Darwin and Evolution Chapter 17. Darwin and Evolution 2Outline History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend

Darwin and Evolution

Chapter 17

Darwin and Darwin and EvolutionEvolution 2

OutlineOutlineHistory of Evolutionary ThoughtHistory of Evolutionary Thought

Darwin’s Theory of EvolutionDarwin’s Theory of Evolution Earth very oldEarth very old

Descend with change from a common ancestor Descend with change from a common ancestor

Adaptation to a changing environmentAdaptation to a changing environment

The Evidence of EvolutionThe Evidence of Evolution FossilFossil

BiogeographicalBiogeographical

AnatomicalAnatomical

BiochemicalBiochemical

3

Voyage of the HMS Beagle


History of Evolutionary ThoughtHistory of Evolutionary Thought

Prior to DarwinPrior to DarwinView of nature determined by deep-seated View of nature determined by deep-seated beliefsbeliefs

Held to be intractable truthsHeld to be intractable truths

Biology thought had slowly begun to acceptBiology thought had slowly begun to accept

Various ideas of evolutionVarious ideas of evolution

Similarities between living things reflect recent Similarities between living things reflect recent common ancestrycommon ancestry

Dissimilarities between living things reflect Dissimilarities between living things reflect ancient common ancestryancient common ancestry


Mid-Eighteenth CenturyMid-Eighteenth CenturyTaxonomy matured during mid-eighteenth Taxonomy matured during mid-eighteenth

centurycenturyLinnaeusLinnaeus believed in: believed in: The fixity of speciesThe fixity of species

That each species had:That each species had: An ideal structure and function, andAn ideal structure and function, and A place in the A place in the scala naturaescala naturae (scale of complexity) (scale of complexity)

Count BuffonCount Buffon:: Wrote 44-volume catalog of all known plants Wrote 44-volume catalog of all known plants and animalsand animals

Suggested descent with modificationSuggested descent with modification


Late Eighteenth CenturyLate Eighteenth Century

CuvierCuvier::First to use comparative anatomy to develop a First to use comparative anatomy to develop a system of classificationsystem of classification

Founded PaleontologyFounded Paleontology

Proposed CatastrophismProposed Catastrophism

Local catastrophes in past had caused later Local catastrophes in past had caused later strata to have a new mix of fossilsstrata to have a new mix of fossils

After each catastrophe, the region was After each catastrophe, the region was repopulated by species from surrounding areasrepopulated by species from surrounding areas

9Evolutionary Thought before DarwinLamarck:

First biologist to:Propose evolution Link diversity with environmental adaptation

Concluded more complex organisms are descended from less complex organismsProposed inheritance of acquired characteristics – Lamarckianism

10Formation of Sedimentary Rock

Charles Lyell:Earth is subject to slow but continuous cycles of erosion and upliftProposed uniformitarianism, rates and processes of change are constant


Darwin’s Theory of EvolutionDarwin’s Theory of Evolution

Geological observations consistent with Geological observations consistent with those of Hutton & Lyellthose of Hutton & Lyell

Biogeographical observations:Biogeographical observations:The study of the geographic distribution of life The study of the geographic distribution of life forms on earthforms on earth

Darwin saw similar species in similar Darwin saw similar species in similar habitats;habitats;

Reasoned related species could be modified Reasoned related species could be modified according to the environmentaccording to the environment

13The Patagonian Hare,Dolichotis

patagoniumDid the Patagonian

Hare resemble a rabbit

because the two types of animals were adapted to the same type of

Environment?

Did the Patagonian

hare have the face of a

guinea pig because of common

descent with guinea pigs?

15Galápagos Tortoises, Geochelone

TortoisesDarwin observed tortoise neck length varied from island to island

Proposed that speciation on islands correlated with a difference in vegetation

16Galápagos Finches

FinchesFinchesDarwin observed many different Darwin observed many different species of finches on various islandsspecies of finches on various islands

Speculated they could have Speculated they could have descended from a single pair of descended from a single pair of mainland finchmainland finch


GeologyandFossilsGeologyandFossils• Darwin began to accept the idea Darwin began to accept the idea

that the earth is very old. And that that the earth is very old. And that there would be enough time for there would be enough time for “descent with modification”“descent with modification” to to occur.occur.

