Chapter 22: Descent with Modification: A Darwinian View of Life A Darwinian View of Life Darwin in...

Chapter 22:Chapter 22:

Descent Descent with with

ModificatioModification:n:

A A Darwinian Darwinian

View of LifeView of LifeDarwin in 1840

Overview: Endless Forms Overview: Endless Forms Most BeautifulMost Beautiful

Charles Darwin published Charles Darwin published The Origin of The Origin of Species Species which focused biologists’ which focused biologists’ attention on the great diversity of attention on the great diversity of organismsorganisms

Darwin noted that current species are Darwin noted that current species are descendants of ancestral speciesdescendants of ancestral species

Evolution Evolution can be defined by Darwin’s can be defined by Darwin’s phrase phrase descent with modificationdescent with modification

Evolution can be viewed as both a Evolution can be viewed as both a pattern and a processpattern and a process

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-2Fig. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

1809

1798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.

Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)

Hutton (gradual geologic change)

Lyell (modern geology)

Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

Classification of SpeciesClassification of Species

The Old Testament holds that species The Old Testament holds that species were individually designed by God and were individually designed by God and therefore perfecttherefore perfect

• Carolus Linnaeus interpreted Carolus Linnaeus interpreted organismal adaptations as evidence organismal adaptations as evidence that the Creator had designed each that the Creator had designed each species for a specific purposespecies for a specific purpose

• Linnaeus was the founder of taxonomy, Linnaeus was the founder of taxonomy, the branch of biology concerned with the branch of biology concerned with classifying organismsclassifying organisms


Ideas About Change over Ideas About Change over TimeTime

The study of The study of fossils fossils helped to lay helped to lay the groundwork for Darwin’s ideasthe groundwork for Darwin’s ideas

Fossils are remains or traces of Fossils are remains or traces of organisms from the past, usually organisms from the past, usually found in sedimentary rock, which found in sedimentary rock, which appears in layers or appears in layers or stratastrata

Video: Grand CanyonVideo: Grand Canyon


Fig. 22-3Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

• • PaleontologyPaleontology, the study of, the study of

fossils, was largely developed byfossils, was largely developed by

French scientist Georges CuvierFrench scientist Georges Cuvier

•• CCatastrophismatastrophism, speculating , speculating thatthat

each boundary between strataeach boundary between strata

represents a catastropherepresents a catastrophe


CuviCuvierer

Hutton and LyellHutton and Lyell• • PPerceived that changes in Earth’s erceived that changes in Earth’s surface can result from slow surface can result from slow continuous actions still operating continuous actions still operating todaytoday• • Lyell’s principle of Lyell’s principle of uniformitarianism uniformitarianism states that the states that the mechanisms of change are constant mechanisms of change are constant over timeover time• • This view strongly influenced This view strongly influenced Darwin’s thinkingDarwin’s thinkingLamarckLamarck

• • Hypothesized that species Hypothesized that species evolve through use and disuse evolve through use and disuse of body parts and the of body parts and the inheritance of acquired inheritance of acquired characteristicscharacteristics• • The mechanisms he proposed The mechanisms he proposed are unsupported by evidenceare unsupported by evidence

• • Noted the potential for human Noted the potential for human population to increase faster than population to increase faster than food supplies and other resourcesfood supplies and other resources• • If some heritable traits are If some heritable traits are advantageous, these will advantageous, these will accumulate in the population, and accumulate in the population, and this will increase the frequency of this will increase the frequency of individuals with adaptationsindividuals with adaptations

MalthusMalthus

Darwin’s ResearchDarwin’s Research As a boy and into adulthood, Charles As a boy and into adulthood, Charles

Darwin had a consuming interest in Darwin had a consuming interest in naturenature

Darwin first studied medicine Darwin first studied medicine (unsuccessfully), and then theology at (unsuccessfully), and then theology at Cambridge UniversityCambridge University

After graduating, he took an unpaid After graduating, he took an unpaid position as naturalist and companion to position as naturalist and companion to Captain Robert FitzRoy for a 5-year Captain Robert FitzRoy for a 5-year around the world voyage on the around the world voyage on the BeagleBeagle


The Voyage of the BeagleThe Voyage of the Beagle

Darwin collected specimens of South Darwin collected specimens of South American plants and animalsAmerican plants and animals

Darwin was influenced by Lyell’s Darwin was influenced by Lyell’s Principles Principles of Geology of Geology and thought that the earth was and thought that the earth was more than 6000 years oldmore than 6000 years old

His interest in geographic distribution of His interest in geographic distribution of species was kindled by a stop at the species was kindled by a stop at the Galápagos Islands near the equator west of Galápagos Islands near the equator west of South AmericaSouth America


