PowerLecture: Chapter 24 Principles of Evolution

PowerLecture:PowerLecture:Chapter 24Chapter 24

Principles of EvolutionPrinciples of Evolution

Learning ObjectivesLearning Objectives

Understand how variation occurs in Understand how variation occurs in populations and how changes in allele populations and how changes in allele frequencies can be measured.frequencies can be measured.

Know how mutations, gene flow, genetic Know how mutations, gene flow, genetic drift, and natural selection can influence the drift, and natural selection can influence the rate and direction of pop ulation change.rate and direction of pop ulation change.

Describe the types of selection mechanisms Describe the types of selection mechanisms that help shape populations.that help shape populations.

Characterize the mechanisms of isolation Characterize the mechanisms of isolation that promote speciation. that promote speciation.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Be able to cite what biologists generally Be able to cite what biologists generally accept as evidence to support concepts of accept as evidence to support concepts of evolution. Explain how observations from evolution. Explain how observations from comparative morphology and comparative comparative morphology and comparative biochemistry are used to reconstruct the biochemistry are used to reconstruct the past.past.

Describe how life might have spontaneously Describe how life might have spontaneously arisen on Earth approximately 3.5 billion arisen on Earth approximately 3.5 billion years ago. years ago.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Understand the general physical features Understand the general physical features and behavioral patterns attributed to early and behavioral patterns attributed to early primates. Know their relationship to other primates. Know their relationship to other mammals. mammals.

Trace primate evolutionary development. Trace primate evolutionary development. Understand the distinction between Understand the distinction between

hominoid and hominid.hominoid and hominid.

Impacts/IssuesImpacts/Issues

Measuring TimeMeasuring Time

Measuring Time Measuring Time

How do we measure time?How do we measure time? In geologic time we recognize In geologic time we recognize

that asteroids from the that asteroids from the beginning of the universe are beginning of the universe are still orbiting the sun.still orbiting the sun.

About 65 million years ago one About 65 million years ago one of these asteroids hit Earth, of these asteroids hit Earth, causing the extinction of the causing the extinction of the dinosaurs and other forms of dinosaurs and other forms of life.life.

Measuring Time Measuring Time

Humanlike species were evolving in Africa Humanlike species were evolving in Africa about 5 million years ago.about 5 million years ago.

Modern humans have been around for about Modern humans have been around for about 100,000 years.100,000 years.

Change could occur in the future, especially if Change could occur in the future, especially if the large asteroid predicted for 2028 happens the large asteroid predicted for 2028 happens to sweep a bit too close to Earth.to sweep a bit too close to Earth.

Video: Asteroid MenaceVideo: Asteroid Menace

From ABC News, Biology in the Headlines, 2005 DVD.From ABC News, Biology in the Headlines, 2005 DVD.

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How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

A large asteroid impact could obliterate A large asteroid impact could obliterate civilization and much of Earth’s biodiversity. civilization and much of Earth’s biodiversity. Should we spend millions, even billions, of Should we spend millions, even billions, of dollars to search for and track asteroids?dollars to search for and track asteroids? a. Yes, even though the chance of impact is low, a. Yes, even though the chance of impact is low,

stakes are high. With warning, we can minimize stakes are high. With warning, we can minimize damage. damage.

b. No, the likelihood of an impact is very low and b. No, the likelihood of an impact is very low and the cost is high, so it is not worth it. the cost is high, so it is not worth it.

Section 1Section 1

A Little Evolutionary HistoryA Little Evolutionary History

A Little Evolutionary History A Little Evolutionary History

EvolutionEvolution is defined by biologists as is defined by biologists as genetic change in a line of descent through genetic change in a line of descent through successive generations.successive generations.

In the 1800s, the source of Earth’s amazing In the 1800s, the source of Earth’s amazing diversity of life forms was a matter of dispute.diversity of life forms was a matter of dispute.

The prevailing belief in creation was being The prevailing belief in creation was being challenged by evidence supplied from new challenged by evidence supplied from new investigatory tools in the fields of geology and investigatory tools in the fields of geology and comparative anatomy.comparative anatomy.


In 1831, botanist John Henslow arranged In 1831, botanist John Henslow arranged for a 22-year-old Charles Darwin to take for a 22-year-old Charles Darwin to take ship as a naturalist aboard the HMS ship as a naturalist aboard the HMS BeagleBeagle..