• Darwin decided adaptations Darwin decided adaptations develop over time; he sought a develop over time; he sought a mechanism by which adaptations mechanism by which adaptations might arise.might arise.


Natural Selection & AdaptationNatural Selection & Adaptation

•Natural selectionNatural selectionwas proposed by was proposed by both both Alfred Russel WallaceAlfred Russel Wallace and and DarwinDarwin as a driving mechanism of evolution as a driving mechanism of evolution caused by environmental selection of caused by environmental selection of organisms most fit to reproduce, organisms most fit to reproduce, resulting in resulting in adaptationadaptation..

•Because the environment is always Because the environment is always changing, there is no perfectly-adapted changing, there is no perfectly-adapted organismorganism


Natural Selection & AdaptationNatural Selection & Adaptation

1.1. Individuals have heritable variationsIndividuals have heritable variations

2.2. More individuals produced each More individuals produced each generation than environment can supportgeneration than environment can support

3.3. Some individuals have adaptive Some individuals have adaptive characteristicscharacteristics

Enables increased survival and reproductionEnables increased survival and reproduction

4.4. Increasing proportion of succeeding Increasing proportion of succeeding generations will have these characteristicsgenerations will have these characteristics

5.5. Populations become adapted to their local Populations become adapted to their local environment through change in individualsenvironment through change in individuals


NaturalSelectionNaturalSelectionPreconditions for Natural SelectionPreconditions for Natural Selection

1.1. ThemembersofapopulationhaverandombutThemembersofapopulationhaverandombutheritableheritablevariationsvariations..

2.2. Inapopulation,Inapopulation,moreindividualsareproducedmoreindividualsareproducedthanthanwillsurvive.willsurvive.

3.3. SomeindividualshaveSomeindividualshaveadaptivecharacteristicsadaptivecharacteristicsthatthatenablethemtosurviveandreproducebetter.enablethemtosurviveandreproducebetter.((FitnessFitness))

Consequences of Natural SelectionConsequences of Natural Selection4. Anincreasingproportionofindividualsinsucceeding

generationshavetheadaptivecharacteristics.(Adaptation)

5. Theresultofnaturalselectionisapopulationadaptedtoitslocalenvironment.

21Variation in a Population


Organisms Have VariationsOrganisms Have VariationsDarwin emphasized that individuals from a Darwin emphasized that individuals from a

population vary in their:population vary in their:

Functional characteristics Functional characteristics

Physical characteristics Physical characteristics

Behavioral characteristics Behavioral characteristics

Proposed that these VARIATIONS:Proposed that these VARIATIONS:

Are essentialAre essential

Allow Allow adaptationadaptation to the environment over time to the environment over time

23Artificial Selection of Animals


Organisms Struggle to ExistOrganisms Struggle to Exist

MalthusMalthusEach generation has the same reproductive Each generation has the same reproductive potential as the previous generationpotential as the previous generation

Reproductive potential is greater than Reproductive potential is greater than environment can supportenvironment can support

Death, disease, and famine were Death, disease, and famine were inevitable if population were to have inevitable if population were to have stabilitystability

Individuals experience a constant struggle Individuals experience a constant struggle for survivalfor survival


Organisms Differ in FitnessOrganisms Differ in Fitness

FitnessFitness is the relative reproductive success of is the relative reproductive success of an individualan individual

The most-fit individuals in a population The most-fit individuals in a population capture a disproportionate share of goodiescapture a disproportionate share of goodies

Interactions with the environment determine Interactions with the environment determine which individuals reproduce the mostwhich individuals reproduce the most

AdaptationAdaptation

Changes that help a species become more Changes that help a species become more suited to its environmentsuited to its environment

Product of natural selectionProduct of natural selection


Evidence for EvolutionEvidence for Evolution

Common DescentCommon Descent ““Descent with Modification”Descent with Modification” The hypothesis of The hypothesis of common descentcommon descent is is

supported by many lines of evidence.supported by many lines of evidence.

The more varied the evidence, the more The more varied the evidence, the more certain it becomes.certain it becomes.

Darwin synthesized much of the current Darwin synthesized much of the current data but biochemical research was yet data but biochemical research was yet to come.to come.



