Human Evolution Textbook notes for Midterm (Chapters 1-9)

7/29/2019 Human Evolution Textbook notes for Midterm (Chapters 1-9)

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Human Evolution Textbook Notes

by Bridget Walsh

Chapter 1: Adaptation by Natural Selection

Explaining adaptation before Darwin- animals and plants are adapted to their conditions in subtle and marvelous ways

- adaptation: feature of an organism created by the process of natural selection

- human eye: like a camera lens, light is bent when it passes through the air to then pass

through the cornea restricting how it can function unlike fish eyes (eyes in water

animals), because light does not bend in the same way in water, fish eyes can see 180

degrees in water

- before darwin there was no scientific explanation for the fact that organisms are well adapted to

their circumstances

- used to believe adaptation were the result of divine creation

- rather than random changes over a long period of timeDarwins Theory of adaptation

- Charles Darwin was expected to become a doctor or clergyman, but instead he revolutionized

science

- intellectual family, didnt very well in school

- university of Edinburgh and Cambridge university

- went on the Beagle, which was sent to map south america

- observations on this trip crucial

- Darwins Postulates

- darwins theory of adaptation follows from three postulates: (1) the struggle for existence, (2)

variation in fitness (3) the inheritance of variation- 1. the ability of a population to expand is infinite but the ability of any environment to

support populations is always finite

- 2. organisms within populations vary, and this variation affects the ability of individuals

to survive and reproduce

- 3. this variation is transmitted from parents to offspring

- grown until they are checked by environment coined the term natural selection

- An example of adaptation by Natural Selection

- contemporary observations of Darwins finches provide a particularly good example of how

natural selection produces adaptations

- Grants, biologists at Princeton

- ground finch in the Galapagos, few years in a severe drought struck

- finches with larger beaks were favored because the smaller seeds that smaller beaks

thrived on were affected by drought

- this shifted the average beak size of the population as the population decreased under

environmental strain

- The Grants data show how that processes identified in Darwins postulates lead to adaptation


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- 1. struggle for existence + environment could not support large population of finches

due to drought

- 2. variation favored larger beaks

- 3. larger beaks were more likely to reproduce

- changed the morphology [form and structure of an organism]

- selection preserves the status quo when the most common type is the best adapted- stabilizing selection [selection pressures that favor the average phenotypes. alters the

amount of variation but not the mean value of the trait]

- evolution need not always lead to change in the same direction

- natural selection has not foresight-->random

- species are populations of varied individuals that may or may not change through time

- species is not a fixed type or entity

- species change in their general characteristics

- the characteristics of a species will be static over time is stabilizing selection is

consistently favored, statis is not the natural state of a species

- Individual Selection- adaptation results from the competition among individuals, not between entire populations or

species

- selection often leads to changes that will increase the reproductive success of

individuals but decrease average reproductive success of the group, population or

species

- The Evolution of Complex Adaptations

- Why Small Variants Matter

- there are two categories of variation: continuous and discontinuous

- continuous variation: phenotypic variation in which there is a continuum of types-->heights in humans

- discontinuous variation: phenotypic variation in which there are distinct types and no

intermediary types--> Mendels pea plants

- discontinuous variation is not important for the evolution of complex adaptations because

complex adaptations are extremely unlikely to arise in a single jump

- probability of monkeys typing a line of shakespeare

- complex adaptations can arise through the accumulation of small random variations by natural

selection

- with a bit of selection evolution happens faster--> environmental pressures

- Why Intermediate Steps are favored by Selection

- the evolution of complex adaptations requires all of the intermediate steps to be favored by

selection

- tinkerer not an engineer

- 5% of an eye is better than 0%

- sometimes unrelated species have independently evolved the same complex adaptation,

suggesting that the evolution of complex adaptations by natural selection is not a matter of

mere chance


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- convergence: the evolution of similar adaptations in unrelated species. the evolution of

camera like eyes in both vertebrates and mollusks is an example of convergence

- Rates of Evolutionary Change

- natural selection can cause evolutionary change that is much more rapid than we commonly

observe in the fossil record

- there is enough time for evolution, not as slow as you think- artificial selection with dog breeds shows us this as there are many breeds within 200

years of breeding

- incomplete fossil record inhibits our estimates

- Darwins Difficulties Explaining Variation

- Darwin couldnt convince his contemporaries that evolution occurred through the accumulation

of small variations because he couldnt explain how variation is maintained

- didnt understand inheritance, study of genetics not adequately developed

- believed in the blending hypothesis

- totally wrong, easily disproved

Chapter 2: Genetics

Mendelian Genetics

- By conducting careful experiments with plants Mendel discovered how inheritance works

- isolated traits [variants]

- performed crosses of pure breeds

- F0 [initial], F1, F2 are successive generations

- Mendel was able to formulate two principles that accounted for his experimental results

- 1. The observed characteristics of organisms are determined jointly by two particles,

one inherited from the mother and one from the father. [genes]- 2. Each of these two particles [genes] is equally likely to be transmitted when gametes

are formed. modern scientists call this independent assortment

- Cell division and the role of chromosomes in inheritance

- nobody paid any attention to Mendels results for almost 40 years

- was an obscure monk in Slovakia

- when Mendels results were rediscovered, they were widely accepted because scientists now

understood the role of chromosomes in the formation of gametes

- chromosome: linear body in the cell nucleus that appears during cell division

- Mitosis and Meiosis

- ordinary cell division called mitosis creates two copies of the chromosomes present in the

nucleus

- nucleus: brain contains chromosomes

- in diploid organisms chromosomes come in homologous pairs

- in meiosis, the special cell division process that produces gametes, only half of the

chromosomes are transmitted from parent cell to the gamete

- cells that contain only one copy of each chromosome are haploid

- haploid sperm and haploid egg combine to form a diploid zygote


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- Chromosomes and Mendels Experimental Results

- Mendels two principles can be deduced from the assumption that genes are carried on

chromosomes

- one gene inherited from each parent and each gene is equally likely to be transmitted

- different varieties of a particular gene are called alleles. Individuals with two copies of the same

allele are homozygous; individuals with different alleles are heterozygous- a cross between a homozygous dominant parent and a homozygous recessive parent produces

all heterozygotes in the F1 generation

- a cross between heterozygous parents produce a predictable mixture of all three genotypes

- punnet squares

- Linkage and Recombination

- Mendel also performed experiments involving two traits that he believed showed that separate

characters segregate independently

- recombination [the creation of novel genotypes as a result of the random segregation of

chromosomes and crossing over]

- genes are arranged on chromosomes like beads on a string- occur at a particular site called a locus

- all of the genes carried on all the chromosomes is called the genome

- traits may not segregate independently if they are affected by genes on the same chromosome

- same chromosome said to be linked

- loci on different chromosomes said to be unlinked

- breaks up in the process and some degree ofcrossing over occurs

- Molecular Genetics

- genes are segments of a long molecule called DNA, which is contained in chromosomes

- understanding the chemical nature of the gene is critical to the study of human evolution: (1)

molecular genetics links biology to chemistry and physics and (2) molecular methods help usreconstruct the evolutionary history of human lineage

- Genes are DNA

- DNA is unusually well suited to be the chemical basis of inheritance

- base pairs: ATCG

- the message encoded in DNA affects phenotypes in several different ways

- 1. DNA in protein coding genes specifies structure [enzymes]

- 2. DNA in regulatory genes determines the conditions under which the message

encoded will be expressed

- 3. RNA

- Some genes code for proteins

- proteins called enzymes influence an organisms biochemistry

- biochemical pathways

- proteins play a number of other important roles in the machinery of life

- keratin

- collagen

- the sequence of amino acids in proteins determines their properties

- sequence of side chains is primary structure


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- folding is tertiary structure

- DNA specifies the primary structure

- codons

- before DNA is translated into proteins, its message is first transcribed into messenger RNA

- the ribosome then synthesize a particular protein by reading the mRNA copy of the gene

- tRNA has an anticodon- in eukaryotes, the DNA that codes for proteins is interrupted by noncoding sequences called

introns

- removed and then join exons together

- alternative splicing allows the same DNA sequence to code for more than one protein

- Regulatory Sequences control gene expression

- the DNA sequence in regulatory genes determines when protein coding genes are expressed

- lactose metabolism in e.coli

- repressor and activators

- gene regulation allows cell differentiation in complex multicellular organisms like humans

- Not all DNA carries a message- some DNA sequences code for functional RNA molecules

- microRNA [epigenome]

- chromosomes also contain long strings of simple repeated sequences

Chapter 3: The Modern Synthesis

- Population Genetics

- evolutionary change in a phenotype reflects change in the underlying genetic composition of

the population

- Genes in Populations- biologists describe the genetic composition of a population by specifying the frequency of

alternative genotypes

- fraction of the population that carry a specific genotype

- one goal of evolutionary theory is to determine how genotypic frequencies change through time

- sexual reproduction, mutation, genetic drift, natural selection

- How random mating and sexual reproduction change genotypic frequencies

- the events that occur during sexual reproduction can lead to changes in genotypic frequencies

in a population

- first step is to calculate the frequency of an allele in the pool of gametes

- q=frq(aa) + 0.5 x freq(Aa)

- next step is to calculate the frequencies of all genotypes among the zygotes

- event tree

- when no other forces (such as natural selection) are operating, genotypic frequencies reach

stable proportions in just one generation. these proportions are called the Hardy-Weinberg

equilibrium

- How natural selection changes gene frequencies


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- if different genotypes are associated with different phenotypes and those phenotypes differ in

their ability to reproduce, then the alleles that lead to the development of the favored phenotype

will increase the frequency

- selection cannot produce change without variation. if all the individuals were

homozygous for the normal allele, gene frequencies would not change from one

generation to the next- selection does not operate directly on genes and does not change the gene frequency

directly. instead, natural selection changes the frequency of different phenotypes

- the strength and direction of selection depend on the environment

- The modern synthesis

- The Genetics of Continuous Variation

- when Mendelian genetics was rediscovered, biologists thought it was incompatible with