Throughout the trip, Darwin studied and Throughout the trip, Darwin studied and collected a variety of plants and animals.collected a variety of plants and animals.

Darwin returned after Darwin returned after five years at sea and five years at sea and with other scientists with other scientists began pondering the began pondering the growing evidence that growing evidence that life forms change over time.life forms change over time.

Figure 24.1Figure 24.1

Fig 24.1a(1), p 444

GalápagosIslands

EQUATOR

route ofBeagle

Animation: The Galapagos IslandAnimation: The Galapagos Island

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Animation: Finches of the GalapagosAnimation: Finches of the Galapagos

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Thomas Malthus had suggested that as a Thomas Malthus had suggested that as a population outgrows its resources, its population outgrows its resources, its members must compete for what is members must compete for what is available; some will not make it.available; some will not make it.

Darwin’s observations found support for this Darwin’s observations found support for this idea in nature; chance could be part of the idea in nature; chance could be part of the equation, but so was the variation of traits equation, but so was the variation of traits among members of the same species.among members of the same species.

Darwin’s work eventually led to the proposal of Darwin’s work eventually led to the proposal of natural selectionnatural selection; decades later, genetics ; decades later, genetics would provide understanding of how those traits would provide understanding of how those traits could vary in the first place.could vary in the first place.

Section 2Section 2

A Key Evolutionary Idea: A Key Evolutionary Idea: Individuals VaryIndividuals Vary

A Key Evolutionary Idea: Individuals Vary A Key Evolutionary Idea: Individuals Vary

Evolution has two major components:Evolution has two major components: MicroevolutionMicroevolution refers to the cumulative refers to the cumulative

genetic changes that give rise to new species.genetic changes that give rise to new species.

MacroevolutionMacroevolution applies to the large-scale applies to the large-scale patterns, trends, and rates of change among patterns, trends, and rates of change among groups of species.groups of species.


Individuals don’t evolve—populations do.Individuals don’t evolve—populations do. Evolution occurs only where there is change in Evolution occurs only where there is change in

the genetic makeup of a population.the genetic makeup of a population.• A A populationpopulation is a group of individuals belonging to is a group of individuals belonging to

the same species, occupying the same given area.the same species, occupying the same given area.• Members of a population demonstrate certain Members of a population demonstrate certain

morphological, physiological, and behavioral traits in morphological, physiological, and behavioral traits in common. common.

• Populations exhibit Populations exhibit

immense variation immense variation

among their among their

individual members.individual members. Figure 24.2Figure 24.2


Variation comes from genetic differences.Variation comes from genetic differences. All of the genes of a population make up the All of the genes of a population make up the

gene poolgene pool, but the genes have slightly different , but the genes have slightly different forms called alleles.forms called alleles.

Variations in traits in a population result when Variations in traits in a population result when individuals inherit different combinations of individuals inherit different combinations of alleles.alleles.


Section 3Section 3

Microevolution: Microevolution:

How New Species AriseHow New Species Arise

Microevolution: Microevolution: How New Species Arise How New Species Arise

Mutation produces new forms of genes.Mutation produces new forms of genes. Mutations are heritable changes in DNA and Mutations are heritable changes in DNA and

are the only source of new gene forms.are the only source of new gene forms.• Mutations are rare events.Mutations are rare events.• Whether they are harmful (lethal mutation), neutral, Whether they are harmful (lethal mutation), neutral,

or beneficial depends on how the altered gene or beneficial depends on how the altered gene product performs under prevailing conditions.product performs under prevailing conditions.

The majority of mutations are probably harmful, The majority of mutations are probably harmful, altering traits in such a way that an individual altering traits in such a way that an individual cannot survive or reproduce. cannot survive or reproduce.


Natural selection can reshape the genetic Natural selection can reshape the genetic makeup of a population.makeup of a population.

The The theory of evolution by natural selectiontheory of evolution by natural selection proposed by Darwin has several major points:proposed by Darwin has several major points:

• Individuals of a population vary in form, functioning, Individuals of a population vary in form, functioning, and behavior.and behavior.

• Many variations can be passed from generation to Many variations can be passed from generation to generation.generation.

• Some forms of a trait are more advantageous than Some forms of a trait are more advantageous than others; they improve chances of surviving and others; they improve chances of surviving and reproducing.reproducing.


