is operating!
2. Adaptation: comes from competition among individuals,
and not between entire populations or species!!
a. Natural selection can help the individual but harm
the overall species group.
b. Continuous variation (slow, steady, and constant
with intermediate stages of characteristics) vs.
Discontinuous variation (i.e. mutations)
c. Small, random variations of natural selection lead to
complex adaptations.
d. Convergence: the evolution of similar adaptations
in unrelated groups of animals.
*We don’t always have fossil records proving jumps in evolutionary patterns, but that’s
probably because our fossil record is quite sparse!!
*Jenkin’s Argument: Blending inheritance there’s little or no variation available for
selection to act on. (And as one of Darwin’s three necessary postulates, variation remains
essential to natural selection!)
HOWEVER, genetics account for much inheritance and NOT blending!!
CHAPTER II: Genetics
I.
Mendel!
a. Variants: forms of traits
b. Crosses: matings between plants
c. Fo generation, F1 generation, F2 generation, etc.
d. 2 of Mendel’s conclusions:
i. Genes are inherited from both the mother and father
ii. Both the mother’s particles and the father’s particles are equally
likely to be transmitted. Therefore, it’s an INDEPENDENT
ASSORTMENT!
II.
Mendel is no longer refuted when in 1900, after 40 years of being ignored,
scientific understanding of the role of chromosomes in the formation of
gametes reinvigorate the believability of Mendel’s theory (recall, Mendel only
observed plants and therefore dealt with just phenotypes and no genes).
III.
IV.
V.
Mitosis—normal cell division; Miosis—sexual cell division that produces
gametes
GENES are carried on chromosomes!!! (Refresh yourself on the splitting of
chromosomes!) All the genes carried on all the chromosomes are referred to
as the genome.
There is a lot of detailed information in this section. I read it all, and it
doesn’t seem to pertain much to the information covered in lectures. So feel
free to skim it (if you haven’t already done so), but chapters I and III are
more pertinent.
CHAPTER III: The Modern Synthesis
I.
Phenotypes vs. Genotypes
a. Population Genetics: What happens to genes in populations that are
undergoing natural selection
b. GENOTYPIC FREQUENCY: one should always track the frequencies
of the genotypes rather than the number of individuals with each genotype
because the former is independent of the local population size, whereas the
latter is not!!
i. Goal of Evolutionary Theory: HOW do genetic frequencies change
over time?
1. 4 processes that alter the frequencies of genes and
genotypes:
a. Sexual reproduction
b. Natural selection
c. Mutation
d. Genetic drift
2. Sexual Reproduction
a. Random mating among humans is similar to the
random union of gametes!!
b. Weinberg equilibrium: The realization that sexual
reproduction alone does not alter phenotypic and
genotypic frequencies was the key to understanding
how variation is maintained!!
**Although sexual reproduction and random mating alone cannot lead to evolution
over time, natural selection can produce changes in the frequencies of alleles!!!**
MODERN SYNTHESIS: using Mendelian genetics to explain continuous variation.
*There are no blending of genes during sexual reproduction. Even if offspring appear to
be a blended/intermediate between their parents, sexual production actually produces NO
blending in the genes themselves!
* “Hidden Variation” = “hidden” genotypes are present even when phenotypes evolve to
that which is of “higher fitness.” Therefore, variation and mutation are protected from
selection. (And that’s good since Mutation add variation to a population by continuously
introducing new alleles…thereby fulfilling one of Darwin’s three requirements for
evolution.)
*Behavior plasticity vs. behavior canalization (i.e. showing the same phenotype in a wide
range of environments)
*Genetic drift: particularly common among small sampling populations. More rapid
change in small populations than in large ones. Also, because of genetic drift, isolated
populations become genetically different from one another over time.
Reading: Mayr 2001
--Not until the 1930s did scientists finally agree that evolution based on essentialism was
completely invalid.
*Darwin-Wallace Theory: Based on population rather than essentialism.
DARWIN’S EVOLUTIONARY MODEL OF NATURAL SELECTION:
1. Every population is so fertile that its size would increase exponentially if not
constrained.
2. Size of populations remain stable over time.
3. The resources available to every species are limited. There is an intense struggle for
survival among the members of that species.
4. No two individuals of a population are exactly the same; they differ in their
probability for survival (i.e. natural selection)
5. Many of the differences among individuals of a population are heritable. Therefore,
natural selection over many generations results in evolution.