Video: Galápagos Islands OverviewVideo: Galápagos Islands Overview

Video: Galápagos Sea LionVideo: Galápagos Sea Lion

Darwin’s Focus on AdaptationDarwin’s Focus on Adaptation Darwin perceived Darwin perceived adaptation adaptation to the to the

environment and the origin of new species environment and the origin of new species as closely related processesas closely related processes

Years after Darwin’s voyage, biologists have Years after Darwin’s voyage, biologists have concluded that this is indeed what concluded that this is indeed what happened to the Galápagos fincheshappened to the Galápagos finches

(a) Cactus-eater (b) Insect-eater (c) Seed-eater

In 1844, Darwin wrote an essay on the In 1844, Darwin wrote an essay on the origin of species and origin of species and natural natural selection selection but did not introduce his but did not introduce his theory publicly, anticipating an uproartheory publicly, anticipating an uproar

In June 1858, Darwin received a In June 1858, Darwin received a manuscript from manuscript from Alfred Russell Alfred Russell WallaceWallace, who had developed a theory , who had developed a theory of natural selection similar to Darwin’sof natural selection similar to Darwin’s

Darwin quickly finished Darwin quickly finished The Origin of The Origin of SpeciesSpecies and published it the next year and published it the next year

Darwin and WallaceDarwin and Wallace

The Origin of SpeciesThe Origin of Species

Darwin developed two main ideas:Darwin developed two main ideas:– Descent with modification explains life’s Descent with modification explains life’s

unity and diversityunity and diversity– Natural selection is a cause of adaptive Natural selection is a cause of adaptive

evolutionevolution


Descent with ModificationDescent with Modification

descent with modification = descent with modification = unity of lifeunity of life All organisms are related through All organisms are related through

descent from an ancestor that lived in descent from an ancestor that lived in the remote pastthe remote past

In the Darwinian view, the history of life In the Darwinian view, the history of life is like a tree with branches is like a tree with branches representing life’s diversityrepresenting life’s diversity

Darwin’s theory meshed well with the Darwin’s theory meshed well with the hierarchy of Linnaeushierarchy of Linnaeus


Fig. 22-8Fig. 22-8Hyracoidea(Hyraxes)

Sirenia(Manateesand relatives)

Moeritherium

Barytherium

Deinotherium

Mammut

Elephas maximus(Asia)

Stegodon

Mammuthus

Loxodontaafricana(Africa)

Loxodonta cyclotis(Africa)

010425.52434

Millions of years ago Years ago

Platybelodon

Artificial Selection, Natural Artificial Selection, Natural Selection, and AdaptationSelection, and Adaptation

Darwin noted that humans have Darwin noted that humans have modified other species by selecting modified other species by selecting and breeding individuals with and breeding individuals with desired traits, a process called desired traits, a process called artificial selectionartificial selection

Darwin then described Darwin then described fourfour observationsobservations of nature and from of nature and from these drew these drew two inferencestwo inferences


Observation #1Observation #1: Members of a population : Members of a population often vary greatly in their traitsoften vary greatly in their traits

Observation #2Observation #2: Traits are inherited from : Traits are inherited from parents to offspringparents to offspring


Observation #3Observation #3: All : All species are capable of species are capable of producing more producing more offspring than the offspring than the environment can environment can supportsupport

Observation #4Observation #4: Owing : Owing to lack of food or other to lack of food or other resources, many of resources, many of these offspring do not these offspring do not survivesurvive


Sporecloud

Inference #1Inference #1: Individuals whose : Individuals whose inherited traits give them a inherited traits give them a higher higher probability of surviving and probability of surviving and reproducingreproducing in a given environment in a given environment tend to tend to leave more offspringleave more offspring than than other individualsother individuals

Inference #2Inference #2: This unequal ability of : This unequal ability of individuals to survive and reproduce individuals to survive and reproduce will will lead to the accumulation of lead to the accumulation of favorable traitsfavorable traits in the population over in the population over generationsgenerations


Natural Selection: Natural Selection: A A SummarySummary

Individuals with certain heritable Individuals with certain heritable characteristics survive and reproduce characteristics survive and reproduce at a higher rate than other individualsat a higher rate than other individuals

Natural selection increases the Natural selection increases the adaptation of organisms to their adaptation of organisms to their environment over timeenvironment over time

If an environment changes over time, If an environment changes over time, natural selection may result in natural selection may result in adaptation to these new conditions adaptation to these new conditions and may give rise to new speciesand may give rise to new speciesVideo: Chameleon Video: Chameleon


Fig. 22-12Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

Note that individuals do not evolve; Note that individuals do not evolve; populations evolve over timepopulations evolve over time

Natural selection can only increase Natural selection can only increase or decrease heritable traits in a or decrease heritable traits in a populationpopulation