• Natural selection is the difference in survival and Natural selection is the difference in survival and reproduction that occurs among individuals differing reproduction that occurs among individuals differing in one or more traits.in one or more traits.

• A population is evolving when some forms of a trait A population is evolving when some forms of a trait are increasing/decreasing, indicating changes in the are increasing/decreasing, indicating changes in the commonality of the alleles.commonality of the alleles.

• Over time, shifts in the makeup of the gene pools Over time, shifts in the makeup of the gene pools have generated Earth’s diverse life forms.have generated Earth’s diverse life forms.

AdaptationAdaptation describes the tendency for describes the tendency for organisms to come to have the characteristics organisms to come to have the characteristics that suit them best to the conditions of their that suit them best to the conditions of their environment.environment.


Chance can also change a gene pool.Chance can also change a gene pool. Genetic driftGenetic drift is the random fluctuation in allele is the random fluctuation in allele

frequencies over time due to chance frequencies over time due to chance occurrences alone.occurrences alone.

• It is more rapid in small populations.It is more rapid in small populations.• In the In the founder effectfounder effect, a few individuals (carrying , a few individuals (carrying

genes that may/may not be typical of the whole genes that may/may not be typical of the whole population) leave the original population to establish population) leave the original population to establish a new one.a new one.

Animation: Simulation of Genetic DriftAnimation: Simulation of Genetic Drift

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In In gene flowgene flow, genes move with the individuals , genes move with the individuals when they move out of, or into, a population.when they move out of, or into, a population.

• The physical flow of alleles tends to minimize genetic The physical flow of alleles tends to minimize genetic variation between populations.variation between populations.

• It decreases the effects of mutation, genetic drift, and It decreases the effects of mutation, genetic drift, and natural selection.natural selection.

The ability to interbreed defines a species.The ability to interbreed defines a species. A A speciesspecies is one or more populations of is one or more populations of

individuals who can interbreed under natural individuals who can interbreed under natural conditions and produce fertile offspring.conditions and produce fertile offspring.


Populations of one species are reproductively Populations of one species are reproductively isolated from other populations.isolated from other populations.

• Reproductive isolationReproductive isolation is the stoppage of gene flow is the stoppage of gene flow between two populations.between two populations.

• In geographic isolation, barriers restrict gene flow In geographic isolation, barriers restrict gene flow between populations.between populations.

• Reproductive isolating mechanisms include isolation Reproductive isolating mechanisms include isolation of gametes, structural isolation, isolation in time, of gametes, structural isolation, isolation in time, unworkable hybrids, and behavioral isolation.unworkable hybrids, and behavioral isolation.

Animation: Reproductive Animation: Reproductive Isolating MechanismsIsolating Mechanisms

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DivergenceDivergence is the process whereby local units is the process whereby local units of a population become reproductively isolated of a population become reproductively isolated from other units and thus experience changes from other units and thus experience changes in gene frequencies between them, which may in gene frequencies between them, which may be enough to halt interbreeding and lead to be enough to halt interbreeding and lead to speciationspeciation. .


time A time B time C time D

daughter species

parent species

time

Fig 24.4a, p.447

daughter species


Speciation can occur gradually or in Speciation can occur gradually or in “bursts.”“bursts.”

According to the According to the gradualismgradualism model, new model, new species emerge through many small changes in species emerge through many small changes in form over long spans of time.form over long spans of time.

In the In the punctuated equilibriumpunctuated equilibrium model, most model, most evolutionary changes occur in bursts.evolutionary changes occur in bursts.

Animation: Models of SpeciationAnimation: Models of Speciation

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Animation: Directional SelectionAnimation: Directional Selection

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Section 4Section 4

Looking at Fossils Looking at Fossils

and Biogeographyand Biogeography

Looking at Fossils and Biogeography Looking at Fossils and Biogeography

A A fossilfossil is recognizable physical evidence is recognizable physical evidence of ancient life.of ancient life.

Fossils are found in sedimentary rock.Fossils are found in sedimentary rock. The most common fossils are bones, teeth, The most common fossils are bones, teeth,

shells, seeds, and the other hard parts of shells, seeds, and the other hard parts of different organisms.different organisms.