1.1.FossilsEvidenceFossilsEvidence

2.2.BiogeographicalEvidenceBiogeographicalEvidence

3.3.AnatomicalEvidenceAnatomicalEvidence

a)a) EmbryologicaldevelopmentEmbryologicaldevelopment

4.4.BiochemicalEvidenceBiochemicalEvidence

Darwin and Darwin and EvolutionEvolution 30The Evidence of Evolution:The Evidence of Evolution:

FossilFossil

Fossil EvidenceFossil EvidenceFossils record the history of life Fossils record the history of life from the pastfrom the past

Document a succession of life forms Document a succession of life forms from the simple to the more from the simple to the more complexcomplex

Sometimes the fossil record is Sometimes the fossil record is complete enough to show descent complete enough to show descent from an ancestorfrom an ancestor



Fossils EvidenceFossils Evidence The The fossil recordfossil record is the history of life recorded by is the history of life recorded by

remains from the past.remains from the past.

Fossils are at least 10,000 years old and include Fossils are at least 10,000 years old and include skeletons, shells, seeds, insects trapped in amber, skeletons, shells, seeds, insects trapped in amber, and imprints of leaves.and imprints of leaves.

The fossil record traces history of life and allows The fossil record traces history of life and allows us to study history of particular organisms.us to study history of particular organisms.

Fossil evidence supports the Fossil evidence supports the common descentcommon descent hypothesis; fossils can be linked over time hypothesis; fossils can be linked over time because they reveal a similarity in form, despite because they reveal a similarity in form, despite observed changes.observed changes.




Fossils EvidenceFossils EvidenceTransitional forms reveal links between groups.Transitional forms reveal links between groups.

Caudipteryx Caudipteryx is between dinosaurs and birds is between dinosaurs and birds

This Chinese fossil shows some dinosaurs had This Chinese fossil shows some dinosaurs had feathers on arms, tail and probably body.feathers on arms, tail and probably body.

Advantages during running and escape gave rise Advantages during running and escape gave rise to birds once lift-off occurred.to birds once lift-off occurred.

Eustheopteron Eustheopteron is an amphibious-like fishis an amphibious-like fish

Seymouria Seymouria is a reptile-like amphibianis a reptile-like amphibian

Therapsids were mammal-like reptilesTherapsids were mammal-like reptiles



Intermediate & Transitional LinksIntermediate & Transitional Links

Charles Darwin acknowledged that the Charles Darwin acknowledged that the fossil record was a serious problem for fossil record was a serious problem for his theory:his theory:

““By the theory of natural selection, all living By the theory of natural selection, all living species have been connected with the species have been connected with the parent-species of each genus, by differences parent-species of each genus, by differences not greater that we see between the natural not greater that we see between the natural and domestic varieties of the same species and domestic varieties of the same species at the present day… the number of at the present day… the number of intermediate and transitional links, between intermediate and transitional links, between all the living and extinct species, must have all the living and extinct species, must have been been inconceivably great.” inconceivably great.”



Fossils EvidenceFossils Evidence According to DarwinAccording to Darwin’’s theory of s theory of

evolution, all animals are descended evolution, all animals are descended from a common ancestor in the from a common ancestor in the distant past. Supposedly, a single distant past. Supposedly, a single primitive species gradually diverged primitive species gradually diverged into two species, then those diverged into two species, then those diverged over millions of generations to the over millions of generations to the point where we now see the major point where we now see the major differences in body plansdifferences in body plans



Fossils EvidenceFossils Evidence When we look at the fossil record When we look at the fossil record

we see that most of these major we see that most of these major differences were present at the differences were present at the earliest appearance of animal earliest appearance of animal life. Darwin himself knew this, life. Darwin himself knew this, and in and in The Origin of SpeciesThe Origin of Species he he called it a called it a ““seriousserious”” problem for problem for his theory. his theory.



Fossils EvidenceFossils Evidence Paleontologists James Valentine and Paleontologists James Valentine and

Douglas Erwin wrote in 1987 that the Douglas Erwin wrote in 1987 that the Cambrian explosion Cambrian explosion ““is real; it is too is real; it is too big to be masked by flaws in the fossil big to be masked by flaws in the fossil record.record.”” And in 1991, Valentine and And in 1991, Valentine and his colleagues wrote that the his colleagues wrote that the Cambrian explosion Cambrian explosion ““was even more was even more abrupt and extensive than previously abrupt and extensive than previously envisioned.envisioned.””