Darwins theory of evolution by natural selection

- believed that discontinuous evolution was the way change happened

- Mendelian genetics and Darwinism we eventually reconciled, resulting in a body of theory that

solved the problem of explaining how variation is maintained- modern synthesis

- continuously varying characters are affected by genes at many loci, each locus having only a

small effect on phenotype

- if there are two types of beak depth (deep and shallow) plus an intermediary--this does

not look like a smooth bell curve of beak depths like in nature

- 1. phenotypic expression of all characters, whether affected by one locus or many

depends on the environment

- Darwins view of natural selection is easily incorporated into the genetic view that evolution

typically results from changes in gene frequencies

How variation is maintained- genetics provides a ready explanation for why the phenotypes of offspring tend to be

intermediate between those of their parents

- there is no blending of genes during sexual reproduction

- mutation slowly adds new variation

- introduce new alleles

- low mutation rates can maintain variation because a lot of variation is protected from selection

- when a large number of loci affect the expression of a trait, only a fraction of the

variation present is expressed phenotypically

- hidden variation explains why selection can move populations far beyond their initial range of

variation

- Jenkins: evolution could not account for long term changes because it could never

change the finches beak larger than the initial largest beak

- Jenkins argument is wrong because didnt take hidden variation into account

Natural Selection and Behaviour

- the evolution of mate guarding in the soapberry bug illustrates how flexible behaviour can

evolve


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- behaviour is different from morphology because it is flexible and can be adjusted

according to circumstance

- male guarding: stays in the copulatory position for hours to increase his reproductive

success and prevent her from copulating with other males before she lays her eggs

- depends on the sex ratio

- behavioural plasticity allows male soapberry bugs to vary their male guarding adaptivity inresponse to variation in the local abundance

- if the trait is canalized [same phenotype in in a wide range of environments] then a male

would behave the same way in regardless of sex ratio

- if the trait is plastic then the male will adjust behaviour

- evidence suggests that the soapberry bugs plasticity has evolved in response to the variability

in conditions in Oklahoma

- behavioural plasticity evolves when the nature of the behavioural response to the environment

is genetically variable

- character must vary

- the variation must affect reproductive success- and variation must be heritable

Constraints on adaptation

- Correlated characters

- when individuals that have particular variants of one character also tend to have particular

variants of a second character, the two characters are said to be correlated

- positively or negatively

- correlated characters occur because some genes affect more than one character

- pleiotropic effects: genes that effect more than one character

- when two characters are correlated, selection that changes the mean value of the correlatedcharacter

- correlated response: evolutionary change in one character because of a change in

another

- a correlated response to selection can cause other characters to change in a maladaptive

direction

- maladaptive: lower reproductive fitness

- Disequilibrium

- selection produces optimal adaptations only at equilibrium

- disequilibrium is especially evident in humans as we have undergone massive changes

in 10,000 years

- e.g. our diet, used to have an insatiable appetite for salt and fat now that these are

abundant this adaptation can lead to health problems such as diabetes and obesity

- Genetic Drift

- when populations are small, genetic drift may cause random changes in gene frequencies

- sampling variation: the variation in the composition of small samples from a large

population


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- genetic drift: random changes in gene frequency due to a sampling variation

- imagine a large urn with equal amount of black and red marbles, there are also 5 smaller

urns which you fill with marbles from the large urn at random. Therefore each smaller

urn with have a random distribution of red and black marbles--not necessarily equal

amounts as in the large urn. This analogy illustrates how small populations can have

different gene frequencies of a specific allele.- the rate of genetic drift depends on population size

- more rapid change in small populations

- genetic drift causes isolated populations to become genetically different from each other

- until a population reached fixation [all individuals are homozygous for the same allele

in a particular locus]

- species may die before fixation occurs (especially large populations)

- Locus versus optimal adaptations

- natural selection may lead to an evolutionary equilibrium at which the most common phenotype

is not the best possible phenotype

- myopic because: selection favors small changes, does not consider long run benefits/faults

- e.g. humans and other vertebrates have a camera-like eye whereas flies have compound

eyes (many small areas of focus). camera-like is better is most situations, but once a

complex compound eye has evolved it is much harder for a camera like eye to evolve

- some local adaptations are called developmental constraints

- process of growth and differentiation called development

- developmental changes that would be advantageous sometimes are not selected for

because alterations may have other negative effects

- Other Constraints on Evolution

- evolutionary processes are also constrained by the laws of physics and chemistry- e.g. laws of mechanics predict the strength of bones is proportional to their cross

sectional area--> constrains the evolution of morphology

- if an animals size doubles, then its weight increases by a factor of 8, the strength to bear

an animals weight comes from its muscles and bones and is largely determined by the

cross sectional area, therefore there is a trade off between size and agility

Chapter 4: Speciation and Phylogeny

What Are Species?

- microevolution refers to how populations change under the influence of natural selection and

other evolutionary forces; macroevolution refers to how new species and higher taxa are

created

- species can usually be distinguished by their behaviour and morphology

- concerned with why species exist and how they came about

The Biological Species Concept

- the biological species concept defines a species as a group of interbreeding organisms that are

reproductively isolated from other organisms


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- reproductive isolation: members of a given group do not mate successfully with

members outside of said group

- gene flow: the movement of genetic material within parts of a population or from one

population to the next

- ability to interbreed leads to gene flow

- reproductive isolation prevents species from genetically blending- no hybrids

The Ecological Species Concept

- The ecological species concept emphasizes the role of selection in maintaining species

boundaries

- critics of the biological species concept contend that is neither necessary nor sufficient

to maintain species boundaries

- selection can favor different and distinct features and not the intermediary forms

(hybrids typically have lower fitness)

The Origin of Species

- speciation is difficult to study empirically- macroevolution takes too long for one individual to observe, and too fast for the fossil

record

Allopatric Speciation

- if geographic or environmental barriers isolate part of a population and selection favors

different phenotypes in these regions, then a new species may evolve

- character displacement: the result of competition between two species causes the two

to become more different from one another

- reinforcement: selection acting against hybrids, hybrids reduce viability

Parapatric and Sympatric Speciation

- new species may also form if there is strong selection that favors two different phenotypes- biological species advocates say that gene flow welds a species together

- parapatric speciation: selection alone is not enough to form a new species; selection

plus partial genetic isolation. species experience different environments in different

parts of its geographic range, natural selection causes these species to diverge and

eventually reproductive isolation is achieved.