Figures 24.5 and 24.6Figures 24.5 and 24.6


Fossilization begins with burial in sediments or Fossilization begins with burial in sediments or volcanic ash.volcanic ash.

• Water invades, depositing ions and inorganic Water invades, depositing ions and inorganic compounds.compounds.

• Pressure from accumulating sediments transforms Pressure from accumulating sediments transforms the trapped material into stony fossils.the trapped material into stony fossils.

• Organisms are most likely to be preserved when Organisms are most likely to be preserved when they are buried rapidly and in the absence of oxygen.they are buried rapidly and in the absence of oxygen.

StratificationStratification is the layering of sedimentary is the layering of sedimentary deposits formed over long geologic time.deposits formed over long geologic time.


Completeness of the fossil record varies.Completeness of the fossil record varies. The fossil record is incomplete: large-scale The fossil record is incomplete: large-scale

movements in the Earth’s crust have obliterated movements in the Earth’s crust have obliterated evidence from crucial periods, and soft-bodied evidence from crucial periods, and soft-bodied organisms decayed rather than fossilized.organisms decayed rather than fossilized.

• Population densities and body size further skew the Population densities and body size further skew the record.record.

• The fossil record is also heavily biased toward The fossil record is also heavily biased toward certain environments.certain environments.

Radiometric datingRadiometric dating tracks the radioactive tracks the radioactive decay of isotopes trapped in sediments to allow decay of isotopes trapped in sediments to allow scientists to date the fossils they do find.scientists to date the fossils they do find.

Animation: Radioisotope DecayAnimation: Radioisotope Decay

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Animation: Radiometric DatingAnimation: Radiometric Dating

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Biogeography provides other clues. Biogeography provides other clues. BiogeographyBiogeography addresses the question of why addresses the question of why

certain species occur where they do on the certain species occur where they do on the surface of the earth.surface of the earth.

• The simplest explanation is that they evolved there The simplest explanation is that they evolved there from ancestral species.from ancestral species.

• Alternatively, they may have dispersed there from Alternatively, they may have dispersed there from someplace else.someplace else.

The study of The study of plate tectonicsplate tectonics reveals that the reveals that the continents once formed a giant supercontinent continents once formed a giant supercontinent called called PangeaPangea, thus shedding light on the , thus shedding light on the possible dispersal routes for different species.possible dispersal routes for different species.

© 2007 Thomson Higher Education

PACIFICPLATE

COCOSPLATE

NAZCAPLATE

NORTHAMERICAN

PLATE

SOUTHAMERICAN

PLATE

EURASIAN PLATE

AFRICAN PLATE

SOMALI PLATE

PACIFIC PLATE

PHILLIPINEPLATE

INDO-AUSTRALIAN

PLATE

ANTARCTIC PLATE

Fig 24.7a, p.449

Animation: Plate TectonicsAnimation: Plate Tectonics

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Fig 24.7b, p.449

65 mya420 mya 260 mya 10 mya

Animation: Geological Time ScaleAnimation: Geological Time Scale

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Section 5Section 5

Comparing the Form and Comparing the Form and Development of Body PartsDevelopment of Body Parts


Comparing body forms may reveal Comparing body forms may reveal evolutionary connections.evolutionary connections.

Through Through comparative morphologycomparative morphology, , researchers reconstruct evolutionary history on researchers reconstruct evolutionary history on the basis of information contained in the the basis of information contained in the observed patterns of body form.observed patterns of body form.

• Homologous structuresHomologous structures are the same body are the same body features that have become modified in different lines features that have become modified in different lines of descent from common ancestors (morphological of descent from common ancestors (morphological divergence).divergence).

• One example of this would be the bones in the One example of this would be the bones in the forelimbs of vertebrates.forelimbs of vertebrates.

1

1

1

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a. early reptile

b. pterosaur

c. chicken

d. bat

e. porpoise

f. penguin

g. human

Fig 24.8, p.450


Analogous structuresAnalogous structures are used for similar are used for similar functions in similar environments by dissimilar functions in similar environments by dissimilar and distantly related species.and distantly related species.

Morphological convergenceMorphological convergence is the adoption of is the adoption of similar form and function over periods of time similar form and function over periods of time (example: the distinctive torsos of dolphins and (example: the distinctive torsos of dolphins and tuna).tuna).

Animation: Morphological DivergenceAnimation: Morphological Divergence

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Development patterns also provide clues. Development patterns also provide clues. Different organisms may show similarities Different organisms may show similarities

in morphology during their embryonic stages; in morphology during their embryonic stages;

these similarities often indicate evolutionary these similarities often indicate evolutionary

relationships.relationships.• Some of the variation seen in adult vertebrates is Some of the variation seen in adult vertebrates is

due to mutations in regulatory genes that control the due to mutations in regulatory genes that control the rates of growth of different body parts.rates of growth of different body parts.

• One example can be seen in chimpanzees and One example can be seen in chimpanzees and humans; as infants skull structure is virtually humans; as infants skull structure is virtually identical, but adults have very different appearances.identical, but adults have very different appearances.

fish reptile bird (chicken) mammal (human)

Fig 24.9a, p 451

fish reptile bird (chicken) mammal (human)

Fig 24.9a, p 451

Stepped Art

adult shark

human embryo (three millimeters long)

Fig 24.9b, p 451© 2007 Thomson Higher Education

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infant adult

adult

a. Chimpanzee skull

Fig 24.10, p 451

b. Human skull

infant

Animation: Morphing SkullsAnimation: Morphing Skulls

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Vestigial structuresVestigial structures are apparently useless are apparently useless structures that are left over from a time when structures that are left over from a time when more functional versions were important for an more functional versions were important for an ancestor.ancestor.

backbone(vertebralcolumn)

pelvic girdle (hind legs

attach to these)

coccyx (boneswhere manyother mammalshave a tail)

small boneattached topelvic girdle

thighboneattached topelvic girdle

Fig. 24.11, p.451

Animation: Comparative Pelvic AnatomyAnimation: Comparative Pelvic Anatomy

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Section 6Section 6

Comparing BiochemistryComparing Biochemistry

Comparing Biochemistry Comparing Biochemistry

Genes and gene products Genes and gene products (proteins) of different species (proteins) of different species contain information about contain information about evolutionary relationships. evolutionary relationships.

By comparing body form, for By comparing body form, for example, all primates appear to example, all primates appear to be related; this can be be related; this can be confirmed or denied based on confirmed or denied based on analysis of the amino acid analysis of the amino acid sequences in proteins.sequences in proteins.

Figure 24.15a-bFigure 24.15a-b


The degree of similarity of amino acid The degree of similarity of amino acid sequences is a measure of species sequences is a measure of species relatedness; fewer differences indicate a closer relatedness; fewer differences indicate a closer relationship and vice versa.relationship and vice versa.

Cytochrome Cytochrome cc is an example of a protein that is an example of a protein that has changed very little over time; in humans has changed very little over time; in humans and chimps, the sequence is identical, but there and chimps, the sequence is identical, but there are 19 amino acid differences between humans are 19 amino acid differences between humans and turtles.and turtles.


Nucleotide sequences can also be analyzed Nucleotide sequences can also be analyzed for neutral mutations, which provide for neutral mutations, which provide information on variation over time; information on variation over time; calculations of neutral mutations can give calculations of neutral mutations can give an indication of “when” species divergence an indication of “when” species divergence occurred—a occurred—a molecular clockmolecular clock..

Section 7Section 7

How Species How Species Come and GoCome and Go

How Species Come and Go How Species Come and Go

ExtinctionExtinction is the irrevocable loss of a is the irrevocable loss of a species.species.

Background extinctionBackground extinction is the steady rate of is the steady rate of species disappearance over time as local species disappearance over time as local conditions change.conditions change.

Mass extinctionMass extinction is the disappearance of major is the disappearance of major groups of species on a global scale due to groups of species on a global scale due to catastrophic events.catastrophic events.

Human activities have led to an increase in the Human activities have led to an increase in the extinction rate in the past few centuries.extinction rate in the past few centuries.

How Species Come and Go How Species Come and Go

In adaptive radiation, new species arise.In adaptive radiation, new species arise. In In adaptive radiationadaptive radiation, new species move into , new species move into

new habitats during bursts of microevolution.new habitats during bursts of microevolution.• Many adaptive radiations have occurred in the first Many adaptive radiations have occurred in the first

few million years following major mass extinction few million years following major mass extinction events.events.

• Mammals, for example, arose and radiated into the Mammals, for example, arose and radiated into the habitats vacated by extinction of the dinosaurs.habitats vacated by extinction of the dinosaurs.