Adaptations vary with different Adaptations vary with different environmentsenvironments


Direct Observations of Direct Observations of Evolutionary ChangeEvolutionary Change

Two examples provide evidence for Two examples provide evidence for natural selectionnatural selection– the effect of differential predation on the effect of differential predation on

guppy populations guppy populations – the evolution of drug-resistant HIVthe evolution of drug-resistant HIV


Predation and Coloration in Predation and Coloration in Guppies : Guppies : Scientific InquiryScientific Inquiry

Study on the effects of predators on Study on the effects of predators on wild guppy populationswild guppy populations

Brightly colored males are more Brightly colored males are more attractive to femalesattractive to females

Brightly colored males are more Brightly colored males are more vulnerable to predationvulnerable to predation

Pools with fewer predators had more Pools with fewer predators had more brightly colored malesbrightly colored males


Brightly colored guppies (with few Brightly colored guppies (with few predators) where moved to a pool predators) where moved to a pool with many predatorswith many predators

As predicted, over time the population As predicted, over time the population became less brightly coloredbecame less brightly colored

Endler also transferred drab colored Endler also transferred drab colored guppies (with many predators) to a guppies (with many predators) to a pool with few predatorspool with few predators

As predicted, over time the population As predicted, over time the population became more brightly coloredbecame more brightly colored


Natural selection does not create Natural selection does not create new traits, new traits, but edits or selectsbut edits or selects for for traits already present in the traits already present in the populationpopulation

The local environment determines The local environment determines which traits will be selected for or which traits will be selected for or selected against in any specific selected against in any specific populationpopulation


SO……SO……

The Fossil The Fossil RecordRecord The fossil record provides evidence of The fossil record provides evidence of

the extinction of species, the origin of the extinction of species, the origin of new groups, and changes within groups new groups, and changes within groups over timeover time

The Darwinian view of life predicts The Darwinian view of life predicts that evolutionary transitions should that evolutionary transitions should leave signs in the fossil recordleave signs in the fossil record

Paleontologists have discovered Paleontologists have discovered fossils of many such transitional formsfossils of many such transitional forms

Fig. 22-15Fig. 22-15

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

Dep

th (

met

ers

)

0

2

4

6

8

10

12

14

16

18

1

2

3

3

3

1

2

44

Fig. 22-16Fig. 22-16

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

(d) Balaena (recent whale ancestor)

Homologous VS Vestigial Homologous VS Vestigial StructuresStructures

Homology Homology is is similarity resulting similarity resulting from common from common ancestryancestry

Are anatomical Are anatomical resemblances that resemblances that represent variations represent variations on a structural on a structural theme present in a theme present in a common ancestorcommon ancestor


Vestigial Vestigial structures structures are are remnants of features remnants of features that served that served important functions important functions in the organism’s in the organism’s ancestorsancestors

Fig. 22-17Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

Homologies and “Tree Homologies and “Tree Thinking”Thinking”

The Darwinian concept of an The Darwinian concept of an evolutionary tree evolutionary tree of life can explain of life can explain homologieshomologies

Evolutionary trees are hypotheses about Evolutionary trees are hypotheses about the relationships among different groupsthe relationships among different groups

Evolutionary trees can be made using Evolutionary trees can be made using different types of data, for example, different types of data, for example, anatomical and DNA sequence dataanatomical and DNA sequence data


Convergent EvolutionConvergent Evolution Convergent evolution Convergent evolution is the is the

evolution of similar, or evolution of similar, or analogousanalogous,, features in distantly related groupsfeatures in distantly related groups

Analogous traits arise when groups Analogous traits arise when groups independently adapt to similar independently adapt to similar environments in similar waysenvironments in similar ways

Convergent evolution does not Convergent evolution does not provide information about ancestryprovide information about ancestry


BiogeographyBiogeography The geographic distribution of speciesThe geographic distribution of species Islands have many Islands have many endemic endemic (native)(native)

species that are often closely related to species that are often closely related to species on the nearest mainland or islandspecies on the nearest mainland or island

Earth’s continents were formerly united in a Earth’s continents were formerly united in a single large continent called single large continent called PangaeaPangaea, but , but have since separated by have since separated by continental driftcontinental drift

An understanding of continent movement An understanding of continent movement and modern distribution of species allows us and modern distribution of species allows us to predict when and where different groups to predict when and where different groups evolvedevolved


Fig. 22-UN1Fig. 22-UN1

Observations

Over time, favorable traitsaccumulate in the population.

Inferences

and

Individuals in a populationvary in their heritable

characteristics.

Organisms produce moreoffspring than the

environment can support.

Individuals that are well suitedto their environment tend to leave

more offspring than other individuals

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