“Owing to unequal survival and reproductive success of its
individuals, there is a continuing genetic turnover in each
population as a result of chance and natural selection.”
a. Even greater breaks in continuity occur where there
are geographical boundaries limiting dispersal.
b. “A local population is sometimes called a deme,
which may be defined as the community of
potentially interbreeding individuals at a given
locality.”
c. NATURAL SELECTION IS REALLY A
PROCESS OF ELIMINATION.
i. 2-step process:
1. everything leading up to the
production of the new zygote.
a. EVERYTHING left up to
chance.
2. Elimination: the “goodness” of the
individual is continually tested.
a. “Survival of the fittest.”
(Selection)
Reading: Marlowe, 2005
*Perhaps Hunter-gatherers (H-Gs) only appeared at the end of the last glaciaration.
*Our ancestors must have varied widely (and had varied technologies) in order to be able
to survive in such varied climates.
*The fact that a habitat is good for farming does not make it equally good for foraging
and vice versa.
*Women may use food from men merely to speed up their reproduction rate.
*Central place foraging is typical among most human foragers. = “central place
provisioners”
*Highly variable species!
*Technological Advances: “The bow was such a technological leap forward that it could
have led to an increase in meat consumption and population growth rates, eventually
reducing game populations in certain areas and hastening the adoption of agriculture.”
WEEK 2
Lecture: February 13, 2007
As primates, our evolutionary history was contingent on what happened in earlier
primate evolution. Primates provide key Comparative Data on relationships between
aspects of behavior, ecology, and anatomy relevant to humans.
PRIMATES as MAMMALS:
1. Evolutionary Context
2. Primate Diversity
3. Primate Adaptations
1. Evolutionary Context
a. Linnaen Taxonomic System
i. (Complex to basic) Domain->Kingdom->Phylum->Class->Order>Family->Genus->Species
ii. Hierarchical scheme of classification with species most basic unit
iii. Classification based on function (biologically arbitrary)
iv. Classification should reflect evolution
b. Evolution is change over time, therefore novelties (features that have
changed) provide evolutionary information.
i. Closely-related organisms share novelties derived from a common
ancestor (homologies)
c. Key distinction: Clade-share same common ancestor (better for evaluating
evolutionary relationships) vs. Grade-similar level of organization
2. Primate diversity
a. Prosimians(Before Apes)
b. Strepsirhines
1. Very “primitive” primates.
2. No wall (septum) behind orbit
3. Reduced upper incisors
4. Grooming claw
5. Tooth Comb
6. Nails & Claws
 Differences between Anthropoids (Monkeys) and Prosimians:
Anthropoids have fused frontal lobe, fused manibular symphysis,
postorbital closure, larger brain¸ lacrimal bone in orbit, nails
ii. Anthropoids (Monkeys)
1. New World Monkeys (Platyrrhines)
a. 100 g-10 kg, Broad, flat external nose, Very
diversive, 2 1 3 3, Underwent adaptive radiation,
arrived in S. America 30 mil yrs ago
2. Old World Monkeys
a. Two subfamilies
i. Colobines-Leaf Eaters
ii. Cercopithecines-omnivores
-Both subfamilies very SPECIOSE
-Similarity between baboons and mandrills occurs namely
because of CONVERGENCE- which is an expected
outcome of natural selection
-Difference between Old World Monkeys and Apes
(Hominoids)- Apes have narrow nose, narrow palete, while
apes have a larger brain, single molars, long arms
3. Apes
a. Less Apes: Gibbons, Saimangs
b. Great Apes: rangutans, gorillas, chimpanzees,
humans
c. Primate Adaptations
1. KEY POINT: Primates are generalized arboreal, tropical
mammals, and the niche: species context within an
ecosystem
2. Primates are exclusively tropical, except some macaques
a. Habitat-Forest, Gallery Forest, Woodland, Savanna
b. Diet-As generalists, primates tend to be omnivors
i. Body Mass/BMR: direct relationship
ii. Diet-> Log Matt. Rate vs Log Body Mass->
Higher animal higher rate of metaboli rate
iii. One possible explanation involves the
notion that bigger body has a longer
throughput time, and moer fermentation.
iv. Varied Diet requires generalized teeth
v. Inventory
1. Small, nutritious, hard to get,
binocular vision, manual dexterity
Small, Nocturnal, tough exoskeleton
2. Frugivory
 Seed dispersonrs, coevolution
with angiosperms
 Selectivity- Color sensitivity,
touch, manual dexterity
3. Folivory
 Problem=celluslose, foregut
fermentators, hindgut
germentat fermentators.
-Fruit Eaters: Long, small intestine, broad incisors
-Leaf Eaters: Enlarged long intestine
i.
ii.
iii.
iv.
Flesh, eggs, etc.
Another key adaptation for diet: vision,
a. Enclosed forward facing orbits
b. Stereoscopic vision
Olfaction thought to be less important.
a. But, how do we smell?
i. In test, humans performed just as well as dogs
tracking down chocolate and duck
ii. Humans have good sense of smell
Highly Tactile
a. Nails instead of claws, sensitive tactile pads
b. Good Climbers
i. Divergent big toes/thumbs, long, curved fingers,
long palms
1. gibbon, chimp, gorilla
c. Locomotion
i. Different habitats pose different locomotor
challengers
1. The higher metabolic rate, the more you
tend to weigh, and the more you weight
and have a higher metabolic weight, the
more terrestrial you are, while on the
other end, the less watts/grams the more
arboreal you will be.
ii. Most primates are quadrupeds
(arboreal/terrestrial)
1. Dog, Monkey
2. Have dorsal scapular, narrow thorax,
mobile hips, powerful elbow, bowed
radius, mobile shoulder, plantigrade feet,
bowed radius
iii. Some are suspensory
1. High shoulder, flexible hip, long arm
and wide forearm, long, curved fingers,
flexible wrist (Gibbon and orangutan)
iv. Knuckle-walking
v. How to be terrestrial and suspensory arboreal
and BIPEDALISM
a. Has traces of quadrupedal
adaptation, suspensory
adaptations, and knuckle-walking
adaptations
d. Size (and its consequences)
i. Body size has other consequences/effects
1. Specifically, life history
2. Larger BMR, body mass, metabolic rate:
More open, long lived , slow matures KSelected
3. Smaller BMR, body mass, metabolic
rate: Cryptic, short-lived, fast maturers,
r-selected
e. Sociality & Cognition
i. Primate brains-highest on graph of Log Body
Mass versus Log Brain Mass
ii. Chimp(50 kg animal): 350-400 cc
iii. Human (70 kg animal) :1300-1400 cc
iv. Expansion is primarily in neocortoex (occibital
lobe, gyri, sulci)
v. Primates are smart as a result of namely
COMPLEX SOCIAL GROUPS rather than diet,
predation
vi. Larger groups: Mostly diurnal anthropoids
1. Most prosimians: Small, nocturnal,
solitary
2. Monkeys, apes, etc.: Larger diurnal
groups
vii. Individuals live in groups because:
1. Potential fitness costs:
a. Increased visibility to predators,
Intragroup competition for food
2. Potential fitness benefits:
a. Protection from predators,
improved access to food
(intragroup competition), access
to mates, assistance in caring for
offspring
b. But, intragroup competition for
food and improved access to
food (intragroup competition) are
VERY habitat specific
viii. Habitats differ in resource distribution
1. High vs. Low Density
2. Small vs. Large Patches
3. Also, resource distribution matters most
for females, and female distribution
matters a lot for males
4. Keystone resources and fallback foods
are also important to the existence of
species and available resources
5. Consequences of group life Complex
social hierarchy, interactions, intrasex
competition
ix. Social intelligence
1. Brains are expensive; probably why
more social animals don’t have big
brains
x. Another consequence of group life:
1. Intrasex competition
a. Polygynous dimorphic canines
b. Monagamous monomorphic
canines
f. Conclusion
i. Human specializations are largely contingent on being primates
1. Specifically, humans are:
a. Smart
b. Visual and tactile
c. Generalists
i. Diet (high quality foods and omnivores)
ii. Specific locomotion
2. Humans are often unique and specialized in that:
a. We are large bodied, but don’t eat low quality food
b. We have large social groups, but not large canines
 Primates are territorial and defend high quality
resources and monitor the environment
Lecture: February 15, 2007
1. Evolutionary relationships between humans and apes (ancestors)
2. Comparative methods (behavioral reconstruction of fossils)
3. Contrast with humans ( last common ancestry)
1. Evolutionary Relationships
a. Monophyletic groups: descendants share a common ancestor
i.
Why important
b. History: Darwin and Huxley believed humans more closely related to
African apes: chimps and gorillas
c. Realtionships very crude in early 20th century (purely paleontological
view)
d. 1950s-1960s: surprising genetic data
i.
Quantitaive comparisons of proteins generated pairwise patterns of
similarity/difference
ii.
Genetic data can be arranged in many different ways to form
matrices, and there is one matrix which is a 'best fit' where row
entries are very similar
e. 3 surprises
i.
Humans closest to African apes = trichotomy
ii.
Protein change = molecular clock
iii. Relationships can be calibrated and measured
f. Perhaps most surprising result: genetic differences not equal to phenotypic
differences
g. Humans are behaviorally and morphologically different from African apes
but genetically similar
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Genetic and phenotypic change are "uncoupled"
b/c most DNA not under selective pressure, it acquires and maintains random
mutations over time at a certain ratea and can be used judiciously as a "clock"
Phenotypic change is non-constant and cannot be used as a clock
2. Comparative method
a. Comparison of species in phylogenetic context to test/infer relationships
between variables
i.
Relationship between diet and tooth size and structure
ii.
Frugivores have larger brains and smaller guts than leaf-eaters
b. Key point: such correlations are only 'patterns of association'
i.
A and B usually correlated in living species
ii.
Therefore, if a fossil exhibits A, then we can expect B
iii. Correlation is not causation
c. Key ape characteristics
i.
Tropical
ii.
Forest
iii. Fruit-eaters
iv.
Arboreal
v.
Variably social
vi.
Smart
d. What are critical factors necessary for survival and reproduction
i.
Food
1. In patches, size has important effect in feeding strategy
ii.
Safety
1. How to avoid predators/aggression - interspecific: be
social, choose resting place carefully
2. Intraspecific:be social and use strategies for sex/age/rank
iii. Mates
1. Reproduction requires investment of time/energy, sexes
differ
a. Females are ecological sex b/c limited by resources
available
e. Primate social groups: one sex tends to migrate
f. 2 species of chimp: common chimp (allopatric) and pygmy/bonobo
(synpatric)
g. Chimps live in tropical forest, prefer fruit
i.
Fallback foods very important b/c of effects on behavior and
morphology
ii.
Both arboreal and terrestrial
iii. Trees important for feeding, resting, avoiding predators
iv.
Males and females dimorphic by about 30%
v.
Social groups or 'communities' vary in size: 20-100 malesl and
females
1. Males stay in natal group: more social, related, defend
territory: more social, more related
2. Females migrate when mature: less social, less related
vi.
Hierarchical and status-seekers
1. Male cominance based on aggression
2. Males dominant over females - contest competition
a. Scramble competition
vii.
Little food sharing
1. Occasionally tolerate scrounging
viii. Meat: minor but highly prized part of diet
1. Dominant male usually determines distribution - unlike
human meat sharing
ix. Tool-makers
x. Reproduction and life history
1. Matings are promiscuous, dominant male sires most of new
offspring, consortships occasionally form, infanticide
sometimes a problem
xi. Life history: summary of…
xii. Bonobos have more slender bones: legs longer relative to arms,
smaller heads
h. Gorillas: lowland western, mountainous eastern
i.
Big and dimorphic
ii.
Preferred food: ripe fruit, fallback: pith and leaves
iii. Upright climbers, suspensors when young, mostly knuckle walkers
like chimps
iv.
Live in groups with single male or at most two adult males plus
females and offspring, females leave natal groups to join male
groups
1. Surplus male adults - intermale fights, group take-overs,
frequent infanticide
v.
Reproduction: gorillas reproduce faster than chimps, females first
reproduce about 10 years vs 13-15 in chimps, interbirth interval is
about 4 years vs. 5.5 in chimps, lifespan less
vi.
Morphologically like chimps but bigger, how?
1. African forests continually expanding and contracting
creating isolated zones - areas where you can get allopatric
speciation - fate of such isolation is to go extinct or evolve
2. If forest isolate = fruit poor, one solution is to get bigger to
cope with lower quality food
Many changes in shape scale with changes in size
African apes are larger and smaller versions of the same animal
Last common ancestor between gorillas and chimps must have been chimp-like, as well
as between humans and chimps
Reading: B&S, Chapter 5
Introduction to the Primates
Primates are Our Closest Relatives

The fact that humans and other primates share many characteristics
means that other primates provided valuable insights about early
humans

Humans are more closely related to nonhuman primates than we are to any
other animal species

Anatomical similarities among monkeys, apes, and humans led Swedish
naturalists Carolus Linnaeus to place humans in the order Primates in the
first scientific taxonomy, Systema Naturae (1735)

Humans were later placed in their own order because of out distinctive
mental capacities and upright posture.

We share many aspects of morphology, physiology, and development with
primates. I.e. Visual Abilities and Grasping Hands and Feet

Also, share an extended period of juvenile development and rimates as a
whole have larger brains in relation to body size than members of most
other taxonomic groups

Homologies in behavior as well b/c of physiological and cognitive
structures that underlie human behavior are more similar to those of other
primates than to members of other taxonomic groups

Nonhuman primates, therefore provide useful models for understanding
the evolutionary roots of human morphology and the origins of human
nature.
Primates Are a Diverse Order

Diversity within the primate order helps us to understand how
natural selection shapes behavior

There is great morphological, ecological, and behavioral diversity among
species within the primate order

Primates range in size from tiny mouse lemor (30 grams) to male gorillas
weighing (350 lbs)