- sympatric speciation: occurs when selection strongly favors different adaptations to a

similar environment within a single species

- adaptive radiation occurs when there are many empty niches

The Tree of Life

- organisms can be classified hierarchically on the basis of similarities . Many such similarities

are unrelated to adaptation

- speciation explains why organisms can be classified hierarchically

- species derive from existing species

- family tree orphylogeny

Why Reconstruct Phylogenies?

- phylogenic reconstruction plays three important roles in the study of organic evolution

- 1. phylogeny is the basis for the identification and classification of organisms


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- 2. knowing phylogenic relationships often helps explain why a species evolved certain

adaptations and not others

- 3. we can deduce the function of morphological features or behaviors by comparing the

traits of different species

- comparative method

- e.g. terrestrial vs. arboreal primates (living in groups vs. living alone)- taxonomy refers to naming, systematics refers to the construction of phylogenies

How to Reconstruct Phylogenies

- we reconstruct phylogenies on the assumption that species with many phenotypic similarities

are more closely related than species with fewer phenotypic similarities are.

Problems due to Convergence

- in constructing phylogenies, we must avoid basing decisions on characters that are similar

because of convergent evolution

- analogous: independently evolved similarities

- homologous: common ancestor

Problems due to Ancestral Characters- it is also important to ignore similarity based on ancestral characters, traits that also

characterized the common ancestor of the species being classified

- ancestral trait vs. derived trait

- the closer the last common ancestor the closer the relation between species

- systematists distinguish between ancestral and derived characters using the following criteria:

ancestral characters (1) appear earlier in organismal development (2) appear earlier in the fossil

record and (3) are seen in out groups

Using Genetic Distance Data to Date Phylogenetic Events

- genetic distance measures the overall genetic similarity of two species

- genetic distance data are often consistent with the hypothesis that genetic distance changes atan approximate constant rate

- molecular clock: the hypothesis that genetic change occurs at a constant rate and thus

can be used to measure the time elapsed since two species shared a common ancestor.

the molecular clock is based on observed regularities

- neutral theory: a theory postulating that genetic change is only caused by mutation and

genetic drift

- if the molecular clock hypothesis is correct then knowing the genetic distance between two

living species allows us to estimate how long ago the two lineages diverged

Taxonomy: Naming Names

- the hierarchical pattern of similarity created by evolution provides the basis for the way science

classifies and names organisms

- taxonomists disagree about whether overall similarity should also be used in classifying

organisms

- cladistic taxonomy: only patterns of descent matter

- evolutionary taxonomy: both patterns of descent and overall similarity

Chapter 5: Primate Diversity and Ecology


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Two Reasons to Study Primates

- closely related species share similar morphological features because they share a common

ancestor e.g. viviparity

- how evolution shapes adaptation in response to selective pressures

Primates Are Our Closest Relative- because humans and other primates share many characteristics, other primates provide valuable

insights about early humans

- we share many aspects of morphology, physiology and development

- e.g. developed vision and grasping hands and feet, extended period of juvenile

development, larger brains in relation to body size

primates are a diverse order

- diversity within the primate order helps us to understand how natural selection shapes

behaviour

- diurnal: active during daylight hours

- conspecifics: species actively defend their territory from incursions by other membersof their own species

- differences observed among closely related species are likely to represent adaptive

responses to specific ecological conditions

Features that define primates

- members of the primate order are characterized by a number of shared, derived characters, but

not all primates share all of these traits

- 1. big toe is opposable and hands are prehensile (ability to grasp)

- 2. nails instead of claws, tactile pads with fingerprints

- 3. locomotion is hind-limb dominated (hind limbs do most of the work, lower center of

gravity)- 4. unspecialized olfactory apparatus in diurnal

- 5. vision highly developed

- 6. females have smaller litters, gestation, longer juvenile development

- 7. larger brain

- 8. molars are unspecialized, 2 incisors, 1 canine, 3 premolars

- binocular stereoscopic vision: image from the two eyes overlap so both eyes perceive

the same image, and they perceive depth

- strepsirrhine: lemurs and lorises

- haplorrhine: tarsiers, monkeys and apes

- ^suborders

- if there is an essence of being a primate it is the progressive evolution of intelligence

as a way of life

primate biogeography

- primates are mainly restricted to tropical regions of the world

- continents of asia, africa and south america

- diverse set of habitats within this range

A taxonomy of living primates


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- strepsirrhini are generally nocturnal, well developed sense of smell, large eyes, move their ears

Primate Diversity

The Strepsirrhines

- the strepsirrhine primates are divided into two infraorders: lemuriformes and lorisiformes