Adaptive radiations have also occurred in Adaptive radiations have also occurred in humans; humans; Homo erectusHomo erectus radiated away from radiated away from Homo habilisHomo habilis some 2 million years ago and some 2 million years ago and eventually gave rise to eventually gave rise to Homo sapiensHomo sapiens about about 100,000 years ago.100,000 years ago.

Fig 24.12., p.452

1.8 meters (6 feet)

thighbone(femur)

shinbone(tibia)

Neandertal Modern Inuit Homo erectus Modern Masai

Animation: Genetic Distance Animation: Genetic Distance Between Human GroupsBetween Human Groups

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Fig 24.13, p.453

New Guinea, Australia

Pacific Islands

Southeast Asia

Arctic, Northeast Asia

North, South America

Northeast Asia

Europe, Middle East

Africa

genetic distance0% =0.1%0.2%

Proposed Family Tree for Proposed Family Tree for Homo SapiensHomo Sapiens

Artificial SelectionArtificial Selection

Figures 24.25 and 24.26Figures 24.25 and 24.26

Section 8Section 8

Endangered SpeciesEndangered Species

Endangered Species Endangered Species

Human activities are Human activities are

driving many species driving many species

to extinction.to extinction. An An endangered endangered

speciesspecies is an is an

endemic species that endemic species that

is very vulnerable to extinction; is very vulnerable to extinction; endemicendemic species are those found only in one region species are those found only in one region of the world and nowhere else.of the world and nowhere else.


Endangered Species Endangered Species

Habitat loss is the major threat to more than Habitat loss is the major threat to more than 90% of the endangered species.90% of the endangered species.

Introduction of exotic species is also displacing Introduction of exotic species is also displacing endemic species.endemic species.

Human trade in animals and animal parts also Human trade in animals and animal parts also claims a large toll.claims a large toll.


Section 9Section 9

Evolution from a Evolution from a Human PerspectiveHuman Perspective

Evolution from a Human Perspective Evolution from a Human Perspective

All forms of life can be classified and All forms of life can be classified and grouped for greater ease in understanding grouped for greater ease in understanding their evolutionary relationships.their evolutionary relationships.

The binomial system of nomenclature used two The binomial system of nomenclature used two names—genus and species—to identify each names—genus and species—to identify each distinct organism.distinct organism.

Modern systems use several groupings to Modern systems use several groupings to organize the genera (from the broadest organize the genera (from the broadest grouping down to the most specific grouping): grouping down to the most specific grouping): domain, kingdom, phylum, class, order, family, domain, kingdom, phylum, class, order, family, genus, and species.genus, and species.

Classification of HumansClassification of Humans


Five trends mark human evolution.Five trends mark human evolution. Precision grip and power grip.Precision grip and power grip.

• PrehensilePrehensile movements allowed fingers to wrap movements allowed fingers to wrap around objects in a grasp.around objects in a grasp.

• Opposable thumb and fingers allowed more refined Opposable thumb and fingers allowed more refined use of the hand.use of the hand.

• The The precision gripprecision grip and and power grippower grip movements of movements of the human hand allowed for tool making.the human hand allowed for tool making.


Improved daytime vision: resulted from forward Improved daytime vision: resulted from forward directed eyes (depth perception) with their directed eyes (depth perception) with their increased ability to discern shape, movement, increased ability to discern shape, movement, color, and light intensity.color, and light intensity.

Changes in dentition: resulted in humans Changes in dentition: resulted in humans having smaller teeth of more having smaller teeth of more

uniform length; generally the uniform length; generally the

jaws and teeth became less jaws and teeth became less

specialized.specialized. Jaw shape and teeth of an early primate


Changes in the brain and behavior.Changes in the brain and behavior.• The brain increased in size and complexity, resulting The brain increased in size and complexity, resulting

in new behaviors.in new behaviors.• CultureCulture evolved; culture is composed of all the evolved; culture is composed of all the

behavior patterns that are passed between behavior patterns that are passed between generations by learning and symbolic behavior, generations by learning and symbolic behavior, especially language.especially language.

Fig 24.16, p.455

post-reproductiveyears

adult

subadult

infancy

18 24 30 34 38

time in uterus (weeks)

lem

ur

mac

aq

ue

gib

bo

n

ch

imp

hu

ma

n

10

20

30

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60

70


Upright walking.Upright walking.• BipedalismBipedalism is the is the

habitual two-legged habitual two-legged gait characteristic of gait characteristic of humans.humans.

• Compared with Compared with monkeys and apes, monkeys and apes, humans have a humans have a shorter, S-shaped, shorter, S-shaped, somewhat flexible somewhat flexible backbone, which backbone, which works with shoulder works with shoulder blades and pelvic blades and pelvic girdle to allow for girdle to allow for upright movement.upright movement.


Fig 24.17b, p 455

foramenmagnum

Fig 24.17c, p 455

foramenmagnum

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Section 10Section 10

Emergence of Emergence of Early HumansEarly Humans

Emergence of Early Humans Emergence of Early Humans

Apelike forms, the Apelike forms, the hominoidshominoids, spread , spread through Africa, Asia, and Europe between through Africa, Asia, and Europe between 23 and 5 million years ago.23 and 5 million years ago.

At this time, the earth began to change and At this time, the earth began to change and most of the hominoids most of the hominoids

went extinct.went extinct. One survivor was the One survivor was the

common ancestor of common ancestor of

both the great apes and both the great apes and

the first the first hominidshominids.. Figure 24.18b-cFigure 24.18b-c


Early hominids lived in Central Africa.Early hominids lived in Central Africa. Sahelanthropus tchadensisSahelanthropus tchadensis was one of the was one of the

first species to evolve in Central Africa about 6 first species to evolve in Central Africa about 6 to 7 million years ago, during the time when the to 7 million years ago, during the time when the

ancestors of humans were becoming distinct ancestors of humans were becoming distinct from the apes.from the apes.

Australopithecus afarensisAustralopithecus afarensis is one of the is one of the species that walked upright across the African species that walked upright across the African plain some 3.7 million years ago.plain some 3.7 million years ago.

Animation: Fossils of AustralopithsAnimation: Fossils of Australopiths

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Is Is Homo sapiensHomo sapiens “out of Africa”? “out of Africa”? Species of Species of humanshumans appeared a little over 2 appeared a little over 2

million years ago in eastern Africa; the earliest million years ago in eastern Africa; the earliest humans were humans were Homo habilisHomo habilis and and Homo Homo rudolfensisrudolfensis..

• They had increased brain size, a smaller face, and They had increased brain size, a smaller face, and thickly enameled teeth, which permitted a wider thickly enameled teeth, which permitted a wider variety of diet.variety of diet.

• They also used tools.They also used tools.

Fig 24.18d, p 456

H. habilis1.9–1.6 million years

Fig 24.18e, p 456

Homo rudolfensis2.4–1.8 million years


Divergence produced Divergence produced Homo erectusHomo erectus; these ; these early humans began migrating out of Africa into early humans began migrating out of Africa into Europe and Asia in waves. Europe and Asia in waves.

• Homo erectusHomo erectus still lived in Southeast still lived in Southeast Asia Asia between 53,000 and 37,000 years ago.between 53,000 and 37,000 years ago.

• NeanderthalsNeanderthals lived as recently as 30,000 years ago lived as recently as 30,000 years ago in Europe and the Near East, and their extinction in Europe and the Near East, and their extinction

coincided with the origin of modern humans between coincided with the origin of modern humans between 40,000 and 30,000 years ago.40,000 and 30,000 years ago.


Where did Where did Homo sapiensHomo sapiens originate? originate? Two models are used to interpret the evidence Two models are used to interpret the evidence

provided by measurements of small genetic provided by measurements of small genetic differences seen among humans today:differences seen among humans today:

• The The multiregional modelmultiregional model proposes that proposes that Homo Homo sapienssapiens evolved from evolved from Homo erectusHomo erectus in the various in the various parts of the world to which it migrated many years parts of the world to which it migrated many years before; gene flow prevented speciation.before; gene flow prevented speciation.

• In the In the African emergence modelAfrican emergence model, , Homo sapiensHomo sapiens originated in Africa and migrated out to replace the originated in Africa and migrated out to replace the Homo erectusHomo erectus populations already there; various populations already there; various lines of evidence support this model.lines of evidence support this model.

Fig 24.20b, p 457

H. sapiensfossil from Ethiopia,

160,000 years old

Fig 24.20a, p.457

40,000 years ago

60,000 years ago

160,000 years ago

35,000-60,000 years ago

15,000-30,000 years ago

Animation: Primate Evolutionary TreeAnimation: Primate Evolutionary Tree

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Section 11Section 11

Earth’s History and Earth’s History and the Origin of Lifethe Origin of Life

Earth’s History and the Origin of Life Earth’s History and the Origin of Life

Primordial Earth was a hard place 4 billion Primordial Earth was a hard place 4 billion years ago, but within 200 million years life years ago, but within 200 million years life had appeared on its surface.had appeared on its surface.



Conditions on early Earth were intense.Conditions on early Earth were intense. The early atmosphere was likely composed of The early atmosphere was likely composed of

gaseous hydrogen, nitrogen, carbon monoxide, gaseous hydrogen, nitrogen, carbon monoxide, and carbon dioxide; there likely was no oxygen and carbon dioxide; there likely was no oxygen or water.or water.

Cooling and solidification of the Earth’s crust Cooling and solidification of the Earth’s crust allowed water to condense and rain to fall, allowed water to condense and rain to fall, creating early seas.creating early seas.

Organic materials and water were necessary for Organic materials and water were necessary for the beginnings of life.the beginnings of life.


Biological molecules paved the way for cells Biological molecules paved the way for cells to evolve.to evolve.

The first living cells probably emerged around The first living cells probably emerged around 3.8 billion years ago and resembled modern 3.8 billion years ago and resembled modern anaerobic bacteria.anaerobic bacteria.

Prior to this first cell, however, Prior to this first cell, however, chemical chemical evolutionevolution would have had to occur. would have had to occur.

Figure 24.22aFigure 24.22a

spontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions

livingcells

self-replicating system enclosed in aselectively permeable, protective lipid sphere

DNA RNA enzymes andother proteins

formation ofprotein-RNA systems,

evolution of DNA

formation oflipid spheres

membrane-bound proto-cells

Fig 24.23a, p.459

spontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions

livingcells

self-replicating system enclosed in aselectively permeable, protective lipid sphere

DNA RNA enzymes andother proteins

formation oflipid spheres

formation ofprotein-RNA systems,

evolution of DNA

membrane-bound proto-cells

Fig 24.23a, p.459

Stepped Art


Experiments give us ideas about how life Experiments give us ideas about how life first arose on Earth.first arose on Earth.

Simulations of the conditions on early Earth Simulations of the conditions on early Earth show how molecules such as amino acids, show how molecules such as amino acids, glucose, ribose, deoxyribose, and other sugars glucose, ribose, deoxyribose, and other sugars could have been produced.could have been produced.

How did complex compounds such as proteins How did complex compounds such as proteins form?form?

• One scenario of chemical synthesis proposes that One scenario of chemical synthesis proposes that clay templates served as “enzymes” to favor bond clay templates served as “enzymes” to favor bond formation among chemicals.formation among chemicals.

• Alternatively, complex compounds may have first Alternatively, complex compounds may have first formed near deep-sea hydrothermal vents.formed near deep-sea hydrothermal vents.


Enzymes, ATP, and other molecules could have Enzymes, ATP, and other molecules could have assembled spontaneously in places where they assembled spontaneously in places where they were in close physical proximity, which would were in close physical proximity, which would have promoted chemical interactions—the have promoted chemical interactions—the beginnings of metabolic pathways.beginnings of metabolic pathways.

From accumulated organic compounds emerged From accumulated organic compounds emerged replicating systems consisting of DNA, RNA, replicating systems consisting of DNA, RNA, proteins, and enzymes.proteins, and enzymes.

Perhaps RNA strands were capable of enzyme activity Perhaps RNA strands were capable of enzyme activity (as has recently been demonstrated) and promoted (as has recently been demonstrated) and promoted protein synthesis.protein synthesis.

The first cells were probably membrane-bound sacs The first cells were probably membrane-bound sacs containing nucleic acids that served as templates for containing nucleic acids that served as templates for proteins.proteins.

Animation: Miller’s Reaction Animation: Miller’s Reaction Chamber ExperimentChamber Experiment

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Animation: Milestones in Animation: Milestones in the History of Lifethe History of Life

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PowerLecture: Chapter 24 Principles of Evolution