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93 Cards in this Set

  • Front
  • Back
• Relationship of humans to African and Asian apes
Darwin was correct that humans are more closely related to African apes (gorillas and chimps) than Asian apes (orangatangs and gibbons). Evolutionary systems put all apes on one branch and humans on another but those systems were wrong.
• Distinguishing features of primates:
binocular vision and prehensile hands with opposable thumbs
• Prosimii, Tarsiiformes and Anthropoidea
Three suborders of primates:
- Prosimii: lemurs, galagos and lorises (retain ancestral, elongated faces)
- Tarsiiformes: tarsiers (shortened snout and more forward-pointing eyes)
- Anthropoidea: monkeys, apes and humans (larger brains)
• Hominoidea (Apes): who are they and what are their shared, derived characters?
Better known as apes
• Includes gibbons, orangutan, gorillas and chimpanzees (closest relative to the humans)
• Shared, derived characters of the Hominoidea are:
- reduction (loss) of tail
- evolution of shoulder blades enabling swinging from branch to branch
• Primate genome sequencing: why is macaque genome important?
Humans and chimps share 98.7% genome although primitive versus derived genomes cannot be distinguihed. The Rhesus macaque was the most recent genome to be mapped in April of 2007.
• Chimpanzee versus Bonobo social systems
• Chimpanzee
- Male dominated and aggressive
- Females disperse but males remain in natal territories so males tend to be related
- Males conduct murderous raids on neighboring communities
• Bonobo
- Female dominated and conciliatory
- Sex is used as a greeting and as a means of
conflict resolution
- Sexual and social bonding in females
prevents male domination
- Individuals prefer sexual contact within
group over violent confrontations with outsiders
• Punctuated equilibrium: what is it, how can it be explained and its relevance to human evolution
Puncuated equilibirium is long periods of morphological stasis followed by rapid
bursts of evolutionary
change. Once an evolutionary
equilibrium is reached,
why should there be
evolutionary change?
• Often rapid
evolutionary change is
associated with major
geological events and
climatic changes. Punctuated
environmental changes due to geological events and climate
• Reorganization of the phenotype due to changes in timing and rate of developmental processes
(heterochrony). Major transitions in human evolution
associated with dramatic
changes in global climate
- evolution of bipedalism
6 to 7 mya
- split between Australopithecus and Homo 2.5 to 3 mya
• Heterochrony and differential growth rate in human evolution
- change in timing of
developmental events,
leading to alterations of
size and shape
- fetal head shapes in human
and chimp very similar
- changes in small number
of regulatory genes
affecting relative growth
rates can dramatically
affect adult phenotype
• Subfamily Hominini (lineage leading to modern humans after split from chimpanzee)
• Lineage leading to modern
humans is subfamily Hominini
• Molecular estimates indicate
human-chimp split at 6.5
million years ago
• Oldest fossil hominin is
Sahelanthropus tchadensis,
estimated to be 6 -7 million
years old
• Best known early hominin is
Australopithecus afarensis
• Last hominin to go extinct was Homo neanderthalensis,
28,000 years ago
• Sahelanthropus tchadensis: oldest hominin
Earliest known Hominini,
Sahelanthropus tchadensis
• Found in Chad (reported in
Nature, July 2002)
• Estimated to be 6–7 million
years old
• Fossil consists of cranium,
jaw fragment and several
• Mixture of chimp &
australopithecine features
• Orbital plane, foramen magnum evidence for bipedalism in Sahelanthropus tchadensis
Skull revelations
• Chimpanzee
- walks on all fours (knucklewalking
- quadrapedalism reflected in
anatomy of head
- acute angle (650) between
foramen magnum and orbital
• Human
- bipedal
- spinal cord enters brain on
nearly vertical line
- creates larger angle with
orbital plane (1030)
- indicates head held upright
• Sahelanthropus
– 950 angle suggests that species held
head upright and was bipedal
• Ardipithecus: where found and how old
Known primarily from dental
structures and fragmented
skeletal remains
• Ardipithecus kadabba
- Ethiopia
- 5.2 to 5.8 mya
- jawbone, teeth, arm
fragments, collarbone and toe
- form of toe bone suggests
upright posture
• Ardipithecus ramidus
- Ethiopia
- 4.4 to 4.5 mya
- jawbone, teeth and arm
Best known, early Hominini
• Australopithecus afarensis (Lucy and the Dikika baby)
Australopithecus afarensis
• Taken from sites in Ethiopia
(Hadar) dated at 2.9 to 3.5 mya
and 3.6 mya in Tanzania
• Best preserved specimen was
Lucy from Hadar
- skeleton 40% complete
• Site in Tanzania
- famous because skeletal remains
found in association with 3.6 myo
- proves A. afarensis was bipedal
• Mosaic evolution in Australopithecus afarensis
Mosaic evolution
• Morphologically intermediate between
human and ape
• Bipedalism clearly indicated by pelvic
• Small-brained (slightly larger than
• Intermediate dentition
– reduced canines
– shortened jaw
– herbivorous diet
• Hypotheses for bipedalism: which is best supported and most parsimonious?
Hypotheses for bipedalism
• Man the hunter
• Man the scavenger
• Woman the gatherer
• Man the provisioner