The haplorrhines

- the suborder haplorrhini contains three infraorders: tarsiiformes, platyrrhini and catarrhini- the infraorder catarrhini contains the monkeys and apes of the old world and humans

- the superfamily Ceropithecoidea encompasses great diversity in social organization, ecological

specializations and biogeography

- colobine monkeys, bonobos, vervets

- the superfamily hominoidea includes two families of apes: hylobatidae (gibbons) and

hominidae (orangutans, gorillas, chimpanzees and humans)

Primate Ecology

The distribution of food

- food provides energy that is essential for growth, survival and reprodution

- total amount of energy that an animal requires depends of four components:- basal metabolism: rate at which an animal expends energy to maintain life when at rest

- active metabolism: depends on the size and how fast it moves

- growth rate: require more energy when growing

- reproductive effort: during pregnancy primate females require 25% more energy and

50% more during lactation

- a primates diet must satisfy the animals energy requirements, provide specific types of

nutrients, and minimize exposure to dangerous toxins

- vitamins and minerals

- fats and oil contain about twice the amount of energy as carbs

- water- secondary compounds: toxic chemical compounds produced in plants to prevent things

from eating the plant

- e.g. alkaloids pass through the stomach into various cells and disrupt normal metabolic

functions

- primates obtain nutrients from many different sources

- gum, plants, insects, fruit

- frugivore, folivore, insectivore, gummivore---> depends on habitat and adaptations

- the nature of dietary specializations and the challenge of foraging in tropical forests influence

ranging patterns

Activity Patterns

- primate activity patterns show regularity in seasonal and daily cycles

- proportion of time devoted to various activities influenced by ecological factors

Ranging Behavior

- all primates have home ranges, but only some species are territorial-- defending their home

range against incursions by other members of their species

- the two main functions suggested for territoriality are resource defense and mate defense


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- territoriality is beneficial because is protects valuable resources but costly because

animals must be constantly vigilant and ready to defend their territory

- when benefits outweigh the costs territoriality occurs

Predation

- predation is believed to be a significant source of mortality among primates, but direct evidence

of predation is difficult to obtain- difficult to observe, can study the predators instead of the prey

- primates have evolved an array of defenses against predators

- alarm calls for a variety of predators

- take cover, fight

primate sociality

- sociality has evolved in primates in response to ecological pressures. Social life has both costs

and benefits.

- primatologists are divided over whether feeding competition or predation is the primary factor

favoring sociality among primates

Primate conservation- many species of primates are in real danger of extinction in the wild

- the main threats to primates in the wild are (1) habitat destruction (2) hunting (3) disease (4)

live capture for trade for trade and export

- efforts to save endangered primate populations have met with some success

Chapter 6: Primate Mating Systems

-understanding the diverse reproductive strategies of nonhuman primates illuminates human

evolution because we share many elements of our reproductive physiology with other species of

primatesThe Language of Adaptive Explanations

- in evolutionary biology, the term strategy is used to refer to behavioural mechanisms that lead

to particular courses of behaviour in particular functional contexts such as foraging or

reproduction

- cost and benefit refer to the effect of particular behavioural strategies on reproductive success

- beneficial if they increase reproductive fitness and costly if they dont

The Evolution of Reproductive Strategies

- primate females always provide lots of care for their young, but males do so only in a few

species

- males do not care for their offspring (1) when they can easily use their resources to acquire

many additional matings or (2) when caring for their offspring would not appreciably increase

the offsprings fitness

- the mammalian reproductive system commits primate females to investing in their offspring

- females lactate, biologists think that the ability to lactate would make male primates

sterile

Reproductive Strategies of Females

- female primates invest heavily in each of their offspring


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- pregnancy and lactation are time consuming and energetically expensive, each infant

represents a substantial proportion of a females lifetime fitness--> vested interest

- a females reproductive success depends on her ability to obtain enough resources to support

herself and her offspring

Sources of Variation in Female Reproductive Performance

- very young and very old females do not reproduce as successfully as middle aged females- primiparous (first time) gorilla mothers have higher infant mortality rate

- longevity is a major source of variation in female fitness

- longer females live the more offspring they produce

- high ranking females tend to reproduce more successfully than do low-ranking females

- dominance hierarchies

- better access to resources

- the quality of social bonds may also influence female reproductive success

- higher levels of cortisol in females with no friends; cortisol relates to stress

Reproductive Trade-offs

- females must make a trade-off between the number of off-spring that they produce and thequality of care that they provide

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

- outcomes not usually favored by natural selection; peacock feather, red deers antlers

- sexual selection is often much stronger than ordinary natural selection

- there are two types of sexual selection: (1) intrasexual selection results from competition

among males and (2) intersexual selection results from female choice

Intrasexual Selection

- competition among males for access to females favors large bodies, large canine teeth, andother weapons that enhance male competitive ability

- the fact that sexual dimorphism is greater in primate species forming one-male, multi-female

groups than in pair-bonded species indicates that intrasexual selection is the likely cause of

sexual dimorphism in primates

- sexual dimorphism: differences between sexually mature males and females

- in multi-male, multi-female groups, where females mate with several males during a given

esterous period, sexual selection favors increased sperm production

- estrus: female is fertile

- social organization is associated with testis size

Male Reproductive Tactics

Investing Males

- pair bonding is generally associated with high levels of paternal investment

- male guarding

- in cooperatively breeding species, males invest heavily in offspring, but the reproductive

benefits to males are not clear

Male-male Competition in Groups without Pair- Bonds


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- in these kinds of groups, the reproductive success of males depends on their ability to gain

access to gain access to groups of unrelated females and to obtain matings with receptive

females

- males can reduce the costs of dispersal:

- before they leave their natal groups, they can scope out neighboring groups

when those groups are close by- transfer to groups that contain familiar males from their natal groups

- migrate together with peers

- in species that normally form one male groups, males compete actively to establish residence in

groups of females

- residence in one-male groups does not always ensure exclusive access to females

- for males in multi-male groups, conflict arises over group membership and access to receptive

females

- not easy to join a group

- mediated by dominance relationships that reflect male competitive abilities

Infanticide- Infanticide is a sexually selected male reproductive strategy

- sexual selection infanticide hypothesis: when a female monkey gives birth to an infant,

she nurses it for a number of months and does not become pregnant for a considerable

amount of time. after the death of an infant, however, lactation ends abruptly and

females resume cycling

- 1) infanticide would be associated with changes in male residence or status

- 2) males should kill infants whose deaths hasten their mothers resumption of cycling

- 3) males should kill other males infants and not their own

- 4) infanticidal males should achieve reproductive benefits

- Infanticide is sometimes a substantial source of mortality- females have evolved a battery of responses to infanticidal threats

- reduce certainty of paternity by mating a lot

- the threat of infanticide seems to influence the nature of male-female relationships in baboons

- friendships with males help stave off infanticide

Chapter 7: The Evolution of Cooperation

Altruism: A Puzzle

- perform altruistic behaviour that benefit others but at personal cost

- e.g. grooming, giving warning calls

Mutualism

- sometimes helping others benefits the actor as well as the recipient. Such behaviors are

mutualistic

- win-win proposition

- slacking, think of group projects where one person slacks; mutualism is most likely to

work in situations in which slacking isnt profitable for anyone

- coalitions; e.g. male baboons coalition to gain access to females


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The Problem with Group-Level Explanations

- altruistic behaviors cannot be favored by selection just because they are beneficial to the group

as a whole

- inference that what is good for the group will be favored by evolution because it

confuses the effect on the group with the effect on the actor

- if alarm call monkey dies then his altruistic behaviour will not be passed on to asuccessive generation

Kin Selection

- natural selection can favor altruistic behaviour if altruistic individuals are more likely to

interact with each other than chance alone would dictate

- WD Hamiltons insight: any process that facilitates altruists to be more likely to interact

with other altruists could facilitate the evolution of altruistic behaviour

- altruist gives warning call to other altruists

- known as Hamiltons rule

Hamiltons Rule

- Hamiltons rule predicts that altruistic behaviour will be favored by selection if the costs ofperforming the behaviour are less than the benefits discounted by the coefficient between actor

and recipient

- rb>c

- r= the average coefficient of relatedness between the actor and the recipients

- b= the sum of the fitness benefits to all individuals affected by the behaviour

- c= the fitness cost to the individual performing the behaviour

- Hamiltons rule leads to two important insights: (1) altruism is limited to kin, and (2) closer

kinship facilitates more costly altruism

Kin Recognition- primates may use contextual cues to recognize maternal relatives

- smell or likeness, called phenotypic matching

- context: familiarity or proximity

- spend a lot of time with mother, time to observe her interacting with brother and sisters

- contextual cues may play some role in paternal kin recognition as well

- age might act as a contextual cue

- didnt think primates could recognize paternal siblings due to lack of pair bonding

Kin Biases in Behaviour

- grooming is also more common among kin than non-kin

- establishes affiliative contact; reinforce social relationships

- primates most often form coalitions with close kin

- taking greater risks on behalf of kin

- kin based support in conflicts affects the social structure of macaque, vervet and baboon groups

- maternal rank is transferred to daughters

- maternal kin occupy adjacent ranks in dominance hierarchy

- predictable and remarkable stable over time


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- kin based support plays an important role in the reproductive strategies of red howler males

- collective defense is crucial, only one or two males with a group of females

- kin selection plays an important role in cooperatively breeding primate groups

- breeding helpers

- chimeras

- rare but occurs in marmosets, fraternal twins share gentic information with theirsibling, sometimes passing their siblings genetic information along instead of

their own. this would increase relatedness of helpers

Parent Offspring Conflict

- kin selection helps to explain why there is conflict between parents and offspring and among

siblings

- genetic asymmetry: selection will favor mothers than provide less investment than their

offspring desire and selection will favor offspring that demand more attention than their

mothers are willing to give

Reciprocal Altruism- altruism can also evolve if altruistic acts are reciprocated

- 1. must have an opportunity to interact often

- 2. have the ability to keep track of support given and received and

- 3. provide support only to those who help them

- in primates the conditions for the evolution of reciprocal altruism probably are satisfied often,

and there is some evidence that it occurs

- reciprocal grooming

- male relationships based on reciprocity not relatedness

- a few studies suggest that males keep track of these contingencies at least over short periods

Chapter 8: Primate Life Histories and the Evolution of Intelligence

Big Brains and Long Lives

- go together in most mammalians

- defines the primate order

- selection for larger brains generates selection for longer ways

- brain is 2% of our body weight but accounts for 20% of our metabolism

Life History Theory

- life history theory focuses on the evolutionary forces that shape trade offs between the quantity

and quality of offspring and between current and future reproduction

- energy that is diverted from current reproduction to maintenance enables individuals to

survive and reproduce successfully in the future

- aging and death result from trade offs between reproduction at different ages and survivorship

- death might seem like natural wear and tear but its not

- why doesnt natural selection due away with aging?


