Darwinian EvolutionDarwinian Evolution

EvolutionEvolution

►Evolution is the accumulated change Evolution is the accumulated change in the in the frequencies of alleles frequencies of alleles within within isolated gene poolsisolated gene pools due to the due to the selective pressure of the environment selective pressure of the environment such the population becomes unable such the population becomes unable to reproduce with any other and can to reproduce with any other and can be said to be a new be said to be a new speciesspecies..

““On the Origin of Species”On the Origin of Species”

► Title of Charles Title of Charles Darwin’s book Darwin’s book

► Published Published December, 1859December, 1859

► Sold out in one daySold out in one day

““A century and a half A century and a half later, it still argues later, it still argues the case for the case for evolution better than evolution better than any other book. “ any other book. “ Edward J. Larson, Edward J. Larson, EvolutionEvolution

Darwin’s Case for EvolutionDarwin’s Case for Evolution- Artificial Selection- Artificial Selection

► An idea with which An idea with which people were people were comfortablecomfortable

► Farmers select for Farmers select for breeding only the breeding only the animals or plants that animals or plants that have the traits they likehave the traits they like Fast horses, plants with Fast horses, plants with

the biggest fruitthe biggest fruit

►Named this process Named this process “artificial selection” “artificial selection”

Darwin’s Case for EvolutionDarwin’s Case for Evolution

Artificial SelectionArtificial Selection

Artificial Selection Artificial Selection of Wild of Wild Mustard (Mustard (Brassica oleracea)Brassica oleracea)

Darwin’s Case for Evolution –Darwin’s Case for Evolution – VarietyVariety also exists in nature also exists in nature

– among species

Darwin’s Case for EvolutionDarwin’s Case for Evolution- and (more

importantly) varietyvariety also exists within species

- Genetic DiversityGenetic Diversity

Darwin’s Case for EvolutionDarwin’s Case for EvolutionOverproduction of OffspringOverproduction of Offspring

In nature, many more In nature, many more

individuals areindividuals are

born than canborn than can

possibly survive.possibly survive.Thomas MalthusThomas Malthus

Darwin’s Case for EvolutionDarwin’s Case for Evolution

Why can’t they all survive?Why can’t they all survive?

Limiting Factors (Limiting Factors (factors that limit pop. sizefactors that limit pop. size)) PredationPredation Food supply Food supply CompetitionCompetition ShelterShelter MatesMates

Darwin’s Case for EvolutionDarwin’s Case for EvolutionA high rate of reproduction combined A high rate of reproduction combined

with competition for food, shelter, and with competition for food, shelter, and mates creates a struggle for mates creates a struggle for existence. existence.

The fiercest struggle is among individuals The fiercest struggle is among individuals of the same species, for they share of the same species, for they share the same niche, habitat, and dangers.the same niche, habitat, and dangers.

Darwin’s Case for EvolutionDarwin’s Case for Evolution

““Can we doubt that individuals having an Can we doubt that individuals having an advantage, however slight, over advantage, however slight, over others, would have the best chance of others, would have the best chance of surviving and procreating their surviving and procreating their kind?...This preservation of favorable kind?...This preservation of favorable conditions… I callconditions… I call

Natural SelectionNatural Selection.”.”

What was Darwin Proposing?What was Darwin Proposing?

1.1. Competition among species for limited Competition among species for limited resources leads to differential survival resources leads to differential survival and reproduction (natural selection).and reproduction (natural selection).

2.2. Organisms of different kinds Organisms of different kinds descended from a common ancestor.descended from a common ancestor.

3.3. The number of different kinds of The number of different kinds of species multiplied over time.species multiplied over time.

4.4. Evolution occurs through gradual Evolution occurs through gradual changes in a population.changes in a population.

Darwin’s EvidenceDarwin’s Evidence

Fossil RecordFossil Record

► Over millions Over millions of years, of years, deposits deposits compress older compress older sediments sediments below into below into layerslayers

More recent

Older

Darwin’s EvidenceDarwin’s EvidenceFossil RecordFossil Record► embryology in embryology in

extinct organisms extinct organisms similar to that in similar to that in living organismsliving organisms

Darwin’s EvidenceDarwin’s EvidenceEmbryologyEmbryology Similarities in patterns of development Similarities in patterns of development

among different species today suggest among different species today suggest common ancestor:common ancestor:

ChickChick

PigPig

HumanHuman

Darwin’s EvidenceDarwin’s EvidenceMorphologyMorphology (the form and structure of an organism) (the form and structure of an organism)

► Homologous structuresHomologous structures Similarities in morphology of different organisms suggest common (Similarities in morphology of different organisms suggest common (samesame) ancestor) ancestor

Darwin’s EvidenceDarwin’s EvidenceVestigial StructuresVestigial Structures

- morphologies which no longer function- morphologies which no longer function

Darwin’s EvidenceDarwin’s Evidence

Morphology Morphology ––

Imperfect StructuresImperfect Structures::

structurestructure

not perfect fornot perfect for

function, but servesfunction, but serves

purposepurpose

Geese have up to 20 vertebrae – very flexible!

Giraffe has only 7 vertebrae – NOT very flexible!

Darwin’s EvidenceDarwin’s EvidenceGeographic proximity of similar speciesGeographic proximity of similar species

– species on different Galapagos Islands – species on different Galapagos Islands were more similar to one another than were more similar to one another than they were to those on mainland they were to those on mainland

Remaining 19Remaining 19thth Century Century QuestionsQuestions

Natural Selection Special Natural Selection Special CreationCreation

The complexity and perfection of structures such as the The complexity and perfection of structures such as the human eye indicates the work of a supernatural human eye indicates the work of a supernatural Designer.Designer.

William PaleyWilliam Paley

Natural selection results in better-adapted organs and Natural selection results in better-adapted organs and organisms, not perfect ones.organisms, not perfect ones.

Charles DarwinCharles Darwin

►Darwin did not attempt to Darwin did not attempt to scientifically answer the question of scientifically answer the question of life’s originlife’s origin

Remaining 19Remaining 19thth Century Century QuestionsQuestions

►What about gaps in the fossil What about gaps in the fossil record?record? What about “great leaps” forward?What about “great leaps” forward?

►Is the Earth old enough for the slow Is the Earth old enough for the slow process of natural selection?process of natural selection?

►How does inheritance work?How does inheritance work?►What causes individuals with new What causes individuals with new

variations to appear?variations to appear?