Most parsimonious explanation was that Bipedalism was fueled by fragmentation of the
• Differences between the genera Australopithecus + Paranthropus versus Homo: encephalization and dentition
Between 2 and 3 m.y.a., 4 to 5 species of hominins co occurred in Africa
• Small brains, large cheek teeth -- Genera Australopithecus and
• Large brained, small cheek teeth -- Genus Homo
Robust australopithecines
(also called Paranthropus)
• Adapted for feeding on
tough plant foods
– enormous cheek teeth
– robust jaws
– massive jaw muscles
anchored to bony crest at top of skull
– nicknamed “the nutcracker man”
• All extinct by 1 m.y.a.
• Homo habilis/rudolfensis
Homo habilis/rudolfensis
• First Homo species (2.4 - 1.6 mya)
• Transition from Australopithecus to Homo involved increased
encephalization and decreased dentition
• First big-brained hominin
- brain size of 750 cm3 (Gorilla 400 cm3;
Australopithecines 500 cm3; human 1350 cm3)
• Definitely used stone tools
- unclear whether australopithecines used tools
- oldest stone tools dated at 2.4 mya
• Strongly sexually-dimorphic
• Hominid and ape brain/body size allometry
• Comparisons of
brain sizes should
correct for
differences in
body size
• Genus Homo
– abrupt increase in
ratio of brain to
body size
• Homo ergaster/erectus
• Evolved in Africa 1.8 mya (H. ergaster)
• Populations spread to Middle
East, Asia and Europe
• Went extinct between 50,000
and 100,00 years ago
• First appearance outside Africa (H. erectus)
• First appearance of systematic hunting
• Well-defined home bases
• Advanced tools, e.g., axes
• Use of fire
• Brain size ranged between
850-1100 cm3

Turkana boy
• Discovered in 1984 at Lake
Turkana, northern Kenya
• Virtually complete specimen of
Homo erectus boy
• Well-dated deposits 1.6 mya
• Compared to modern humans
- thick cranial bone
- prominent brow ridges
- low, flat forehead
- thick femur
- heavy musculature
- thinner spinal cord
• Homo floresiensis
From Indonesian island of
• Fossils dated at 18,000
years old
• 1 to 1.5 m tall
• Bipedal
• Found with stone tools,
dwarf elephants and
Komodo dragons
• Mosaic of primitive and
derived traits
• Brain size and stature of
• Facial and dental morphology of Homo
• Origin of modern humans: Candelabra versus Multiregional versus Out-of-
Africa models
Candelabra model
• Proposed that three geographic
populations of H. erectus independently
evolved into H. sapiens
Multiregional Model
• Argues for a geographically widespread
transformation from Homo erectus to
modern Homo sapiens with some gene
flow between populations
Out of Africa = African Replacement =
Uniregional Model
• Argues for a geographically discrete
origin of H. sapiens in Africa followed
by migration and replacement of H.
erectus populations
• Mitochondrial Eve hypothesis
• Based on study of human mitochondrial DNA by Cann et al. (1987)
• Phylogenetic analysis indicated that base of tree consisted entirely of
mitochondrial haplotypes(genotypes) from Africa
• Proposed that all current human mitochondrial haplotypes could be traced
back to mitochondria of a single female in Africa 200,000 years ago -
Mitochondrial Eve hypothesis
Does not mean that only one female existed at that time - only that other mitochondrial
lineages have since gone extinct

Mitochondrial Eve hypothesis explained:
• Mitochondrial DNA study did not demonstrate existence of an Eve (a single female alive
200,000 years ago)
• Does indicate that most recent common ancestor (MRCA) of all humanity via
mitochondrial pathway existed in Africa 200,000 years ago
• Based on coalescent theory for mtDNA
- concept that all maternal lineages trace back to
single mother in ancestral population
- only females transmit mitochondria to offspring
- each generation, some women have no children and others have only sons
- working backwards towards common ancestor, this reduces number of women who have
contributed mitochondria to current population until only one remains
- consequently, all men and women carry mitochondria inherited from single woman
- nuclear genes from many contemporary women of Mitochondrial Eve are present in today's population, but mitochondrial DNA from them is not
Origin of Homo sapiens: mtDNA perspective
Limitations of Cann et al. (1987)
• Based on outdated method of
inferring mitochondrial DNA
sequence (restriction fragment length polymorphisms, or RFLPs)
• Did not use outgroup to root tree

More recently
• Ingman et al. (2000) repeated study using 53 complete sequences of
mitochondrial genome
• Chimpanzee used as outgroup
• Cann et al. (1987) were right!
• All men and women carry same
mtDNA derived from Mitochondrial Eve 171,500 years ago
• Over time, mtDNA has accumulated different mutations
• First three branches (L0, L1 and L2) contain only sub-Saharan sequences
• All women outside Africa descend from M or N, two daughter lineages of L2
• Y-chromosomal Adam perspective on human origins
• Only men have Y chromosome
which does not recombine with X
• Each generation, some men have no children and others only daughters
- sexual selection on males increases
variation between individuals in
number of offspring produced
- reduces coalescence time of Y chromosome compared to that of
• Working backwards towards
common ancestor, this reduces
number of males contributing Y
chromosomes to current population until only one remains
• Consequently, all men carry Y chromosome inherited from a
single individual, the Ychromosomal Adam
• Although all men carry Y chromosome from same ancestor, different mutations have gradually accumulated
• First two branches in Y-tree are sub-Saharan
• All male lineages outside sub-Saharan Africa carry derived M168 mutation
• Coalescent theory: all extant human Y chromosomes descended from single man, Y-chromosomal Adam, who lived in Africa 90,000 years ago
• Again, name incorrectly implies that Ychromosomal
Adam was only living
male of his time - he was not
- autosomal genes from many
contemporary men of Y-chromosomal Adam are present in today's population
- however, only Y-chromosomal Adam produced unbroken line of male descendants carrying his Y chromosome
• Newly discovered AMHS fossils from Ethiopia (160,000 years BP)
- oldest anatomically modern Homo
sapiens (AMHS) fossils recently
discovered in Ethiopia
- dated at 160,000 years ago
• Middle East
- next oldest AMHS
- Qafzeh site in Israel
- dated at 90,000 years ago
• Asia/Australia
- precise dates controversial
- 40,000 to 50,000 years ago
• Europe
- dominated by Neanderthals until 30,000
years ago
- AMHS do not appear in eastern Europe
until 40,000 years ago
- AMHS do not appear in western Europe
until 32,000 years ago
• Fossil evidence also supports Outof-
Africa hypothesis
• Consensus view of genetic and fossil evidence for Multiregional versus Out-of-
Africa models
Fossil evidence consistent with Out-of-Africa model
• Molecular evidence based on mitochondrial DNA, Y-chromosomal DNA and autosomal
DNA all support relatively recent origin of Homo sapiens in Africa
• Analyses of DNA sequences from MHC loci, mitochondria and Y-chromosomes all indicate
that genetic diversity is greatest in Africa
• Most probable scenario is that modern Homo sapiens are derived from geographically
discrete population that evolved in Africa 150,000 to 200,000 years ago
• Pattern of exodus of Homo sapiens from Africa: when and to where?
conditions, sea level
230 feet lower than
• Humans crossed Red
Sea, gradually
expanding along the
the coast in
• Arrived in Australia by
45,000 years ago
• This pattern of
migration explains
existence of darkskinned,
peoples in New
Guinea and Australia

Why exodus via the southern route?
• Migration into Europe not achieved until 35,000 to 40,000 years ago
• Neanderthal: historical duration, geographic distribution and molecular
evidence of relationship to Homo sapiens
• Dominant hominin fossil in
Europe and Middle East
between 300,000 and 30,000
years ago
• Coexisted w/ Homo sapiens
(Cro-Magnon man) in Europe
between 40,000 and 30,000
years ago
• Extinct by 28,000 years ago
• Stocky, barrel-chested and
very muscular
• Remains include many broken
and healed bones
• Evidence of cannibalism - cut
and burned bones at several