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- building higher quality organisms consumes time and resources thus reducing

the organisms growth rate and early fertility

- the trade off between survival and reproduction is strongly biased against the characteristics

that prolong life at the expense of early survival or reproduction

- aging is favored by selection because traits that increase fertility at young ages are

favored at the expense of traits that increase longevity- selective pressure is weaker on traits that affect only the old (because the organism has

probably already reproduced so it doesnt greatly affect evolution)

- the trade offs between current and future reproduction and between the quantity and quality of

offspring generate constellations of interrelated traits

- the trade-off between current and future reproduction depends on ecological factors that

influence survival rates

- predation pressure

- competition for resources

- life history strategies that characterize an organism reflect the net effects of ecological

pressures- natural selection shifts the life history traits in response to changes in environmental conditions

- primates fall toward the slow/long end of the life history continuum

Selective Pressures Favoring Large Brains in Monkeys and Apes

- social or ecological pressures may have favored cognitive evolution in monkeys and apes

- social intelligence hypothesis: the hypothesis that the relatively sophisticated cognitive

abilities of higher primates are the outcome of selective pressures that favored

intelligence as a means to gain advantages in social groups

- hypothesis that primates evolved bigger brains because they rely heavily on extracted

foods that require complex processing- hypothesis that development was due to facilitating behavioural flexibility--> ability to

innovate and find new solutions

- comparative analyses provide some support for all of the hypotheses about cognitive evolution

in primates

- difficult to measure cognitive ability in other species, measuring of the neocortex region

- neocortex region is associated with problem solving and behavioural complexity

- reports of behavioural innovation, examples of social learning and observation of tool

use are all linked to large brains and added complexity

- great apes do not fit the social intelligence hypothesis very well

- live in smaller groups

What do other monkeys know about one another?

-knowledge of third party relationships

- monkeys and apes know something about kinship relationships among other members of their

groups


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- vervets, played a scream of a juvenile vervet the mother looked towards the scream the

longest and the other monkeys looked at the mother---> indicating they knew of the kin

relationship

- young female taught to identify the mother child pair and then was able to identify all

pairs that were related as such

- redirected aggression, when a monkey is threatened or attacked it responds bythreatening or attacking the sibling of the offensive monkey

- monkeys probably understand rank relationships among other individuals

-participation in coalitions probably draws on sophisticated cognitive abilities

- even the simplest coalition is complex

- ally has to access the situation and weigh the gains and risks associated with helping

- knowledge of others is useful because it allows primates to predict how others will

behave

- theory of mind: knowledge of others mental states

- it is difficult to be sure what non human primates know about the minds of other individuals.

however, primatologists have begun to make some progress in this area- experiment where a subordinate is given the opportunity to steal food from the

dominant chimp, food item hidden behind a barrier so it could only be seen by the

subordinate and one was in plain view of the dominant. if the subordinates knew what

the dominant could see then it would go for the food behind the barrier. the chimps did

this most of the time

- human social cognition is more sophisticated than that of apes

- human child and ape performed the same in tasks of physical cognition but children

were considerably more successful at tasks that involved social cognition

The value of studying primate behaviour- if we gain insight on how evolution shaped the behaviour of animals so like us we may have

greater insights about the way evolution shaped our own behaviour

- learn something about our ancestors

Chapter 9: From Tree Shrew to Ape

bipedal: walking upright

-primarily looking at the cenezoic era


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era period epoch period begins(mya)

notableevents

cenezoic quartenary recent

pleistocene

0.012

1.8

origins of

agriculture and

complex societies

appearance of

homo sapiens

tertiary pliocene

miocene

oligocene

eocene

paleocene

5

23

34

54

65

dominance of land

by angiosperms,

mammals, birds

and insects

Continental Drift and Climate Change

- to understand the evolution of our species it is important to understand the geological, climatic

and biological conditions under which these evolutionary changes occurred

- the positions of the continents have changed relative to each other and to the poles

- continental drift: movement of the continents

- pangaea: the massive single continent that contained all of the Earths dry land until

about 120mya

- laurasia: the more northerly of the two supercontinents- gondwanaland: the more southerly of two supercontinents that existed from about

100mya to roughly 120mya. Gondwanaland included Africa, South America, Antarctica

and Australia

- continental drift is important for 2 reasons

- oceans serve as barriers that separate certain species from one another

- one of the engines of climate change and climate change has fundamentally influenced

human evolution

- the climate has changed substantially during the last 65 million years--first becoming warmer

and less variable, then cooling and finally fluctuating widely in temperature

- large continents tend to have severe weather- when continents restrict the circulation of water from the tropics to the poles world

climates seem to become cooler

The Methods of Paleontology

- much of our knowledge of the history of life comes from the study of fossils, the mineralized

bones of dead organisms


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- there are several radiometric methods for estimating the age of fossils

