1

I. Evolution and its core principles

• Evolution: cumulative changes in traits of a speciesor population over time.

• Common descent with modification:• The modification of species in successive

generations, with such change sometimes resultingin the formation of new, separate species

• Natural selection:• Differential success in reproduction by different

phenotypes resulting from interactions with theenvironment

• Evolution occurs when natural selection produceschanges in the relative frequencies of alleles in apopulations gene pool.

II. The importance of evolution as aconcept

• As the organizing concept of biology“Nothing in biology makes sense exceptin the light of evolution."Theodosius Dobzhansky

• As an illustration of the scientificmethod.

• As an intellectual revolution

III. Evolutionary thinkingbefore Darwin

• Influences on Darwin

2

• Thales: naturalphenomena bynatural causes

• Plato: “Edos”essentialism

• Single eventcreation

• Essentialism + creationism = Natural theology• Da Vinci and

fossils

Hutton, Lyell, and Geology• Uniformitarianism: Geological forces have, and

still do, mold and shape the Earth

• Gradualism: Geologic change is continuous,slow, and gradual, not catastrophic

• The earth was/is steadily undergoing change.

And, if such a steady change werepossible for the earth, why not for the

creatures that lived on it?

3

Jean-Baptiste de Lamarck: Frenchbiologist, taxonomist, paleobiologist

• Species could changethrough time, changeswere adaptive.

• Occurred throughInheritance ofAcquiredCharacteristics:within life of anindividual, changes inenvironment, internalneeds, cause bodilychanges, whichoffspring inherit.

• Lamarck• believed that changes resulted from an

inherent drive toward perfection.

• identified a line of descent: older fossils tomore recent fossils to modern, livingorganisms

• ideas about the means of evolution wereincorrect, but he figured out that

•Organisms CAN evolve

•One kind of organism can be ancestralto another different kind of organism

4

Georges CuvierFounder ofpaleontology andstratigraphy

Established thatfurther down youwent, the lesssimilar fossilswere to modernforms

Established fact ofextinction

Was a catastrophist

Was adamantlyantievolutionary

Also occurring about thistime:

• Interest in natural history grew

• Worldwide exploration increasedknowledge of diversity

• Systematic investigation of the fossilrecord began

• Geologic information grew

• Leeuwanhoek discoveredmicroorganisms.

IV. Charles Darwin and thetheory of evolution

• Developed the ideas aboutdescent with modification ANDprovided a large body of evidenceto support them

• First person to perceive thatnatural selection is the primaryforce behind evolution

5

About Charles…

• Born 2/12/1809, to wealthy Englishfamily of physicians.

• Dropped out after 2 years medicalschool

• Enrolled in divinity school, aclergyman by 1831

• Spent most of his time collecting andstudying nature

Darwin's journey of discovery

• Dec. 1831 joinedcrew of Britishsurveying ship(HMS Beagle)

• Hired as the crew'snaturalist to makeobservations andcollections

• Darwin was 22years old.

6

Post Beagle:

-Returned to England 5 yrs later.-Now a mature and famous naturalist.-Married, settled down 1842-Suffered from bad health rest of life-Sorted collection, worked on notes andideas-Never taught, participated in scientificsocieties, or ever left England again

The evolution of the theory:A. Perceiving common

descent with modification

During his 5 years at sea andfor a few years after his return,several observations andinfluences led Darwin to hisideas...

• From Lyell :Earth very old, stillchangingGeol. change slow,gradual.

• From fossil record:Extinctions commonRelationship betweenage of fossil and degreeof similarity to modernspecies

• Graded variation innature:Groups of organismscan be classified basedon their similarities

7

Geographical variation-Galapagos Islands

• Endemic species-the finches-the tortoises-iguanas-cacti

• All had mainlandancestors, but onseparate islandshad diverged intoseparate species

Domestication of plants andanimals– artificial selection couldsignificantly alter the traits of aspecies

Thomas Malthus

• wrote Essay on the Principle of Population

• human populations increase geometrically

• food production increases arithmetically

• human population size increases to point:- intense competition for limited resources-poverty, overcrowding, war, famine, disease

• From this Darwin envisions "struggle for existence"as applied to species other than human beings.

8

B. Perceiving natural selection

Development of the naturalselection theory is based onthree inferences that aredrawn from five facts:

• Fact 1: All species have the potential forexponential pop. growth.

• Fact 2: Pop. size generally remains stable.

• Fact 3: Resources are limited.

• Inference 1: Since more individuals areproduced than can be sustained by availableresources, there must be an intense strugglefor existence among individuals of apopulation, resulting in the survival of onlya small portion of each generation.

Fact 4: No two individuals are exactlythe same.Fact 5: Most of this individual variationis heritable.

• Inference 2: Survival isnot random; dependson genetic constitutionof the individual;differential survival isthe process of naturalselection.

• Inference 3: Overmany generations,natural selection willcause a gradual changein populations.

9

Alfred Russel Wallace

• Sent essay to Darwin outlining almostexactly the ideas Darwin had in his owntheory of evolution.

• 1858, both men’s essays presented atmeeting in London.

• Both men formally received equal credit forthe idea of evolution by natural selection.

• 1859, Darwin published On the Origin ofSpecies by Means of Natural Selection, orthe Preservation of Favoured Races in theStruggle for Life.

The theory of evolution isreally a set of related ideas:

• Descent with modification– species change over time

• Natural selection is the mechanism–there are differences in reproduction andsurvival among individuals due togenetically inherited traits.

• Gradualism– species evolve gradually through steadyaccumulation of changes, rather thanabrupt/drastic changes.

Radiometric dating

• Technique used to daterocks

• Compares proportion of aradioactive element to itsnonradioactive decayproduct,

• Time calculated usinguniform rate at which decayoccurs.

• With this technique, fossillayers can be dated todetermine when the plantsand animals in those layerslived.

10

The placement of fossils

• Fossils appear in layers(strata)

• Position of fossils inthe strata reveals theirrelative age

• Fossils are distributedconsistently

• Fossils show linkagesbetween ancestralforms to more recentones via intermediateforms

Biogeography

• Study of species geographicaldistributions (past and present).

• Geographic distribution of organismsreveals relationships

• Example: The Galapagos Islandsspecies

11

Comparative Anatomy : thethe comparison of bodystructures in different species

•Common descent evident inanatomical similaritiesbetween species

Homologous structuresVestigial structures

Homologous structures

Vestigial structures

12

Unrelated species in similarenvironments have evolvedsimilar forms:• Convergent evolution

• Analogous structures

• Homology indicatesancestry,

analogy does not

Comparative Embryology:

• Closely related organisms passthrough very similar stages duringembryonic development.

• Example: all vertebrate embryos passthrough a stage in which they haveopenings called gill pouches on thesides of their throats, which developinto different adult structures

13

Comparative Molecular Biology

• Common set of molecularmachinery for all cells: aminoacids, nucleotides, ATP,genetic code

• Comparisons of amino acid ornucleotide sequences amongspecies, allow construction ofhierarchies of relatedness.

• The greater the similarities,the more closely related twospecies are

• Example: hemoglobin invarious species

Artificial Selection

By choosing which individuals of apopulation will breed and whichwill not, humans have altered thetraits of populations of plants andanimals for thousands of years.This is Artificial not NaturalSelection

Experimental evidence

• In the lab, can alter selectionpressures: (change temperature,predators, food source, etc.)and can alter gene frequencies in apopulation over successivegenerations

• And by mistake--antibiotic resistance