BiogeographicalBiogeographicalDistributions of plants and Distributions of plants and animals across earthanimals across earthConsistent with origin in one Consistent with origin in one locale and then spread to locale and then spread to accessible regionsaccessible regions


All of the marsupials in Australia presumably evolved from a common ancestor


Evidence for EvolutionEvidence for EvolutionBiogeographicalEvidenceBiogeographicalEvidence

Physical factors, such as the location of Physical factors, such as the location of continents, determine where a population continents, determine where a population can spread.can spread. Marsupials arose when South America, Marsupials arose when South America,

Antarctica, and Australia were joined; Antarctica, and Australia were joined; Australia separated before placental Australia separated before placental mammals arose, so only marsupials mammals arose, so only marsupials diversified in Australia.diversified in Australia.

The distribution of organism on the earth is The distribution of organism on the earth is explainable by explainable by ASSUMINGASSUMING that related forms that related forms evolved in one locale. They then diversified evolved in one locale. They then diversified as they spread out.as they spread out.









Vertebrate forelimbs:Vertebrate forelimbs:HomologousHomologous - All contain the - All contain the same sets of bones in similar same sets of bones in similar waysways

Yet they are modified extensively Yet they are modified extensively to meet various adaptive needsto meet various adaptive needs

Darwin interpreted this as Darwin interpreted this as support for a hypothesis of support for a hypothesis of common descentcommon descent

49Significance of Homologous Structures



Homologous Structures:Homologous Structures: Anatomically similar because they are inherited from Anatomically similar because they are inherited from

a common ancestora common ancestor May be functionally similar or notMay be functionally similar or not

Analogous Structures:Analogous Structures: Serve the same functionServe the same function Not constructed similarlyNot constructed similarly Do not share a common ancestorDo not share a common ancestor

Vestigal Structures:Vestigal Structures: Fully-developed anatomical structuresFully-developed anatomical structures Reduced or obsolete functionReduced or obsolete function

51Vestigial Limbs in Whales


Arguments against HomologyArguments against Homology1. If homology is defined as similarity due to 1. If homology is defined as similarity due to

common descent, then it is circular common descent, then it is circular reasoning to use it as reasoning to use it as evidenceevidence for common for common descent.descent.

HomologyCommon Descent


Arguments against HomologyArguments against Homology2. Biologist have known for decades that 2. Biologist have known for decades that

homologous features are homologous features are NOTNOT due to due to similar genes, so the mechanism that similar genes, so the mechanism that produces them remains unknown.produces them remains unknown.

““Because homology implies community of descent Because homology implies community of descent from… a common ancestor it might be thought from… a common ancestor it might be thought that genetics would provide the key to the that genetics would provide the key to the problem of homology. This is were the worst problem of homology. This is were the worst shock of all is encountered…[because] shock of all is encountered…[because] characters controlled by identical genes are not characters controlled by identical genes are not necessarily homologous… [and] homologous necessarily homologous… [and] homologous structures need not be controlled by identical structures need not be controlled by identical genes” genes”

Gavin de BeersGavin de Beers


ArgumentsagainstHomologyArgumentsagainstHomology

Homologous Structures can arise Homologous Structures can arise from different genesfrom different genes

In fruit flies In fruit flies

““even-skipped”even-skipped” gene – development of gene – development of body segments. Not found in all body segments. Not found in all other insectsother insects

““Sex-lethal” gene – sex Sex-lethal” gene – sex determination in fruit flies but not determination in fruit flies but not other insectsother insects


Arguments against HomologyArguments against Homology

Non-homologous structures can arise from Non-homologous structures can arise from identical genes.identical genes.