• In 1997, Krings et al.
succeeded in sequencing
360 bp of mitochondrial
DNA from the femur of
the Neanderthal type
• The average pair-wise
divergence between
human-Neanderthal is 27
substitutions compared to
an average of 8 differences
between geographic
populations of Homo
• Neanderthal genome sequencing project
The Neanderthal Genome Sequencing Project
• Neanderthal Genome Sequencing Project (NGSP) based on a new
sequencing technology developed by 454 Life Sciences
• Sequences genome in small fragments which is ideal for ‘dead DNA’
• Only 6% of DNA extracted from Neanderthal fossils belongs to
• FOXP2 gene and human spoken language: insights from comparative genomics and studies of human disease
Evolution of complex
spoken language
• Evolved in ancestral
Homo sapiens population
in Africa
• Enabled greater
integration within social
groups, more complex
culture and more
efficient cultural
• Provided competitive
edge in competition with
A. Structure of FOXP2 gene showing mutations that cause verbal dyspraxia
B. Phylogenetic analysis indicating high rate of amino acid substitution in human
FOXP2 since divergence from human-chimp ancestor
C. Humans with verbal dyspraxia exhibit abnormality in brain function during
• Ethology versus psychology
• The study of animal behavior
in relation to the natural
• The ecology and evolution of
animal behavior
• Pioneering ethologists
– Konrad Lorenz, Niko Tinbergen
and Karl von Frisch
– first and only animal behaviorists
to win Nobel prize (in physiology
and medicine, 1973)
• The study of how behavior is
modified by experience through
learning and memory
• Proximate questions versus ultimate questions
• How Questions = Proximate Questions
– What are the mechanisms underlying behavior?
– How is the nervous system wired?
– What stimuli elicit a behavior?
– How do hormonal levels influence the development and expression of the
• Why Questions = Ultimate Questions = Evolutionary Questions
– What is the purpose or function of a behavior?
– How does the behavior affect the probability of survival and/or
reproduction of an individual?
– What was the original step in the historical process that led to the
existence of a behavior?
– How has the behavior evolved and how has it changed over evolutionary
• Instinctive behavior = Fixed action pattern = innate behavior
Instinctive behaviors
• Behaviors that appear in fully
functional form the first time they
are performed
– term “genetically-determined” is
somewhat misleading
• Called Fixed action patterns (FAPs)
by ethologists
– web-building in spiders
– egg-rolling in geese
– pecking response in gull chicks
• Learned behaviors
• Involve the durable modification of
behavior in response to experience
• Testis-determining factor (TDF): effects on male brain development and behavior
Primary sex-determining
signal stems from testis
determining factor
(TDF) on Y
• Organizational effect
– affects development of
brain when the animal is
very young
• Activational effect
– high concentration of
hormone triggers sexual
• Estrogens, estradiol
• In absence of TDF,
ovaries develop and
testes regress
• Female fetus develops
under the influence of
estrogens (estradiol)
• Brain develops
estrogen receptors
• Maturing brain
develops mechanisms
for mating and
maternal behavior
• Intrauterine position effects on male behavior
• Rats are multiparous
• Gender of neighboring
fetuses influences uterine
• 2M males
– male fetus develops between
two brothers
– low estradiol
• 0M males
– male fetus develops between
two sisters
– high estradiol
• Genetically identical 2M
males much more aggressive
that 0M males
• Deprivation experiments as tools for studying instinctive versus learned behavior
Many studies in
– rear individuals in
isolation to see if they
still exhibit the
• Alarm call versus contact call in galah parrots reared by pink cockatoos
• Both species nest in tree holes in Australia
• Sometimes larger cockatoos eject adult galahs
from nest after galahs have laid eggs
• Cockatoos become foster parents of galah
• Provides natural experiment to investigate
instinctive versus learned behaviors
• Galah chicks learn contact call of cockatoos
• By contrast, galah chicks give galah alarm and
begging calls despite having been completely
isolated from other galahs
• Twin concordance studies: identical twin versus fraternal twin comparisons
• Concordance: presence of a
given trait in both members of a
pair of twins
• If genes influence probability of
exhibiting a trait, identical twin
pairs will be highly concordant
• Fraternal twin pairs
– no more similar genetically than
non-twin siblings
– less concordant - more pairs in
which one twin exhibits the trait
and other does not
• Comparison of degree of
concordance in identical and
fraternal twins provides estimate
of extent to which genes
influence trait expression
• Cognitive and
personality traits
influenced by both
genes and the
• Heritability of
behavioral traits
similar to that of
cardiovascular risk
• However, most
complex behaviors
influenced by many
• Reverse genetics
Classical genetics
• Observe phenotype
• Infer genetic basis from breeding experiments or twin studies
Reverse Genetics
• Manipulate gene
– insert genetically engineered mutant version of gene
– silence gene by interference RNA or similar method
• Examine phenotypic consequences of genetic manipulation
• fruitless gene and male courtship in Drosophila
Male courtship
• Requires products of fruitless (fru)
• Gene spliced differently in males and
• Alleles of fru constructed so male
splicing pattern occurs in both sexes
• Male splicing essential for male
courtship behavior and sexual
• Male splicing also sufficient to
generate male behavior in otherwise
normal females
• Splicing of single neuronal gene thus
specifies essentially all aspects of
complex innate behavior: Cell, 121:
785–794 (2005)
• Factors favoring instinctive over learned behaviors
• Short generation time
and absence of parental
– insects, spiders, etc.
– no time for learning
• Expression of behavior is
appropriate in almost
every context
– pecking response is "feed
• Expression of behavior
has to be right the first
– alarm calls
– predator avoidance in
kangaroo rats
• Releasers (and examples)
Releaser: specific stimulus
required to elicit a FAP
• Red underside acts as
releaser of male aggressive
behavior in sticklebacks
– realistic stickleback model
without red elicits no
– any of models with red
underside elicit strong
aggressive response
• Red bill spot in gulls
– only a red spot on an
elongate rod is needed to
elicit pecking response in
• Super-releasers in brood parasites
Duped by a super-releaser
• Cuckoos are brood
parasites on several bird
species including reed
• Female cuckoo lays eggs in
nest of host species
• Cuckoo chick hatches first
and literally kicks out eggs
of host species
• Gaping beak of
comparatively huge cuckoo
acts as super-releaser of
feeding behavior in reed
warbler adoptive parent
• Instinctive behaviors in humans: smiling, flirtatious behavior and eyebrow flash
Study of possible FAPs pioneered by German
ethologist, Irenaeus Eibl-Eibesfeldt
• Filmed people across range of cultures with right-angle
reflex lens camera
• Human universals: smiling, flirtatious behavior and the
“eyebrow flash”
• What is learning?
Learning: the durable modification of
behavior in response to experience
• Classical conditioning
Studied by Pavlov
• Involuntary activity becomes
associated with stimulus
• Animal learns to associate
involuntary activity with stimulus
• Repeated association of stimulus
with reward or punishment causes
stimulus alone to elicit response
• Turn on light, give dog meat
powder, dog salivates
• Eventually light alone causes dog to
• Occurs in organisms ranging from
roundworms to humans
• Operant conditioning (trial and error learning)
Animal learns to associate voluntary behavior with a stimulus
• Trial and error learning
• Skinner boxes
• Skinner box
Contains one or more levers which
animal can press
• One or more stimulus lights and one
or more places in which
reinforcement stimuli such as food
can be delivered
• Presses on levers can be detected and
recorded and delivery of
reinforcement can be set up to operate
• Also possible to deliver other
reinforcement stimuli such as water
• Or to deliver punishment such as
electric shock through the floor of the
B.F. Skinner: an evil mad scientist?
Thought much of human behavior could be
reduced to operant conditioning
• Skinner raised own daughter (Deborah)
in a "Skinner box”
• As a result, she grew up psychologically
damaged, sued her father, and
committed suicide
• Constructed crib similar to large hospital
incubator - tall box with door at base
and a glass window in front
• “Baby tender" provided Deborah with
place to sleep without need for layers of
clothing and blankets
• Deborah slept in baby tender until two
and a half years old and grew up a
healthy child
• Behavioral imprinting
Behavioral imprinting
• Pioneered by Konrad Lorenz
• Form of learning in which individuals
exposed to certain key stimuli very
early in development form a lifelong
association with the object
• Imprinting and the domestication of the Paca
Paca (Agouti paca)
• One of largest rodents in the world
• Prized by hunters throughout Central
and South America
• Weighs up to 30 lbs and is “muy
Nick Smythe
• Former staff scientist at Smithsonian
Tropical Research Institute in
• Paca as ecologically friendly
alternative to cattle
• By imprinting newborns on large
social groups, able to domesticate
paca within just a few generations
• Population density, biomass and spacing
• Population density
– number of individuals of a species per
unit area (terrestrial)
– number of individuals of a species per
unit or volume (aquatic)
• Biomass
– total mass of all individuals of a species
– usually expressed per unit area or volume
– corrects for size differences between
• Spacing
– the distribution pattern of individuals
across space
• Clumped versus random versus uniform distribution
Patterns of spacing
• How individuals are distributed over
• Can provide insights into processes
that shape group structure
Three types of patterns
• Clumped (or aggregated)
– social behavior
– heterogeneous environment
• Uniform
– usually indicates intraspecific
• Random
– passive dispersal combined with
weak interactions between
– combined effects of environmental
heterogeneity and competition
• Population dynamics and demographic processes
Population dynamics
• Describes whether a
population is increasing,
decreasing or staying the
same size
• Depends on demographic
• Demographic Processes
– births
– deaths
– immigration
– emigration
• Exponential population growth (recognize equation, graph and know terms in equation)
• Asexually reproducing
organism that divides in
two every 20 min (e.g.,
E. coli)
• In technical terms, a
discrete generation, pure
birth process model of
population growth
Exponential growth