- radiometric methods: any method that takes advantage of the fact that isotopes change

at constant rates

- potassium-argon dating: used to date the age of volcanic rocks, use the ratio of

potassium and argon, argon gas is boiled out at the extremely high temperatures so any

argon present must be due to the decay of potassium.- carbon 14 dating: living animals and plants incorporate this isotope, the ratio is

constant when the animal is alive but when it dies carbon-14 starts to decay to N-14 at a

constant rate

- thermoluminescence dating: based on an effect of high energy nuclear particles

traveling through rock. where the particles pass through they dislodge electrons and

these get trapped somewhere else in the crystal lattice, heat relaxes the bonds and light

is given off as electrons move back

- electron-spin-resonance dating: used to determine the age of apatite crystals, an

inorganic component of tooth enamel

- uranium-lead dating: ratio of uranium to lead to date zirconium crystals found inigneous rocks

- different technique for different periods, potassium dating for the distant past carbon-14

only 40,000yrs

- absolute radiometric dating is supplemented by relative dating methods based on magnetic

reversals and comparison with other fossil assemblages

- radiometric problems:

-particular site may not contain samples appropriate for radiometric dating

- relatively large margins of error

- magnetic field reversals have the same pattern for a given time period, certain

rocks record the direction of the magnetic field

The Evolution of the Early Primates

- the evolution of flowering plants created a new set of ecological niches. Primates were among

the animals that evolved to fill these niches.

- during the 1st two thirds of the mezozoic, forests where dominated by gymnosperms

(trees)

- with the break up of Pangaea in the Cretaceous period came angiosperms (flowering

plants)

- arboreal animals that could find, manipulate and chew these fruits could exploit new

niches

- the ancestors of modern primates were small bodied nocturnal quadrupeds much like

contemporary shrews

-plesiadapiforms: any member of a group of primate like mammals that lived during the

Paleocene. although many paleontologists do not consider them primates the

plesiadapiforms were probably similar to the earliest primates who lived around the

same time

- claws and no opposable big toe


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- C. simpsoni had an opposable big toe

- the discovery of C. simpsoni helps explain why natural selection favored the basic features of

primate morphology

- grasping hands and feet, leaping locomotion

- enhanced the ability of early primates to exploit a new array of plant resources

- grasping hands and feet preceded eyes in the front evidence works with C. simpsoni-primates with modern features appeared in the Eocene epoch

- omomydae and adapidae

- omomydae were probably nocturnal adapidae probably diurnal they were generally

larger and their postcranial bones suggest they were active like modern lemurs

The First Happlorrhines

- during the oligocene epoch, many parts of the world became colder and drier

-by the end of the eocene the continents were more or less like they are today

- cold currents reduced the transfer of heat

-primates similar to modern monkeys may have first evolved during the Eocene, but theyradiated during the Oligocene

- the Fayum

- three groups of happlorhine primates

-parapithecids

- diverse group with the dental formation that has been retained in new

world monkeys

- oligopithecids

- the oldest in the Fayum, orbits fully enclosed in bone, dental formula of

old world, share some features with strepsirrhines

-propliopithecids- dental formula of the old world monkeys

-primates appear in south america for the first time during the oligocene but it is unclear where

they came from or how they got there

- earliest found in Bolivia, teeth suggest that they were frugivores

- some think they got there by rafting but that seems highly unlikely, most intriguing

hypothesis suggests that the happlorhines appeared in Africa much earlier when a trans-

atlantic journey was more plausible

The emergence of the hominoids

- the early miocene was warm and moist but by the end of the epoch the world had become much

cooler and more arid

- east african rift appeared changing the tropical forest of east africa to be replaced by

woodlands and savannas

- contemporary apes differ from monkeys in posture and forms of locomotion and this is

reflected in their skeletal anatomy

- monkeys leap and stay on top of branches while apes hang below branches, they have

little need for a tail so they can have more of a stiff back and sit upright


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- the first evidence of adaptations for suspensory locomotion comes from Miocene fossils

collected nearly 40 years ago but overlooked until recently

- morotopithecus bishopi

- other early Miocene apes were similar to Morotopithecus in their dentition but more like

monkeys in their postcranial anatomy

-proconsulids: early miocene hominids-proconsul had a large grasping thumb, something we see in humans but not modern

apes or monkeys

- the middle miocene epoch saw a new radiation of hominoids and the expansion of hominoids

throughout much of Eurasia

- differed from proconsuls

- zygomatic arches were flared outward to make room for larger jaw muscles

- features were a response to the climatic shift from a moist tropical environment to a

drier more seasonal environment with tougher vegetation and harder seeds

- climatic changes in the late middle Miocene reduced hominoid diversity in asia and europe

- apes of the late Miocene are not well known particularly in Africa. Recent finds fill in some ofthe gaps

- last common ancestor of gorrillas, humans and chimps lived about 8-9 mya, last

common to chimps and humans around 5-7mya

- there are no clear candidates for the ancestors of humans or any modern apes except perhaps

orangutans

- evolutionary history of apes is still poorly understood

- during the early and middle Miocene, ape species were plentiful and monkey species were not.

In the late Miocene and early Pliocene, many ape species became extinct and were replaced by

monkeys

- evolution is not synonymous with progress

Documents

Human Evolution Textbook notes for Midterm (Chapters 1-9)