““Distal-less”Distal-less” gene – an appendage gene – an appendage developmental gene found in:developmental gene found in:

Mice, spiny worms, Butterfly, sea urchins, Mice, spiny worms, Butterfly, sea urchins, velvet wormvelvet worm

Yet the appendages are not homologous Yet the appendages are not homologous either by similar structure or by common either by similar structure or by common ancestry (descent)ancestry (descent)



Embryological developmentEmbryological developmentAll vertebrate embryos have:All vertebrate embryos have:A postanal tail and A postanal tail and Paired pharyngeal (gill) Paired pharyngeal (gill) pouchespouches

57Significance of Developmental Similarities

Embryologicaldevelopment

Allvertebrateembryoshave:

Apostanaltail&

Pairedpharyngeal(gill)pouches

Darwin and Darwin and EvolutionEvolution 59Haeckel’sEmbryosHaeckel’sEmbryos – similarities in early embryos – similarities in early embryos

not only demonstrate that they are descended from not only demonstrate that they are descended from a common ancestor, but also reveal what that a common ancestor, but also reveal what that ancestor looked like.ancestor looked like.

““The [human] embryo itself The [human] embryo itself at a very early period can at a very early period can hardly be distinguished hardly be distinguished from that of other from that of other members of the members of the vertebrate kingdom.” vertebrate kingdom.” Since humans and other Since humans and other vertebrates “pass through vertebrates “pass through the same early stages of the same early stages of development, … we ought development, … we ought frankly to admit their frankly to admit their community of descent” community of descent”

CharlesDarwin,CharlesDarwin,The The Descent of ManDescent of Man


ContraryEvidenceContraryEvidence

Concerning Haeckel’s EmbryosConcerning Haeckel’s Embryos1)1) Include ONLY those classes and Include ONLY those classes and

orders closest to fitting Haeckel’s orders closest to fitting Haeckel’s theory.theory.

2)2) They distort the embryos they purport They distort the embryos they purport to showto show

3)3) (Most Seriously) they entirely omit (Most Seriously) they entirely omit earlier stages in which vertebrate earlier stages in which vertebrate embryos look very different.embryos look very different.


Contrary EvidenceContrary Evidence

Concerning Haeckel’s EmbryosConcerning Haeckel’s Embryos StephenJayGould,StephenJayGould,Natural HistoryNatural HistorymagazinemagazineMarch2000March2000

Gould acknowledged that Haeckel faked his Gould acknowledged that Haeckel faked his drawings. drawings. “To cut to the quick of this drama, “To cut to the quick of this drama, Haeckel had exaggerated the similarities by Haeckel had exaggerated the similarities by idealizations and omissions. He also, in idealizations and omissions. He also, in some cases – in a procedure that can only be some cases – in a procedure that can only be called fraudulent – simply copied the same called fraudulent – simply copied the same figure over and over again.”figure over and over again.”


ContraryEvidenceContraryEvidence

Concerning Haeckel’s EmbryosConcerning Haeckel’s EmbryosStephenJayGould,(StephenJayGould,(Natural HistoryNatural Historymagazine,March2000,pg.45)magazine,March2000,pg.45)

Gould acknowledged that Haeckel faked Gould acknowledged that Haeckel faked his drawings. his drawings. “We do, I think, have the right “We do, I think, have the right to be both astonished and ashamed by the to be both astonished and ashamed by the century of mindless recycling that has led to century of mindless recycling that has led to the persistence of these drawings in a large the persistence of these drawings in a large number, if not a majority, of modern number, if not a majority, of modern textbooks. Atrocious!”textbooks. Atrocious!”


Biochemical EvidenceBiochemical EvidenceAlmost all living organisms:Almost all living organisms:

Use the same basic biochemical moleculesUse the same basic biochemical molecules

Utilize same DNA triplet codeUtilize same DNA triplet code

Utilize same 20 amino acids in their proteinsUtilize same 20 amino acids in their proteins

DNA base-sequence differences:DNA base-sequence differences:

When very similar, suggest recent common When very similar, suggest recent common descentdescent

When more different, suggest more ancient When more different, suggest more ancient common descentcommon descent

65Significance ofBiochemical Differences


ReviewReview

History of Evolutionary ThoughtHistory of Evolutionary Thought

Darwin’s Theory of EvolutionDarwin’s Theory of Evolution Earth very oldEarth very old

Descend with change from a common ancestor Descend with change from a common ancestor

Adaptation to a changing environmentAdaptation to a changing environment

The Evidence of EvolutionThe Evidence of Evolution FossilFossil



BiochemicalBiochemical

Darwin and Evolution

Ending Slide Chapter 17

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Darwin and Evolution Chapter 17. Darwin and Evolution 2Outline History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend