Darwin and Evolution

Chapter 17

2Darwin and EDarwin and Evolutionvolution

OutlineOutlineHistory of Evolutionary ThoughtHistory of Evolutionary ThoughtDarwin’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

3Voyage of the HMS Beagle

4Charles Darwin at 31

5Darwin and EDarwin and Evolutionvolution

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 truthsBiology 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

6Evolutionary Thought before Darwin

7Darwin and EDarwin and Evolutionvolution

Mid-Eighteenth CenturyMid-Eighteenth CenturyTaxonomy matured during mid-eighteenth Taxonomy matured during mid-eighteenth centurycenturyLinnaeus believed in:Linnaeus 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 Buffon:Count 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

8Darwin and EDarwin and Evolutionvolution

Late Eighteenth CenturyLate Eighteenth Century

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

Founded PaleontologyFounded PaleontologyProposed 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

9Darwin and EDarwin and Evolutionvolution

Late Eighteenth CenturyLate Eighteenth CenturyLamarck:Lamarck:

First biologist to:First biologist to:­ Propose evolution Propose evolution ­ Link diversity with environmental adaptationLink diversity with environmental adaptation

Concluded more complex organisms are descended Concluded more complex organisms are descended from less complex organismsfrom less complex organisms

Proposed inheritance of acquired characteristics – Proposed inheritance of acquired characteristics – LamarckianismLamarckianism

Charles Lyell:Charles Lyell: Earth is subject to slow but continuous cycles of Earth is subject to slow but continuous cycles of

erosion and uplifterosion and uplift Proposed uniformitarianism, rates and processes of Proposed uniformitarianism, rates and processes of

change are constantchange are constant

10Formation of Sedimentary Rock

11Darwin and EDarwin and Evolutionvolution

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

12A Glyptodont and a Giant Sloth

13The Patagonian Hare,Dolichotis

patagonium

14Darwin and EDarwin and Evolutionvolution

Galápagos IslandsGalápagos Islands

TortoisesTortoisesDarwin observed tortoise neck length varied Darwin observed tortoise neck length varied from island to islandfrom island to island

Proposed that speciation on islands Proposed that speciation on islands correlated with a difference in vegetationcorrelated with a difference in vegetation

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

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

15Galápagos Tortoises, Geochelone

16Galápagos Finches

17Darwin and EDarwin and Evolutionvolution

Natural Selection and AdaptationNatural Selection and Adaptation

Individuals have heritable variationsIndividuals have heritable variationsMore individuals produced each generation More individuals produced each generation than environment can supportthan environment can support

Some individuals have adaptive Some individuals have adaptive characteristicscharacteristicsEnables increased survival and reproductionEnables increased survival and reproduction Increasing proportion of succeeding Increasing proportion of succeeding generations will have these characteristicsgenerations will have these characteristics

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

18Variation in a Population

19Darwin and EDarwin and Evolutionvolution

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 adaptation to the environment over timeAllow adaptation to the environment over time

20Artificial Selection of Animals

21Artificial Selection of Plants

22Darwin and EDarwin and Evolutionvolution

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 inevitable if Death, disease, and famine were inevitable if population were to have stabilitypopulation were to have stability

Individuals experience a constant struggle for Individuals experience a constant struggle for survivalsurvival

23Darwin and EDarwin and Evolutionvolution

Organisms Differ in FitnessOrganisms Differ in Fitness

Fitness is the relative reproductive success of Fitness is the relative reproductive success of an individualan individualThe 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

AdaptationAdaptationChanges 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

24Transitional Fossils

25Darwin and EDarwin and EvolutionvolutionThe Evidence of Evolution:The Evidence of Evolution:

AnatomicalAnatomicalVertebrate forelimbs:Vertebrate forelimbs:

Homologous - All contain the same sets of Homologous - All contain the same sets of bones in similar waysbones in similar ways

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

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

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

26Biogeography

27Darwin and EDarwin and EvolutionvolutionThe Evidence of Evolution:The Evidence of Evolution:

AnatomicalAnatomicalHomologous 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 notAnalogous 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

28Significance of Homologous Structures

29Significance of Developmental Similarities

30Vestigial Limbs in Whales

31Darwin and EDarwin and EvolutionvolutionThe Evidence of Evolution:The Evidence of Evolution:

Fossil & BiogeographicalFossil & BiogeographicalFossil EvidenceFossil Evidence

Fossils record the history of life from the pastFossils record the history of life from the pastDocument a succession of life forms from the Document a succession of life forms from the simple to the more complexsimple to the more complex

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

BiogeographicalBiogeographicalDistributions of plants and animals across Distributions of plants and animals across earthearth

Consistent with origin in one locale and then Consistent with origin in one locale and then spread to accessible regionsspread to accessible regions

32Darwin and EDarwin and Evolutionvolution

Biochemical EvidenceBiochemical Evidence

Almost all living organisms:Almost all living organisms:Use the same basic biochemical moleculesUse the same basic biochemical moleculesUtilize same DNA triplet codeUtilize same DNA triplet codeUtilize 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

33Significance ofBiochemical Differences

34Darwin and EDarwin and Evolutionvolution

ReviewReviewHistory of Evolutionary ThoughtHistory of Evolutionary ThoughtDarwin’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

Darwin and Evolution

Ending Slide Chapter 17