Some species live in dense tropical forests, others in woodlands and
savannas
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Some eat only leaves, other on an omnivorous diet, including fruits,
leaves, seeds, gum, nectar, insects, small animal prey
Some are solitary, other gregarious
Some nocturnal, others diurnal
Some actively defend their territory from intruders, others don’t
Some have only females that provide care, others have males help out
Evidence of diversity among closely related organisms living under
different ecological conditions helps scientists understand how
evolution shapes behavior.
Animals that are closely related to one another phylogentically tend to
be very similar in morphology, physiology, and life behavior.
So, differences among organisms indicate adaptive responses to specific
ecological conditions and similarities among more distantly related
creatures living under similar ecological conditions are likely to be
product of convergence.
Sexual Dimorphism- the observation that there are substantial differences
in male and female body size-suggests that highly dimorphic hominids in
the past were not monogamous.
Features that Define the Primates
The primate order is generally defined by a number of shared, derived characters,
but not all primates share all of these traits.
 Animals in primate order typically similar: thick coat of hair, four limbs, five
fingers, but share these with all mammals.
 So define in terms of DERIVED FEATURES
 Definition of Primate Order:
 Big toe on foot is opposable and hands are prehensile, so
primates can use their feet and hands for grasping. Opposable
big toe has been lost in humans
 There are flat nails on the hands and feet in most species,
instead of claws, and there are sensitive tactile pads with
fingerprints on fingers and toes
 Locomotion is hind limb dominated, meaning the hind limbs
do most of the work and the center of gravity is nearer the hind
limbs than the forelimbs.
 There is an unspecialized olfactory (smelling) apparatus that is
reduced in diurnal primates
 The visual sense is highly developed, the eyes are large and
moved forward in the head, providing stereoscopic vision
 Females have small litters, and gestation and juvenile periods
are longer than in other mammals of similar size
 The brain is large compared with the brains of similarly sized
mammals, and it has a number of unique anatomical features
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The molars are relatively unspecialized, and there is a
maximum of two incisors, one canine, three premolars, and
three molars on each half of the upper and lower jaw
 There are a number of other subtle anatomical characteristics
that are useful to systematists but are hard to interpret
functionally
Many primate species can perceive color and their eyes are set forward in the
head, providing them with binocular, stereoscopic vision.
 Binocular vision means that their fields of vision of the
two eyes overlap so that both eyes perceive the same
image
 Stereoscopic vision means that each eye sends a signal
of the visual image to both hemispheres in the brain to
create an image with depth.
 Trends are not uniformly expressed within
primate order, some play more important roles
in prosimian primates than in anthropoid
primates
Prosimians include lorises and lemurs, and the anthropoid primates include
monkeys and apes
Primates as a group have longer pregnancies, mature at later ages, live longer
and have larger brains than other animals of similar body size do. These
features reflect a progressive trend toward increased dependence on complex
behavior, learning and behavioral flexibility within the primate order
 “Intelligence as a way of life”
Teeth play a very important role in lives of primates: allows primates to
process food and use as conflict when facing other animals.
Primatologits use tooth wear to gauge age of individuals, and use features of
teeth to assess the phylogenetic relationships among species.
Paleontologists rely on teeth to identify and make inferences about the
developmental patterns, dietary preferences, and social structure.
1) None of these traits makes primates unique (ie. Dolphins)
2)Not every primate possess all of these traits
Primate Biogeography
Primates are generally restricted to tropical regions of the world

The continents of Asia, Africa, and South America and the islands that lie near
their coasts are home to most of the world’s primates.
 Primates are mainly found in tropical regions of the world where fluctuations
from day to night greatly exceed fluctuations in temperature over the course of the
year.
A Taxonomy of Living Primates
Primates are divided into two groups: the prosimians and the anthropoids
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Many of the primates Prosimii are nocturnal and have adaptiations to living in
darkness including a well-developed sense of smell, large eyes, and independently
movable ears.
By contrast, monkeys and apes who make up Anthropoidea evolved adaptations
more suited to a diurnal lifestyle. In Anthropoidea, traits related to increased
complexity of behavior are most fully developed
Classification of primates into prosimians and anthropoids does not strictly reflect
the patterns of genetic relationships among the animals in the suborders.
Infraorder-taxonomic level immediately below suborder
More traditional division into prosimians and anthropoids is an example of
evolutionary taxonomiy in which overall similarity and relatedness are used to
classify species.
The Prosimians
The Prosimians are divided into three infraorders: Lemuriformes, Lorisformes,
and larsiiformes
 Lemuriformes include lemurs and underwent adaptive raditation because
faced with a diverse set of available ecological niches
 Quadrupedal , arboreal, travel by jumping in a n upright posture from one tree
to another known as vertical clinging and leaping
 Some lemurs are nocturnal, some are diurnal
 Female lemurs control male lemurs, dominant.
 Lorisiformes comprises small, nocturnal, arboreal residents of the forest of
Asia and Africa. Galagos are active and agile, leaping through trees and
lorises move with deliberation (have adaptation of with specialized network of
blood vessels that allows them to remain immobile for long periods of time)
 Tarsiiformes includes tarsiers which are enigmatic primates who live in the
rain forests of Bronea and the Phillipines.
 Tarisers are small, nocturnal, and arboreal and move by vertical clinging and
leaping.
 Tarsiers are only primates who rely exclusively on animal matter, deeding on
sects and small vertrbrate prey.
The Anthropoids
The suborder Anthropoidea contains the infraorders Platyhrrhini and Catarrhini
 Platyrrhini-New World monkeys
 Catarrhini- Old World Monkeys and Apes
The infraorder Platyrrhini (New World Monkeys) is divided into two families:
Callitrichidae and Cebidae
 New World monkeys encompass considerable diversity in size, diet, and
social organization, but they do share some basic features. All except aotus are
diurnal, all live in forested areas, and all are mainly arboreal.
 Most new world monkeys are quadrupedal, moving along the tops of branches
and jumping between adkacent trees. Some species of Cebidae can suspend
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themselves by their hands, feet, or tail and can move by swinging by their
arms beneath branches.
Family Callitrichidae is composed of marsomets and tamarins.
They are extremely small, largest weighing less than 1 kg, they have claws
instead of nails, only 2 molars, while all monkeys have three and frequently
give birth to twins, and sometimes triplets
Polyandry
Cebid monkeys are generally larger than marmosets and tamarins .Family
cebidae is divided into six subfamilies that encompass considerable diversity
in social organization, deeding behavior, and ecology. The subfamiliy
Aloutatinae is composed of several species of howlers
Subfamily Callimiconinae is compsed of just one species, Goeldi’s monkey.
Apotinae and Callimiconinae monkeys are small bodied fruit eaters and live
in monogamous groups.
The infraorder Catarrhini contains the monkeyts and apes of the Old World and
HUMANS
 Cattarhine primates share number of anatomical and behavioral features that
distinguish them from the New World Primates.
 Most Old world monkeys and apes have narrow nostrils that face down, while
New World Monkey have round nostrils.
 Old World Monkeys have two premolars on each side of the upper and lower
jaws, New World monkeys have 2 premolars on each side of the upper and
lower jaws, New World Monkeys have 3. Most Old Wolrd Primates are larger
than most new world species, and old world monkeys and apes occupy a
wider range of habitats than new world species do.
 Catarrhine primates are divided into two superfamilies:Cercopithecoidea (Old
World Monkeys) and Hominoidea (Apes and Humans)
o The Superfamily Cercopithecoidea encompasses great diversity in
social organization, ecological specializations, and biogeography
 Colobine monkeys are found in forests of Africa and Asia and
are perhaps the most elegant of the primates
 Slender bodies, long tails, and often beautifully colored coats
 Colobines are mainly lead and seed eaters, and spend most of
time in trees
 Also, have complex stomachs which allows them to maintain
bacterial colonies that facilitate the digestion of cellulose
 Colobines are often found in groups composed of one adult
male and an umber of adult females
 Cercopithecine monkeys are found in Africa and more variable
in size and diet than the colobines are. The cercopithecines
consist of baboons, macaques, and ververts (just a few)
 Typically remain in their natal groups, groups where they were
born
o The superfamily Hominoidea includes three families of apes:
Hylobatidae (gibbons), Pongidae(oranguatans, and chimpanzees_
and Hominade (HUMANS)
 Hominoids differ from cercopithecoids in a number of ways.
Most readily observed difference b/t apes and monkeys is that
apes lack tails.
 Apes share some derived traits, including broader noses,
broader palates, larger brains…
 But they retain some primitive traits, such as relatively
unspecialized molars
 Old world monkeys: the prominent anterior and posterior cusps
are arranged to form 2 parallel ridges.
 Apes: five cusps on lower molars are arranged to form a side
turned Y shaped pattern of ridges
 Hylobatidae includes lesser apes (gibbons and siamangs) and
living members are now found in Asia
 Family pongidae includes larger bodied great apes (orangutans,
gorillas, baboons, and chimpanzees)
 Orangutans are found in Asia, while chimpanzees, bonobos,
and gorillas are restricted to Africa
 Humans in own family, *Hominade* but many taxonomists
believe humans belong with other great apes in Pongidae
 Lesser apes are slightly built creatures with extremely long
arms in relation to their body size
 Gibbons and siamangs are strictly arboreal and they use thei
long arms to perform acrobatic feats
 Gibbons and siamangs are the only true brachiators (propel
themselves b their arms alone in free flight between handholds)
 All of lesser apes live in monogamous family groups,
vigorously defend their home ranges, and feed on fruit, leaves,
flowers, and insects
 Orangutans are among the largest and most solitary species of
primates and feed primarily on fruit, leaves and bark
 Gorillas, largest of apes are in isolation and live in small
groups that contain one or two adult males and a number of
adult females and their young. Eat a lot of plants and bamboo,
and eat little fruit because fruiting plants are scare in their
mountainous habitats
 Adult male mountain gorillas called silverbacks play a central
role in structure and cohesion of their social groups.
 Males sometimes remain in their natal groups to breed, but
most males leave their natal groups an acquire females by
drawing them away from other males during intergroup
encounters.
 Humankinds closest living relatives are chimpanzees
 Play an important role in study of human evolution.
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Observations about chimps to be important bases for
hypotheses about behavior of early humans
Bonobos are less well studied because they live in
inaccessible areas
Chimps and Bonobos form large multimale,
multifemale communities
Female chimps normally disperse from their natal
groups when they reach sexual maturity, while males
remain in their natal groups throughout maturity
Chimp communities are rarely found together in a
unified group
o Split up into smaller parties that vary in size and
composition from day to day
In chimps, the strongest social bonds among adults are
formed among males, while bonobo females form
stronger bonds with one another and with their adult
sons than males do
Chimpanzees modify natural objects for use as tools in
the wild
Primate Conservation
Many species of primates are endangered by 1) habitat destruction, 2) hunting, or 3)
live capture for trade and export
 Nearly 100% of primate species are considered to be endangered or critically
endangered, or are in real danger of extinction
 Efforts to save endangered primate populations have met with some success.
Reading: B&S, Chapter 10
Evolution of the first mammals
 Apes came from shrew-like ancestor
 Important to understand geological climate and biological conditions under which
evolutionary changes took place to understand why unique human traits were
favored by selection
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On major environmental change is the shifting of the continents (continental drift)
- important for two reasons
o Oceans serve as barriers between species
o Position of continents affects climate
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Much of our knowledge of evolutionary history comes from the fossil record
Radiometric methods for estimating the age of fossils
o Potassium-argon dating: used to date volcanic rocks, potassium decays
into argon at a known rate
o Carbon-14 dating: carbon 14 decays into carbon 12 at a constant rate
(measure ratio)
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Thermoluminescence dating: (they better not test us on this)
Electorn-spin-resonance dating - used to determine age of apatite crystals
in material like tooth enamel
Absolute radiometric dating supplemented by relative dating method based on
magnetic reversals of the earth's poles and other fossils
One of driving evolutionary forces was the evolution of flowering plants, which
created a new set of ecological niches. Primates evolved to fill these niches.
o Angiosperms and gymnosperms
Ancestors of modern primates were small-bodied nocturnal quadrupeds like a
modern shrew
Discovery of C. simpsoni with an opposable big toe with a flat nail, helps explain
why natural selection favored the basic features of primate morphology
o Likely that evolution of grasping hands and feet precede the movement of
the eyes to the front of the face
We see first modern features in the Eocene epoch which was warm and wet, like
tropical rainforests
Primates then radiated during the Oligocene, swampy forest
Primates appear in South America for first time in Oligocene, but unclear how
they got there
Miocene period was warm and moist, then became cold and dry.
First evidence of adaptations for suspensory locomotion comes from Miocene
fossils
Apes and monkeys differ in some features of their skeletal anatomy, dentition,
brain size and life history patterns
Middle Miocene saw a new radiation of hominids and the expansion of hominoids
throughout much of Eurasia
No clear candidates for the ancestors of humans or any modern apes, except
perhaps orangutans
Ape species abundant during middle Miocene, monkeys were not. Many ape
species became extinct and replaced by monkeys during the late Miocene and
early Pliocene
Reading: Wrangham (African apes as time machines)
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Evolution from chimp-like common ancestor
Based on cranial ontogeny, ancestor more chimp-like
Implications for behavior
Relevant relationship in phenotype and morphological evolution
Morphological evolution not always correlated with molecular clock
Reduction in aggression leads to reduction in sex dimorphisms and juvenile
features in bonobos
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Lethal raiding began 6 mya
Concealed ovulation 1.9 mya
Reading: Ruvolo (Hominoid genetic diversity)
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Why compare humans to primates?
Human genetic diversity – no races or subspecies
Subspecies exist within primate species
Look at mitochondrial DNA because it’s maternally inherited and evolves faster
Genetic diversity within humans and how it arose – molecular clock
o Gene flow after isoloation
o Common ancestry – not enough time to develop differences
The evidence supports the second option above
Human origin
o Homo erectus – out of Africa hypothesis
o Hybridizatioin between h. erectus and h. sapiens
Human morphological differences younger than genetic differences
In orangutans, genetic differences are not all mirrored in morphological
differences
Medical relevance: genetic variation and populations, organ transplants, drug
design, nonhuman hominoids as human surrogates
WEEK 3
Lecture: February 20, 2007
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in spring of 1994, still a debate about whether humans were more closely related
to chimps or apes
then a part of the mandibular corpus (jawbone) found in Lothagam by Mary
Leakey, dated to 5.5 mya
Ardipithecus ramidus found in Dec. 1994 in Ethiopia (4.4mya)
Biological Species Concept (BSC) – a set of actually or potentially interbreeding
organisms (Most common definition of a species)
Problems with BSC
 Hybridization – i.e. horse and donkey making a mule
 Morphological (form) differences don’t necessarily = genetic differences
 Applying it to fossils
Phylogenetic Species Concept (PSC) – group of organisms who share a single
common ancestor; diagnosable by unique combination of species
 Apomorphies – unique derived features
Problems with PSC
 Smallest group with unique features?
 Which characters to use?
 Diff. genes can have diff. evolutionary histories
Evolutionary Species Concept (ESC) - a lineage evolving separately from others
with its own evolutionary histories and tendencies
Problems with ESC
 Need a good fossil record (currently lacking)
 Somewhat arbitrary
What is a genus?
 Monophyletic – shares an exclusive common ancestor
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 Adaptively similar
E. African Rift System – place where 2 plates are pulling apart, good place to find
fossils
A. ramidus primarily defined by its teeth (similar to Pan, but thicker enamel)
 Foramen magnum (brainstem hole) positioned anteriorly (forward) –
possibly a biped?
 Arboreal, arms not necessarily weight bearing (points to biped)
A. ramidus kadabba subspecies found, roughly 5.2-5.5 mya
 Kadabba like A. ramidus, thick teeth, small canines, high shoulders, thick
teeth
Subspecies – geographic subdivision of a species
Ardipithecus shows early hominids chimp like, had thick teeth, possibly bipedal
Orrorin tugenensis (6mya) found in Kenya
 Chimp-like teeth, thick enamel (???), deep mandibular corpus
 Femoral anatomy leads to conclusion that orrorin may have been a biped
 in a woodland near a lake possibly
Sahelanthropus tchadensis found in Chad (6 – 7.5 mya)
 Chimp-like incisors, smaller canines, bigger and thicker cheek teeth
 Large browridge, vertical face, short snout
 Brain about the size of a chimps (after virtual reconstruction)
Relationship between foramen magnum (brainstem hole) and orbital plane (where
eyes face) can lend evidence for bipedalism
 Sahelanthropus’ foramen magnum more centrally located, may have been
a biped
 Facial similarities to humans
Sahelanthropus raises questions about
 What else is missing
 Its relationship to other hominids
 Habitat
 What type of biped it was
 Changes in chimpanzees
Bipedalism may be the distinguishing factor between chimps and humans
Lecture: February 27, 2007
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australopithecine radiation 4-2 mya
austs may have been an intermediate stage or an ancestor in human evolution
wide radiation, diverse adaptations, abundant fossil evidence
Taung baby found by Raymond Dart in S. Africa, foramen magnum (FM) looks
like a biped
Robert Broom – started excavating Sterkfontein - a limestone cave – formed by
water seeping in, causing collapses and creating limestone casts around bones
 leopards would bring the kills to the caves – many of which were
australopithecines
 a large amount of early hominid fossils came from there
Mary & Louis Leakey – digging in Olduvai Gorge and found another
australopithecine in 1959
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 Laetoli footprints found in 1978
Lucy found by Don Johanson, important because it was relatively intact skeleton
Species info –
 Sites, major fossils, discovery
 Age, ecological context
 Anatomy – cranial, dental, postcranial, body size / dimorphism (how
different the male and female body sizes are)
 Behavior – diet, locomotion, cognition, etc.
Species name: genus + trivial name, both italicized (i.e. Homo sapiens)
Rules of precedence - whoever gets to the species first gets to name the species,
and if a species is named but turns out not to be a species then that name can
never be used again (nomen nutum)
Type specimen (holotype) – the one fossil specimen that all new specimens must
be compared to (no type specimen for homo sapiens)
2 types of australopithecines – gracile and robust
Gracile As
 A. anamensis – 3.9-4.2 mya, E. Africa
 A. afarensis – 3-3.7 mya, E. Africa
 A. africanus – 2-3mya, S. Africa
 A. garhi – 2.5mya, E. Africa
 A. bahrelghazali – 3.5 mya, C. Africa
Robust As
 A. aethiopicus – 2.6mya, E. Africa
 A. boisei – 1.5-2 mya, E. Africa
 A. robustus – 1.5-2 mya, S. Africa
 K. platyops – 3.5 mya, E. Africa
Ontogeny (development and formation throughout life) issues –
 Humans develop at a slower rate than other primates
 Takes longer for humans to develop all of teeth
 People used to think that As progressed like humans, but more likely that
they developed at stages like chimps
Reading: B&S, Ch 6
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2 major concerns of primates in the wild – eating and not being eaten
Energy an animal requires based on
 Basal metabolic rate – how much energy an organism uses while at rest
 Active metabolism - how much energy used when active
 Growth rate
 Reproductive effort
Primates require the correct amount of water, amino acids (to make protein), fats,
carbs, vitamins, and minerals
Primates must avoid toxins – most plants create secondary compounds that
prevent them from being eaten
All primates have 1 primary protein source and 1 primary carb source
Each primate depends more on one food type than another – names for them:
 Frugivore – depends on fruit
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 Folivore – leaves
 Insectivore – insects
 Gummivore – plant gum
Insectivores bigger than folivores who are bigger than frugivores
Fruits can be hard to find in rainforests because of short ripening time, few of one
type of tree
Diurnal – active during the day, nocturnal – at night, cathemeral – both
Primates probably evolved from a nocturnal ancestor
Territorial primates defend territory and keep other males out, nonterritorial
primates’ home ranges may overlap but encounters may be violent
Territoriality stems from resource protection and mate defense
Some primates have calls to alert others about predators, some primates of
different species join together and keep watch for different types of predators
Sociality is common in primates but not common in mammals
Costs and benefits to socialization – better protection vs. competition for
resources and mates
Still some debate as to primary reason why primates form social groups –
protection v. resources
Scramble competition – when resources are distributed evenly across the
landscape (ex. candy on the ground after busting a piñata)
Contest competition – when resources are limited and can be monopolized
profitably (ex. musical chairs)
Dominance relationship – when a certain type of individual wins almost all the
time
Female philopatry – the incentive to stay with one’s kin
Domination less important when between-group competition is stronger than
within-group competition
Social organization evolution may be difficult to change
Inbreeding reduces viability of offspring, so males and females leave natal groups
when reaching sexual maturity
Reading: B&S p269-73
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Miocene temperature drop caused primates to have to deal with changing African
environment
Hominins began appearing in fossil record 6mya, walked upright and ate new
kinds of food, no longer just tree dwellers
5 factors distinguishing humans from apes
o Walk bipedally
o Dentition / jaw musculature is different
o Larger brains in relation to body size
o Develop slowly – long juvenile period
o Elaborate and symbolic culture transmitted thru spoken language
Ardipithecus, Orrorin, and Sahelanthropus discussed (see lecture notes for more
details)
o Earliest fossils similar to humans
Reading: Swartz, Biomechanics of Primate Limbs
Anatomy of the primate postcranium important
- force can cause bones to deform and (with enough force) break
- (much of this reading is superfluous and covered in lecture)
WEEK 4
Lecture: February 27, 2007
DATES AND PLACES:
(1925) “Taung Baby” in South African limestone quarry; ancestor of humans
(1959) “The Nutcracker Man” in Olduvai Gorge, Tanzania; stone tools, pushes back age
of humans
(1974) “Laetoli Hominid 4”, Laetoli footprints in volcanic ash in Tanzania
(1978) “Lucy” in Hadar, Ethiopia
(1995) A. anamensis in Lake Turkana and Ethiopia
(1999) A. garhi in Bouri, Ethiopia
(2000) K. platyops “Man from Kenya with flat face”
ROBUST v. GRACILE
Robust – big faces and big teeth; debate over whether australopithecine or paranthropus
Australopithecus Australopithecus A. robustus
Kenyanthropus
Name
aethiopicus
boisei
platyops
“Black skull”
“Nutcracker”
1968
1959
1938
2000
Year found
Place found
Omo, Ethiopia
E. African Rift
Valley
South Africa
Lake Turkana,
Kenya
Age
2.6mya
0.9-2mya
3.5mya
Characteristics
-crests
-huge chewing
muscles
-huge teeth
-prognathic
-tiny brain
2.6mya –
1.5mya
-open habitats
-big teeth (2-3
times bigger
than chimps)
- crests; tall wide
face
- huge, deep
mandibular
corpus
- huge cheek
teeth
-small brain
-large, wide, flat
face
-big cheek teeth
-small earhole
-clay expansion?
*doesn’t fit*
Gracile:
Name
A. anamensis
A. afarensis
A. bahrelghazali
Year found
1995
1978
1993
A. africanus
A. garhi
1999
Place found
L. Turkana
and Ethiopia
Age
3.9-4.2 mya
Characteristics
Dentition:
-like chimp but
bigger teeth &
mandible, smaller
canines
Tibia:
-Built up bone on
medial side;
indicates
bipedalism
-notch in distal
elbow
(chimplike)
Tanzania,
Chad,
Ethiopia,
possibly South
Africa
3.5-3.6mya
Chad
South Africa
(Taung,
Sterkfontein,
Gladysvale)
Bouri, Ethiopia
3.5mya
2.9-1.6mya
2.5mya
Dentition:
-bigger cheek
teeth
-incisiform
canines
-smaller
incisors and
canines
Mandibular
fragment shows
thick enameled
premolars and
vertical
symphosis
-Like afarensis
but megadontal
-projecting
canines
-bigger, flatter
molars
-strongly
bicuspid (like
homo)
-slightly larger
brain than
afarensis
-deep
mandibular
fossa
-post crania
like A.
afarensis
“Little Foot”
-large postcanines
-small brain
-prognathic face
-large
browridge
-modern
postcranial
proportions
-bone smashing
indicates stone
tool usage
Different from
afarensis?
Crania:
-sexual
dimorphism
-chimplike
body size
-prognathic
-more
primitive than
Sahel.
Foramen
magnum
location and
zyg. arches
Lucy – longer
arms than legs;
bipedal
Dikika – 3yrs
old (3.3mya)
Lecture: March 1, 2007
Australopithecine Diets
How do we eat?
1) Ingestion – food in front of mouth (often incision)
2) Stage I transport – food goes to post-canine region
Oral transport – tongue shuttling food
3) Mastication – breakdown of food by (pre)molars (“chewing”)
Cheek teeth as pestles; move up and inward
Cusps = pestle; valleys = mortar
Unilateral mastication – chew on one side at a time (balancing side – side
you are not chewing on and working side – side on which you are
chewing)
Temporo-Mandibular Joint (TMJ) has 2 degrees of freedom:
1) Abduction (opening), Adduction (closing)  vertical motion
jaw closing muscles: temporalis (side of temporal lobe)
masseter (along cheekbone)
medial pterygoid (jaw joint to nose)
lateral pterygoid (jaw to ear)
jaw opening muscles: most important = diagastric
2) Translation (protrusion and retrusion)  horizontal motion
4) Stage II transport – formation of bolus, then to back of oral cavity
5) Swallowing
Deglutition (swallowing)
Humans: epiglottis and soft-palate are not in contact; shared space
for food and air which means much more likely to choke (only mammal
for which this is true)
6) Digestion
Salivary glands (amylase enzyme breaks down starches)
Stomach churns food and excretes acids to break it down
Small intestine – enzymatic breakdown
Liver secretes enzyme to remove waste and filter food
Pacreas
Long intestine – fermentation (microbes); primary water absorption
Humans: short long intestine and long short intestine (hi calorie, lo fiber diet)
Apes: opposite
Evidence for Australopithecine diet:
Tooth size, shape
Tooth microwear
Archaeology
Force generation
Isotopes
Force resistance
1) Tooth size:
A. Boisei – teeth 3x larger than humans
Megadontia quotient (tooth size per body mass)
A. Boisei < A. Africanus < A. Afarensis
Why have big teeth? – bite-force equivalent (bite force/surface area)
Very low bite force for humans (7.9) v. male chimp (13.1)
v. A. Bosei (22.1)
Stresses, however, are about the same (Boisei spreads stress over large
surface area)
2) Tooth shape:
- Spatulate incisors
- Incisiform canines
- Big front teeth – stripping pith (major fallback food)
- Molarized premolars; more “square shaped”, bigger; cusps
- Enamel thickness
Humans have slightly larger enamel compared to other A.
Prevents your teeth form wearing down; grinding
More cycles, harder food
3) Force generation and force resistance:
-- adaptations for chewing so much (spend most of their day eating) –
Force generation:
- cross-sectional area of muscle tells you how many muscle fibers you
have, the more the thicker
cross sectional area of temporalis (in the skull) shows you how
thick the chewing muscles are
orientation of temporalis (posterior v anterior)
force on front of teeth – posterior orientation
force on molars – anterior orientation (hominids)
-Mechanical advantage
(3rd class lever system)
condyle higher increases force
pull zygomatic forward, moves masseter forward,
increasing length of in-lever and creates more force
facial retraction and rotation
pull teeth inward to create shorter in-lever
-Wide zygomatic arches
sideways movement of jaw
tougher food generates horizontal motion
Force resistance:
resist generated force in order to not create microcracks
Mandibular strains (wishboning, twisting, bending)
Resist strain by putting mass in the plane of the strain
Facial twisting and bending
Make it more flatter, wider, and taller to resist force
Anterior nasal pillars
Putting it all together:
Chewing with high forces, but similar occlusal stresses
Big, thick teeth
High buttressed faces, mandibles
--- BECAUSE eating tough and hard foods (USOs and seeds)
Gracile (fruit/pith/USOs) v. Robust – tough diets, huge muscles etc. (fiber/tubers/seeds)
4) Tooth microwear:
Pits: harder, more brittle foods (seeds, nuts, bone)
Scratches: shearing tough food items (leaves or meat)
Both: intermediate foods (fruit) or mixed diets
--Strippers (Africanus) have more scratches than biters.-Molars: more scratches (gracile)
more piths
(robust)
Incisors: more wear (gracile)
Less wear (robust)
5) Isotopes:
**CARBON**
Carbon12 = stable, C13 also stable and C14 is radioactive
C3 plants – leaves, fruits, corn (browse)
C4 plants – grasses (graze)
Differences btwn C3 and C4: C4 plants have more C13
Sterkfontein: baboon and cerc. are closer to browsers and A. africanus are more in the
middle – ate a wide range of foods, but not sure which
Swartkrans: same picture with robust australopithecines (Homo A. robustus)
Final thoughts:
dietary shitft – less frugivory? More tough plants?
Shift between graciles and orbusts (more tough) - meat
Readings: B&S, Chapter 7
Chapter 7: Primate mating systems
 Primate females always provide extensive care for young; males occasionally
(mostly in monogamous bonds)
 Males do not care for offspring when can be using resource to acquire additional
mates or when extra care would not necessarily increase offspring fitness
 Females invest heavily in ea. offspring; reproductive success depends on ability to
obtain enough resources to provide for herself and offspring
 High-ranking females reproduce more successfully than low-ranking femalesfight to gain access to food and other resources
 Tradeoff between number of offspring and quality of care provided
 Shift in nature of care/attention; less as offspring grow
 Male reproductive habits dependent on distribution of females
 Sexual selection leans to adaptations that allow males to compete more effectively
for access to females; often stronger than natural selection
o Intrasexual selection (competition among males)
 Favors large body size, canines and weaponry
 In multi-male, multi-female groups where females mate with many
males, sexual selection favors higher sperm count **hence
Lieberman’s references to the benefits of larger testicle size**
o Intersexual selection (female choice)
 Favors: 1) increased male fitness, 2) good genes providing
increased offspring fitness, 3) traits making males more
conspicuous to females
 Only a few morphological traits developed to attract females
 Substantial variation in reproductive success of males over the course of their
lifetimes
 Infanticide as sexually selected male reproductive strategy; linked to changes in
male membership and status, shortens IBI, don’t kill own offspring
o Substantial reproductive benefits
o Female response: enlist aid of other males for protection or attempt to
confuse males about paternity
Reading: B&S, Chapter 11
Chapter 11: From Hominoid to Hominid
 Spread of woodland and savanna led to evolution of first hominids 6mya
 Differences between humans form other hominids: bipedalism, larger brains,
slower development, dental morphology, cultural adaptation (Ie. Language)
 A. ramidus similar to humans and chimps (foramen, locomotion, sm. Canines)
 Orrorin Tugamensis similarity to females
 Australopithecus, Paranthropus and Kenyanthropus lived in Africa between 24mya
 A. anamensis – bipedal but more apelike skull
 A. afarensis – E. Africa 3-4mya and is best known of the australopithecines
o Derived features shared with humans but ancestral traits include brain size
similar to apes
o Bipedal but not necessarily same efficiency of stride
o Laetoli footprints indicate another bipedal species in E. Africa at same
time as A. afarensis
o A lot of time in trees
o Sexually dimorphic in size
 A.africanus found in South Africa 3-2.2 mya
o Matured rapidly like chimps
 A. garhi around 2.5mya in E. Africa
 A. habilis/ rudolfensis
o Larger brain and more humanlike teeth ** probably not on test**
o Assigned to australopithecines because not as similar to homo
 Paranthropus aethiopicus = hominid with teeth and skull specialized for heavy
chewing
 Paranthropus robustus = more recent species found in S. Africa, very robust
 Kenyanthropus platyops = E. Africa between 3.5mya and 3.2mya
 Reasons for bipedalism:
o Efficient form of ground locomotion
o Erect posture allows hominids to keep cool
o Leaves hands free
o Harvesting of fruit from small trees
 Increased seasonality in rainfall favors a greater dependence on foods available
during dry season; corns, tubers, and meet
 Chimps as effective hunters but rarely scavenge
 Early hominids using tools like chimps did
 Chimps share food but very rarely except for mothers and offspring sharing
 Early hominids lived in multi-male, multi-female groups with little male
investment in offspring
WEEK 5
Lecture: March 6, 2007
Australopithecine Locomotion
Last common ancestor, something between chimps and humans, around 6 to 8 million
years ago
Chimp-like early hominids – like chimps, with bigger, thicker cheek teeth, might be
bipeds
Gracile and robust Australopithecines
How do we stand and locomote bipedally?
How does one shift from quadrupedialism to bipedalism? (What are adaptations for
bipedalism?)
What was early hominid bipedalism like? (and how would we figure it out?)
When and how did bipedalism evolve?
Why did it evolve?
Problem – what’s the relationship between form and function (of the bones we find)?
Form affects function is by performance – i.e. if I make my legs longer, I can walk more
effectively and use less energy  affected by natural selection and sometimes by habitual
activity (i.e. running not making your legs longer, but thicker, yet still more efficient)
typical quadrupeds: run and walk on their toes, fore/hind limbs are about the same length,
short digits, narrow chests, immobile shoulders, small tails
Arboreal quadrupeds (monkeys) have special adaptations – tend to run on feet rather than
just toes, very long olecranon process, scapulas are more on the side (shoulders more
mobile)
We evolved from arboreal, suspensory quadrupeds (apes) – very mobile shoulder and hip
joints, usually no tails, much shorter olecranon process, very long arms and fingers,
mobile wrists, and stabilized trunks due to shorter lumbar regions
Knuckle-walkers – still have dorsally placed scapula, kept long fingers which would
make it hard to walk on them, so used knuckles
Last common ancestor looked very much like knuckle walker
“Compromised adaptation” – long fingers so they’re able to grab branches, but can then
use knuckles to walk quadrupedally
Cost of locomotion – a human should cost 2 meters of oxygen per meters per gram of
body weight, etc.
When you put a chimp on a treadmill, it cost 150% more than in should have for a
mammal of its body mass, because of the knucklewalking
Chimps, knucklewalking has a locomotive energetic cost even though it’s useful
Now, bipedalism:
How much like us were the earliest bipeds?
Were they compromised or committed bipeds?
How much phylogenetic lag (how many features still remained in the body that were
useful for arboreality and quadrupedalism remained anyway because they weren’t
selected against?)
Posture
Bipedal posture – center of gravity is about behind one’s belt buckle
Quadrupeds – when it’s moving, it’s behind it’s shoulder; when they stand up, it’s way in
front of the hip joint; it’s over a nice rectangle of support, makes it hard to fall over
Bipeds have a smaller support area, which is why we fall over more easily
Postural adaptations for bipedalism – ability to stand up w/o a lot of energy, and to not
fall over
Standing up vs. lying down as a biped costs you about 7% more energy
Must get center of gravity right above hips to make standing more energetically efficient
Achieved this with our vertebral column, achieved by the curvature (lordosis) – the curve
centers the center of gravity above the hips (also causes lower back pain)
Postural adaptations for bipedalism in the skull – need to be able to orient your head so
it’s pointing forward; humans are able to look forward
For a chimp to stand upright, it would have to bend its knees the whole time
Close-packed hip and knee; can lock the hip in place, also the leg and hip
Bottom line – chimps don’t stand very well
Locomotion: gait (way in which you move your legs)
Two gaits; walking and running
Stride cycle = full cycle from heel strike to heel strike
1. Heel strike
2. Flat foot
3. Heel off
4. Toe off
5. Swing phase
6. Heel strike
Bold = “Stance phase”
When you walk, you always have one foot on the ground for about 60% of the stride
cycle
Body acts as an inverted pendulum – center of gravity rises and falls as you move
Human gait is so effective because, you store up potential energy in first half of stance,
then use it in the 2nd half – walking is basically a series of inverted pendular motions,
going up and down, and the potential energy of going up is used going down
While walking, several anatomical features minimize movement of center of gravity;
only moves around within a 5cm cube (flexed knee and hip, feet/knees lateral to
COG/pelvic tilt/thorax rotates with pelvis)
These features are visible in fossil record, which can help evaluate the way
australopithecines walked
Hip adaptations for bipedal locomotion
Humans have bowl-shaped pelvis
Australopiths have a tall pelvis
Small gluteal muscles – they’re abductors; while you’re walking, they keep your body
from falling over to the side; muscles originate on the hip, and articulate on the greater
trochantor
Bipeds need larger femoral heads because all of our body weight goes on them, unlike
quadrupeds, and we need a long femoral neck
Femoral head size can be indicative of body weight
Pelvis
When a chimp goes through the birth canal, it doesn’t have to twist
In a human, the baby starts in the birth canal with the nose sideways, then rotates
Lumbar column – human lumbar vertebrae are wedged (top and bottom of the vertebrae
are not parallel)
In chimps, the width remains constant as you go down
In humans, the fifth lumbar vertebra is wider than the first
The knee – the femur is oriented inward toward the knee (bicondylar [carrying] angle];
angle is steeper in australopithecines than humans because their legs are shorter, and to
get their knee under the center of gravity, angle must go inward quicker
Ankle and foot – arch in foot, which allows humans to stiffen the foot and use the toes to
push off the ground; chimps have no arch in their feet
Human feet – weight transfer from lateral to medial side; short, straight toes, big
adducted big toe (hallux)
Chimp feet – no weight transfer (mostly lateral), longer curved toes, smaller abducted big
toe (useful for climbing trees)
Foot arch acts as an arch when humans run
Heel bone – because of the heel strike component of walking, all your body weight goes
through this bones; generally there’s a linear relationship between size of heel bone
(calcaneus) and body mass in mammals
Most incontrovertible evidence that australopithecines were bipeds is the Laetoli
footprints (in Tanzania), about 3.6 million years old; consists of 3 individuals, 2 of whom
walked in the footprints of the larger individuals
Footprints show that they were well-adapted for terrestrial, bipedal locomotion
Arboreal adaptations
Little foot – didn’t have a full arch like humans
Limb length – in apes, very long arms relative to legs; humans have short arms relative to
legs; Lucy is right in the middle
Longer legs make locomotion more efficient; short legs are more efficient for climbing
because they direct the center of gravity toward/into the tree
Limb mass – in a chimp, about 16% of mass is in arm, 24% in leg; in humans, 8% in
arms, 30% in legs; australopithecines. 12% in arms, 28% in legs (closer to the chimp)
Shape of thorax – humans have relatively wide upper thorax, shoulders towards the back;
apes and australopithecines have narrow upper thoraxes and permanently shrugged
shoulders – more efficient for climbing; rotation of scapula isn’t needed with this design
if you want to get your arms above your head
How did australopithecines walk?
Bipedal adaptations:
1) Hip abductor
2) Bicondylar angle
3) Long femoral neck* - more efficient than humans
4) Reinforced knee
5) Lumbar curve
6) Plantar arch
7) Abducted hallux
8) Wide sacrum
Arboreal adaptations
1) Long curved toes
2) More flexible ankle
3) More flexible big toe
4) Superiorly oriented shoulders
5) Short legs
6) Funnel shaped thorax
Australopithecine gait – would it be upright, or with a flexed knee and hip (similar to a
chimp)?
Much of this debate cannot be answered by the data we have
It’s been assumed that having a flexed hip and knee is bad, but most animals have that
There are costs and benefits to both sides –tradeoff between efficiency/mechanical
advantage and speed; flexed hip/knee gives more speed (that’s why the natural position
when you’re scared is to crouch; lowers your center of gravity, gives you more stability,
prepares you to accelerate better should you need to run)
The force that muscles are able to produce do not scale with body size, so bigger animals
tend to have more extended postures – otherwise, it would cost incredible amounts of
energy to move
Humans weigh more than australopithecines, therefore we should have more extended
limbs
Laetoli footprints – in the typical human, you go from the lateral size of your foot to the
medial side, so the footprint is deeper in some areas; in the footprint, the deepest portions
are roughly down the middle, hints at differences in force distribution of the foot
Australopithecines were probably compromised bipeds
When and why did bipedalism evolve?
Evidence suggests it was in sahelanthropus about 6 or 7 million years ago
Earliest hominids appear to be upright bipeds
Why did it evolve? Some hypotheses:
1) Locomotor efficiency
2) Postural hypothesis (not likely)
Browsing in trees to pick berries
Seeing over tall grasses
3) Carrying (food, tools/weapons, infants)
4) Thermoregulation – standing upright reduces the amount of radiation your
body gets
5) Fast feeding on grass/seeds
6) Provisioning mates
7) Threat displays (throwing stuff at people)
8) Swimming (aquatic apes hypothesis … ignore this, it’s stupid)
Consequences of bipedalism
Adaptations – feature favored by natural selection for its present function
Exaptation – things that the feature later allowed for, but wasn’t selected for (i.e. we can
type, but we didn’t become bipeds so we could type)
Running – early australopithecines were probably not good at running; they might’ve
been good sprinters like chimps, but not good at distance running (as humans are)
Lecture: March 8, 2007
Australopithecine Phylogeny and Life History
Systematics – the species that we have and their evolutionary relationships
Early hominids, then 2 groups of australopithecines: gracile and robust; we don’t know if
they’re really that different
Orrorin may not even be a hominid
What are the taxonomic units? (species)
Determine their evolutionary relationships
Cladogram (how closely things are related
Phylogeny (ancestor/descendant relationships)
Test hypotheses of causation (scenario of what might’ve been the selective forces that led
to certain species, etc.)
Bones are influences by a combination of combination of genetic and non-genetic
stimuli, so we can’t just look at DNA (there isn’t any left anyway); non-genetic stimuli
doesn’t tell you anything about selection
Must not assume that the shapes of bones always show genetic information
Definition of species – no agreed upon definition
Biological Species Concept (BSC) – a set of actually or potentially interbreeding
organisms
Phylogenetic species concept (PSC) – group of organism who share single
common ancestor,
distinguished by a unique combination of features (apomorphies –
unique, derived features)
BSC – you can’t test it with fossil record
Doesn’t account for change over time
Phenotypic variation often a poor guide to reproductive isolation
PSC – convergence happens (similarities that evolve independently)
Doesn’t account for variation
Variation: We can measure variations in populations – sources of variations: sexual
dimorphism, age, population, time, other; biggest source is sex. One standard deviation
in an equally distributed group will give you 68% of the variation around the mean. So,
if a feature falls outside the standard deviation of a species, it’s most likely from another
*But, the problem is that different features will give different answers
Why?
May not be a different species
Effects of non-genetic variation (plasticity that causes “noise”)
Not all features change between species (e.g. having 2 eyes)
Typical heritability of most skeletal features is around 30%, which means there are lots of
factors influencing the fossil record
Derived characters
Only things that have changed and exhibit modification provide information about
evolutionary events
If you don’t have any genetic data, how do you know you’re right?
One issue is the number of species you’re willing to accept into your analysis – do you
err on the side of too many (splitter) or too few (lumper)?
Logically, you’re better off erring on the side of too many, you’re better off being a
splitter than a lumper
A lot of these species ideas are based on one sample  that’s a problem
Evolutionary relationships
Cladogram is a tree that simple tells you the evolutionary relationships between species,
doesn’t tell you who is descended from whom (no time in a cladogram)
Phylogeny adds time to a cladogram, shows what is descended from what
How to make a cladogram
1) Choose/define taxa (Operational taxonomic unit – what we think is a species,
but not sure)
2) Choose/define characters (aspects of organisms that we can compare)
What makes a good character?
Criteria:
Biological (i.e., the day of the week that you found the fossil
doesn’t count)
Objective/quantifiable
Very more between than within taxa
Independent
Result from heritable processes
Homologous = similar because of common ancestry, not because
of independent evolution  circular logic
Best character – DNA
Skeletal data as characters – complex, integrated, subject to nongenetic causes of variation
Vault thickness – not a good character
3) Determine polarity (ancestral/primitive vs. derived) – 5 toes is ancestral,
having hair is derived – how to figure this out? The outgroup method: imagine
you have a group of creatures
Character conflict – when different characters give you different trees
Scientists use Occam’s razor – idea that the simplest solution is the most
likely, so they
select the most parsimonious tree (one that requires the
fewest splits); if any trees are equally parsimonious, add another character
Problems with parsimony
a) Function of # and type of characters used
b) Non-independence
c) Is evolution really parsimonious? No.
Overview of how to make a cladogram
1) Choose/define taxa (OTUs)
2) Choose/define characters
3) Determine polarity
4) Identify synapomorphies (shared derived features) – problem, character conflict
5) Pick the best tree (using parsimony/homology)
But there are still problems – why?
Example, with human/chimp/gorilla tree, we got it wrong because we got
primitive vs. derived wrong – never would’ve figured that out without the genetic data
Strait and Grine (2004)
1) Taxa included, chose their specimens
2) Defined the characters to be used
3) Used outgroups to figure out the character states (polarity)
4) Most parsimonious cladogram – results in all robust australopithecines came
together, most of the others got separated out
There’s no guarantee of getting the right answer
You can step back in the taxonomic hierarchy and look at genus
Ontogeny (Life History)
Teeth have a clock-like schedule of eruption that’s related to different phases of ontogeny
Humans first molar erupts around 6 years old, chimps and monkeys erupt closer to 1 year
old
If you graph brain mass with the age at which your first molar erupts, you get a pretty
good line, also, if you know when the first molar erupts, you can find when your brain
stopped growing
Tong baby – first molar is just erupting; how old was he?
Teeth have striae of retzius (much like tree rings) – every 7 days, the emiloblast takes a
break from squirting out enamel and leaves a line of hyper-mineralized enamel; lets you
find out how long it took the tooth to erupt
Australopithecines have thicker enamel and larger teeth because they extruded enamel
faster and grew their teeth faster than an African ape
Tong baby erupted its first molar around 3 years old
Macaques grow really quickly
Australopithecines are almost identical to chimps in their growth process
Reading: B&S, Chapter 9
Primate Life Histories and the Evolution of Intelligence
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Primates have both big brains and long lives – the two features are correlated
Life history theory: focused on the evolutionary forces that shape trade-offs
between the quantity and quality of offspring and between current and future
reproduction
Aging and death result from trade-offs between reproduction at different ages and
survivorship
The tradeoff between survival and reproduction is greatly biases against
characteristics that prolong life at the expense of early survival or reproduction
The tradeoff between current and future reproduction and between quantity and
quality of offspring generates constellations of interrelated traits
The benefits derived from current and future reproduction depend on a variety of
ecological factors that influence prospects for survival
Natural selection not only shapes the relationship between life history traits, but it
can also shift the values of these traits in response to changes in environmental
conditions
Primates fall somewhere along the slow/long end of the life history continuum
The first adaptive change in the package of life history traits within the primate
order involved the origins of the prosimians and their shift to an arboreal niche –
60 mya
The second major adaptive shift is associated with the appearance of anthropoid
primates – monkeys and apes – 35 mya
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The third adaptive shift is associated with the great apes who appeared during the
Miocene epoch, about 20 mya
Great apes rely on complex extractive foraging techniques, sometimes using tools,
to a greater extent than most other primates
Ecological hypotheses for the evolution of intelligence predict that specific
characteristics of the diet or the environment of particular primate species will be
correlated with their cognitive abilities
The social intelligence hypothesis predicts that there will be a positive correlation
between the complexity of social life and the neocortex ratio
Comparitive analyses provide support for both the ecological hypotheses and the
social intelligence model
Monkeys and apes construct mental maps of their home ranges, allowing them to
move efficiently from one food source to another
There is evidence that monkeys and apes know something about the nature of
kinship relationships among other members of their groups, and some evidence
suggests they may understand the nature of rank relationships among individuals
Understanding of third-party relationships may be particularly useful in managing
coalitions
Primates may understand more about the behavior of other animals than about
their feelings, thoughts, intentions
The ability to predict what others will do might be based on a sophisticated ability
to track contingencies between one event and another or on knowledge of other
animals’ mental states
Great apes may have more knowledge of the minds of others than monkeys
Key terms
Neocortex – part of the cerebral cortex, generally though to be most closely
associated with problem solving and behavior flexibility; in mammals, it covers
the entire surface of the forebrain
Extracted foods – foods that are embedded in a matrix, encased in a hard shell,
etc.
Social intelligence hypothesis (see above)
Neocortex ratio – the size of the neocortex in relation to the rest of the brain
Executive brain – composed of the neocortex and the striatum (see below), a
structure in the basal ganglia that is functionally linked to the neocortex
Brainstem – the portion of the brain that lies between the cerebrum and the spinal
cord, and provides the major route for communication between the forebrain, the
spinal cord, and the peripheral nerves
Striatum –a structure composed of two of the basal ganglia of the forebrain: the
caudate nucleus and the putamen
Tactical deception – the use of normal parts of an animal’s behavioral repertoire
in an unusual context to achieve specific objectives that are beneficial to the actor
Cognitive map – a mental representation of the location of objects in space and
time that allows for efficient navigation
Third-party relationships – relationships among other individuals
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Redirected aggression – a behavior in which the recipient of aggression threatens
or attacks a previously uninvolved party
Theory of mind – the capacity to be aware of the thoughts, knowledge, or
perceptions of other individuals
Reading: Lovejoy 1988
This article discusses Lucy, the australopithecine fossil. It’s focused mainly on
examination of the pelvis, and the features of the pelvic area that indicate that Lucy was
adapted for bipedalism. It goes into a lot of detail about muscle motion, etc. that
hopefully we won’t need to know, because there was a lot of it. Most of the article just
reiterates the things we learned in lab 4, so see those handouts if you really want all the
anatomical detail. The takeaway point, I’d say, is that Lovejoy is under the impression
the Lucy was a dedicated biped, because he believes that without the species habitually
walking upright, it never could have developed the adaptations that consistently made
them better at it. Also, he feels that examination of her other features (upper body, knees,
etc.) show that she was ill-suited for climbing – for example, the arms and fingers are
shorter, which is bad for climbing. Because he thinks Lucy was a dedicated biped, he
believes that bipedalism must have predated her by quite a lot, and that her ancestors
must have left the trees and started walking around long before Lucy, which would
explain why she’s such an awesome biped.
WEEK 6
Lecture: March 13, 2007
My Life as an Australopithecine
Vital Statistics
 Why are we so interested in size and dimorphism?
o Tells us a lot about locomotion, diet and reproduction, competition, etc.
 The Index of Dimorphism (ID) = (size of male)/(size of female)
 CV = Coefficient of Variation, a standardized method of variation
o CV = (standard deviation)/(mean*100)
o One standardized deviation, standardized by the mean
 The more dimorphism, the higher the CV
 Regression equations: how we estimate body size and dimorphism form
skeletons
o In order to do this, we needs lots of bones of australopithecines, and we
haven’t had as many complete skeletons as we would like (i.e. male
counterparts to Lucy)
 A lot found in Ethiopia, Hadar- helped with figures
o So, how do we estimate the ID?
 Estimate the ID from the CV
 Estimate the ID from likely males and females
 Both methods give similar results for A. afarensis
 Australopithecines were similar in body mass to chimps, but more sexually
dimorphic because of male (not female) body size.
o But how did we infer this? Induction v. Deduction
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Deduction: argument deduction valid if the conclusion makes no
factual claim not (at least implicitly) made by the premise
 Most scientists comfortable with this type of argument
 Induction: argument induction strong if factual claims go beyond
factual information in premises
 What most evolutionary biologists have to do
o Regression based arguments are inductive
 How do we evaluate the strength of an inductive inference?
o Power of Prediction (how generalizable)
o Mechanistic basis behind assumption
 What other inferences can we make?
o Brain size (encephalizaiton quotient) can show us brain size v. body size,
but we need the estimated body mass. Then we can see how much larger
its brain is in relation to its body.
 Based on knowing if we have the right brain and body size
estimates
o Tooth dimorphism- looking at cheek and canine sizes, more dimorphic in
molar size but less dimorphic in canine size
o Face dimorphism- pretty dimorphic face-wise, males had bigger faces than
females. Dimorphism greater than chimps and closer to gorillas.
o Height from regression, legs shorter/arms longer than humans, apelike
(stout) torsos
Habitat
 Know these 4 eras:
o Holocene
o Pleistocene
o Pliocene
o Miocene
 Global shift from more forests to less forests in the last few million years
o In Africa the great rift valley systems also developed during this period
 No apes/chimps live in areas with more than 4 months dry season, but hominid
fossils found mostly in places with dry seasons longer than 5 months; no fossil
apes found in these habitats
o Clear ecological separation
 Global climates fluctuate continually from warmer to cooler mainly b/c of regular
changes in the earth’s orbit and axis tilt
o Other factors also implicated (rifting, continental drift)
 What happens when habitats become less forested and more open?
o Resources (food and safety) become dispersed but are sometimes clumped
in large patches, distribution of food, safe sleeping spaces and predator
changes
o Fruits more seasonal and well-protected, plants store more energy
underground
 Hypothesis: Hominids would be only one of many types of species that change
over this period.
Reading: B&S, Chapter 7
Chapter 7: Primate Mating Systems
 Mating systems- the way animals find mates and care for offspring, plays a crucial
role in understanding primate societies
o “Understanding the diverse reproductive strategies of nonhuman primates
illuminates human evolution because we share many elements of our
reproductive physiology with other species of primates.”
The Language of Adaptive Explanations
 Strategy refers to behavioral mechanisms that lead to particular courses of
behavior in particular functional contexts, such as foraging or reproduction
 The terms cost and benefit refer to the effect of particular behavioral strategies on
reproductive success
o Beneficial: increase genetic fitness of individuals
o Costly: Reduce genetic fitness of individuals
The Evolution of Reproductive Strategies
 Primate females always provide extensive care for their young, but males do so
only in a few species.
o Males do not care for their offspring when:
 They can easily use their resources to acquire many additional
matings
 Caring for their offspring would not appreciably increase the
offsprings fitness
 Ideas of investing and non-investing male parents deal with the idea that caring
for offspring takes time and effort away from competing for access to females,
getting food, etc.
 Unequal parent investment (one cares for offspring more htan other) favored
whne one or both of these is true:
o Acquiring additional mates is relatively easy, so considerable gains are
achieved by allocating additional effort to attracting mates
o The fitness of offspring raised by only one parent is high, so the payoff for
additional parental investment is relatively low.
 The mammalian reproductive system commits primate females to investing in
their offspring; females lactate and males do not
Reproductive Strategies of Females
 Female primates invest heavily in each of their offspring because:
o Pregnancy and lactation are time-consuming; pregnancy takes so long b/c
brain tissue development a slow process
o It takes so much time and energy, so females can only have a few
offspring in their lifetimes
 A female’s reproductive success depends largely on her ability to obtain enough
resources to support herself and her offspring
 Changes in resources can affect females’ ability to reproduce or support their
offspring
 Sources of variation in female reproductive performance: high-ranking females
tend to reproduce more successfully than low-ranking females (have high priority
access to valued foods)
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Reproductive trade-offs: females must make a trade-off between the number of
offspring they produce and the quality of care that they provide
o There is sometimes conflict between mothers and infants over the amount
and extent of maternal investment.
 Parent-offspring conflict: a fundamental asymmetry in the genetic
interests of mothers and their offspring
Sexual Selection and Male Mating Strategies
 Sexual selection leads to adaptations that allow males to compete more effectively
with other males for access to females
 Sexual selection often much stronger than ordinary natural selection
 Two types of sexual selection:
o Intrasexual selection resulting from competition among males; in species
in which females cannot choose their mates, access to females will be
determined by competition among males
o Intersexual selection resulting from female choice; selection will favor
traits that make males more attractive to females.
 Intrasexual Selection
o Competition among males for access to females favors large body size,
large canine teeth and other weapons that enhance male competitive
ability.
o The fact that sexual dimorphism is greater in primate species forming onemale, multimale groups than in monogamous species indicates that
intrasexual selection is likely the cause of sexual dimorphism in primates
o In muiltimale, multifemales groups, where females mate with several
males during a given estrous period, sexual selection favors increased
sperm production.
 Intersexual Selection
o Favors 3 kinds of traits in males:
 Traits that increase the fitness of their mates
 Traits that indicate good genes and thus increase offspring fitness
 Nonadaptive traits that make males more conspicuous to females
Male Reproductive Tactics
 Investing males
o Monogamous pair-bonding is generally associated with high elvels of
paternal investment. In species with this, males do not compete directly
over access to females.
o In cooperatively breeding species, males invest heavily in offspring, but
the reproductive benefits to males are not clear.
 Male-male competition in non-monogamous groups
o In non-monogamous groups, the reproductive success of males depends on
their ability to gain access to groups of unrelated females and to obtain
matings with receptive females.
o In species that normally form one-male groups, males compete actively to
establish residence in groups of females
o Residence in one-male groups does not always ensure exclusive access to
females
o For males in multimale groups, conflict arises over group membership and
access to receptive females
o There is growing evidence of substantial variation in the reproductive
success of males over the course of their lifetimes.
Infanticide
 Sexually selected male reproductive strategy
o Associated with changes in male residence or status
o Males kill infants whose deaths hasten their mother’s resumption of
cycling
o Males kill other males infants and not their own
o Infanticidal males achieve reproductive benefits
 Can be a substantial source of mortality
 Females have evolved some responses (support of other males, confusing males
about paternity of infants)
 Still a controversial idea
Reading: B&S, Chapter 8
Chapter 8: The Evolution of Social Behavior
Kinds of Social Interactions
 Social interactions are behaviors that affect the fitness of more than one individual
o Dyadic/pairwise interactions: interactions that involve two individuals
 Actor: individual performing behavior
 Recipient: individual affected by behavior
o An act is beneficial if it increases fitness, it is costly/detrimental when it
reduces fitness
 Different kinds of interactions:
o Selfish: beneficial to actor, costly to recipient
o Altruistic: costly for actor, beneficial to recipient
o Mutualistic: beneficial to all
o Spiteful: costly for all
Altruism: A Conundrum
 Altruistic behavior cannot evolve by ordinary natural selection because it
decreases the fitness of the individual performing the behavior.
 Primates perform altruistic behaviors in nature
 Altruistic behaviors cannot be favored by selection just because they are
beneficial to the group as a whole
Kin Selection
 Natural selection can favor altruistic behavior if altruistic individuals are more
likely to interact with each other than chance alone would dictate
 When individuals interact selectively with relatives, altruistic acts are more likely
to benefit the genes of those for whom the act is costly
 Hamilton’s Rule: Hamilton’s theory of kin predicts that altruistic behaviors will
be favored by selection if the costs of performing the behavior are less than the
benefits discounted by the coefficient of relatedness between actor and recipient.
According to Hamilton’s rule, an act will be favored by selection if:
o rb > c
o
o
o
o

r = average coefficient of relatedness between actors and recipients
b = sum of fitness benefits to all individuals affected by behavior
c = fitness cost to the individual performing the behavior
Two insights from H’s rule: altruism is limited to kin; closer kinship
facilitates more costly altruistic actions
Evidence of kin selection in primates
o Primates may use contextual cues to recognize maternal relatives
(phenotype matching)
o Phenotype matching may play some role in paternal recognition
o Food sharing, grooming among kin