• occurs when birth rate and death rate do not change with
population size; assumes resources are unlimited
dN/dt = rate of population change
b = average birth rate per individual (per capita)
d = average death rate per individual (per capita)
N = number of individuals in population (= population size)
b-d = rmax
• r is called the "intrinsic rate of increase”
• per capita rate of population growth
If b > d, population will grow exponentially
• Carrying capacity
Carrying capacity (K)
• maximum number of individuals of a species that can be
supported by a particular environment
Population size is limited
• food
• nest sites
• disease
• predators
• social interactions
• Logistic population growth (recognize equation, graph and know terms)
S-shaped growth curve
• dN/dt = rate of population change
• N = population size
• r = per capita rate of population
growth (a constant)
• K = carrying capacity
• Density dependent versus density independent population regulation
Density dependent
• Per capita birth or death rate depends on the population
• Usually biotic factors
– increased competition for food or space
– increased risk of disease or predator attack
Density independent
• Per capita birth or death rate does not vary with density
• Usually abiotic factors
– hurricane induced mortality
– frost damage from cold spell
Equilibrium is
reached when birth
rate and death rate
are equal
If birth rate or death
rate or both are
density dependent,
fluctuates around an
equilibrium size,
the carrying
capacity (K)
• Maximum sustained yield
Maximum sustained yield
• Population size at which the harvest rate is
– occurs where dN/dt is at a maximum
• For the logistic curve
– occurs at the inflection point (K/2)
– that is, at half the carrying capacity
• Over-harvesting: consequences and examples
• reducing population levels below
• results in low harvest rate
• high probability of population
• has occurred with many fisheries
• Technical solution and tragedy of the commons
• Technical Solution
• one that requires change only in
techniques of natural sciences,
and no change in human values
or ideas of morality (Hardin
• Over-harvesting and human
population growth cannot be
addressed with a technical
The collapse of California’s sardine
industry, once the largest fishery in
the world, was triggered by overharvesting
Over-harvesting of whales
• Sequential over-harvesting of whale species has
driven several them to the brink of extinction
• Classic example of Tragedy of the Commons
• How do we calculate doubling time?
ln 2= rt
t = ln2/r = 0.693/r
• Human population growth: birth versus death rate control
I. Decrease birth rate
• Natural controls
– Low food supply inhibits pregnancy
or increases risk of spontaneous
• Voluntary family planning
– Abstinence
– Rhythm method
– Artificial contraception
– Abortion
• Involuntary family planning
– Restrictions or fines limiting
reproduction, e.g., China
– Forced sterilization
II. Increase death rate
Natural Controls
• Infectious disease
 40% of young adult population HIV
positive in some African countries
• Mass starvation
– Ethiopia, Somalia
• Nazi Germany, Liberia,
Cambodia, Rwanda, Darfur
• Demographic transition
In industrialized societies
• changing roles of women
in society resulted in
natural decline in birth
rate in association with a
decline in death rate
In developing countries
• public health measures
result in rapid decline in
death rate without
concomitantly rapid
decline in birth rate
• Life history, life table and cohort
• Life History
– the stages of growth, reproduction and dispersal that an individual passes through during its
life from birth to death
• Life Tables
– summarize the schedule of births, deaths and reproduction through the life history of an
• Cohort
– a group of individuals born at the same time
– used to calculate life tables
• Semelparity versus iteroparity
Semelparity is reproductive event only at one point in time. Iteroparity is both seasonal and continuous reproductive events.
• Type I, II and III survivorship curves
• Note: Y-axis (number surviving) is on log-scale
• Type 1: nearly all individuals survive potential life span then die almost simultaneously
– annual plants
– semelparous, big bang reproducers
– approximated by human populations in industrialized societies
• Type 2: constant survivorship throughout life span
– song birds
• Type 3: survivorship very low for young individuals but high for adults
– marine organisms with planktonic larvae, e.g., oysters
• Ageing versus senescence
• Ageing
– all time-dependent changes that occur in molecules,
cells and tissues of an organism
• Senescence
– progressive loss of function accompanied by
decreasing fertility and increasing mortality with
advancing age
– subset of aging-related changes that negatively affect
the functions of an organism
• How can life history theory explain aging?
– Force of natural selection declines with age and late-onset diseases have been invisible to
selection throughout much of human evolution.
Early (incorrect) evolutionary explanations for aging
• Senescence is programmed in
order to limit population size or
accelerate turnover of
populations, thereby aiding
adaptation to changing
environments (altruism, group
• Flaw in argument
– Scant evidence that senescence
contributes significantly to
mortality in the wild
Extrinsic mortality in wild environments
occurs to an extent that senescentassociated
mortality is rare, undermining
idea that genes specifically for aging have

Evolutionary explanations for senescence
I: Mutation/selection balance
• Genetic variation maintained
by balance between
– input of variation from mutation
at many loci, and
– loss of variation due to selection
• Because selection is weaker at
older ages, there is higher
equilibrium level of
deleterious mutations that
exert their effects at later ages
compared to mutations that
exert their effects early in life

Evidence for mutation/selection balance
• Adaptations that reduce extrinsic
mortality (e.g., wings, shells,
large brains) are linked to
increased longevity
• Aging should occur more rapidly
in hazardous environments
• Populations of opossums on
mainland versus islands
– On mainland, predation is
 aging is faster
– On islands, predation much
 aging is slower

Evolutionary explanations for senescence II.
Antagonistic pleiotropy theory
• Senescence occurs because of
pleiotropic effects of genes
• Selection for alleles that enhance
survivorship and/or reproduction
at early ages may simultaneously
lower survivorship and
reproduction at later ages
• There is a tradeoff (antagonism)
between fitness components early
in life and later in life
• Because contribution to fitness
depends on both strength of gene
effect and probability of surviving
to be affected, small beneficial
effect early in life outweighs
large, deleterious effect late in life

Evidence for Antagonistic Pleiotropy
• Protein p53 is a tumor
suppressor gene that
restrains uncontrolled
growth in cancer
• P53 mediates trade-off
between cancer risk and
rate of aging
a. p53 +/+ mouse (wild-type)
• High cancer
• Slow aging
b. p53 +/m mouse (p53 overexpressed)
• Low cancer
• Rapid aging
• Types of species interactions:
competition, predator/prey
parasitoid/host, parasite/host and mutualism
• Resource/exploitation competition versus interference competition
Resource competition = Exploitation competition
• Two or more species
exploit same limiting
– food, nest sites, settling
space in rocky intertidal
• Each species depresses
population growth rate of
the other
• Ecological niche
– ecological role of a species
in a community
– range of physical conditions
and resources required by a
• Ecological niche: fundamental versus realized niche
Fundamental niche
• an n-dimensional
hypervolume describing
range of physical
conditions that can be
occupied by a species
Realized niche
• subset of fundamental
niche that is actually
occupied in presence of
other species including
predators and competitors

Fundamental and realized niches in barnacles
• Intertidal zone is an ideal environment for studying relationship between
fundamental and realized niche
• Characterized by steep environmental gradients
• The barnacle, Chthamalus, occupies only small subset of its fundamental
niche due to presence of Semibalanus
• Gause’s Competitive Exclusion Principle
• Competitive exclusion principle
– no two species can occupy the
same ecological niche
– in a homogeneous environment,
one species always drives the
other to extinction
• Based on experiments with
Paramecium aurelia and P.

Gause showed that competitive
coexistence could be maintained in
heterogeneous environments in which
each species does better than the other
in one of the “sub-environments”
• Competitive coexistence: environmental heterogeneity and disturbance
(biotic and abiotic)
• Paramecium aurelia and
P. caudatum both
predators on yeast and
• Both species grew well
in culture tubes by
themselves and
exhibited logistic growth
• When grown together,
P. caudatum always
declined to extinction
• Concluded that no two
species with same niche
can coexist when
resources are limiting
• How does environmental heterogeneity enable competitive coexistence
between Chthamalus and Semibalanus?
In nature, competitive coexistence is
achieved by
• Environmental heterogeneity
– natural selection favors resource partitioning
• Disturbance or predation
– prevents competitive exclusion by restricting
population growth of the competitively
dominant species

• Semibalanus is distributed over a broad range of depths but is more
sensitive to desiccation
• Chthamalus is more desiccation tolerant but is out-competed by
Semibalanus lower in the intertidal zone
• Resource partitioning, character displacement and ecological release
Resource partitioning
• dividing of scarce resources so that
species with similar requirements can
use resources in different ways, in
different places, and at different times
• the ghost of competition past
• indirect evidence of earlier competition
resolved by evolution of niche
Anolis lizards on Caribbean islands
a. Canopy species
b. Twigs on periphery
c. Base of trunk
d. Open, grassy areas on ground

Character displacement
• Tendency for
characteristics to be more
divergent in sympatric
populations of two species
than in allopatric
populations of the same
two species
Ecological release
• a species expands its
resource use when a
competitor species is absent
• Correlative versus experimental evidence for competition
Most direct method of assessing
• Remove individuals of species A
and measure response of species
• Removal treatments easy to carry
out on sessile species
• Connell’s hypothesis
– Chthamalus competitively
excluded from lower intertidal by
• Transplanted rocks from high
intertidal to low intertidal
• Experimentally removed
Semibalanus from one side of
rock and left other side as control
• Monitored survival of
Chthamalus on both sides of
• Predator-mediated coexistence and keystone species: Pisaster example
• Sea star (Pisaster) is
predator of mussels
(Mytilus californianus)
• Mussels are competitive
dominant species along
rocky shores of Pacific
• In absence of Pisaster,
mussels monopolize space
• Pisaster lowers
population density of
Mytilus, preventing
competitive exclusion
• Pisaster is keystone
• Interference competition: examples
• One species directly
interferes with another to
prevent it from using a
• Lions kill cheetah cubs
but don’t eat them
• Lions kill hyenas but
don’t eat them
• Common in sessile
marine invertebrates that
compete for space
– anemones sting each other
– corals chemically digest
their competitors
• Predator/prey versus parasitoid/host versus parasite/host
One species benefits, other
is harmed
• Predator/Prey: predator
benefits, prey is harmed
• True predation: predator
kills prey in a single act
• Predator/prey interactions
characterized by
oscillations in
predator/prey numbers

Parasitoid/host and parasite/host
Again, one species benefits, other is
• Parasitoid/host: larvae of parasitoid
slowly consume host and kill it
– 60,000 species of parasitoid wasps in
family Ichneumonidae
– Cotesia congregata injects both eggs
and polydnavirus into host, the
tobacco hornworm
– virus causes host immunosuppression,
allowing parasitoids to mature without
invoking strong host immune response
• Parasite/host: parasite garners
resources from host but doesn't
necessarily kill host
• Mutualism: examples
Both species benefit from the
• Flowering plants and animal
• Corals and zooxanthellae
• Ruminants (cows, sheep,
goats, etc.) and
endosymbiotic bacteria
– mutualism enables digestion of
• Termites and intestinal
• Mimicry: Mullerian versus Batesian mimicry
Mullerian mimicry
• Similarity in appearance
between two or more
distantly-related noxious or
dangerous species
• Both species benefit from
this convergent similarity
Batesian mimicry
• Form of mimicry in which
an innocuous mimic species
gains protection by
resembling noxious or
dangerous model species
• Mimic species benefits
• Model species may be
slightly harmed
• Biodiversity
Biodiversity: biological
diversity at the level of the
• Gene
• Population/species
• Community/Ecosystem
• Conservation biology
• Goal is to understand causes
and consequences of
biodiversity in order to
develop scientifically-sound
principles for maximizing its
• Mutational meltdown/extinction vortex
• Selection not strong
enough to override
genetic drift in
small populations
• Evolutionarily significant unit (ESU): 3 definitions
The agony of choice
• More biodiversity for the dollar
Evolutionarily significant unit (ESU)
• A unique group of organisms that should be managed
• A population reproductively isolated from other conspecific
population units and representing an important evolutionary
legacy of the species
• Reciprocally monophyletic
• ESU should be reciprocally monophyletic for mitochondrial
– all alleles in each population genealogically closer to one another
than to any alleles in the other population
• Dusky Seaside Sparrow: lessons from molecular systematics
• Dusky Ammodramus maritimus
nigrescens was phenotypically
divergent from other subspecies
- darker head and back
• Faced with extinction due to loss
of wetland habitat in NE Florida
• Last two males crossed with
females from Gulf coast
subspecies (A. m. peninsulae)
– crosses unsuccessful
• Post-extinction mitochondrial
DNA sequencing revealed that
– Dusky differed little from other
Atlantic coast subspecies
– subspecies A. m. peninsulae
geographically close but
genetically very different
• Two views of the Tropics
• Tropics as a
fascinating repository
of biological diversity
– Charles Darwin on the
– Alfred Russell Wallace
on the Tropics
• Tropics as a hostile
and dangerous place
that should be tamed
and exploited for
human development
– Beyond the Chagres
• Where are tropical rain forests?
• 6% of land surface or about 8.5 million km2
• About 2/3 of rain forest area in South America (Amazonia); remainder in Asia
(Indonesia and New Guinea) and Africa (Congo Basin & Zaire)
• High productivity
• Rapid decomposition
• Low volume of nutrients in soil
• Acidic soils
• Seasonality and distance from the equator in tropical rain forests
• French Guiana
– 40 N latitude
– 2.5 month continuous dry
• Panama
– 90 N
– 4 month continuous dry
• Belize
– 150 N
– 5 month continuous dry
• Tropical forest types: how defined and which is most and which is least diverse?
Lowland Forest
• To 1000 m elevation
• Canopy height 45 m
• Highest total diversity
Montane forest
• 1000 m to 3000 m elevation
• Canopy 2 to 15 m
• Abundant epiphytes
• Estuarine
• Low diversity but high productivity
• Most genera distributed worldwide
Flooded Forests of the Amazon
• Terrestrial communities submerged
for much of rainy season
• Soil instability favors stilt roots and
flying buttresses
• Fish important in seed dispersal
• Harsh conditions and low species