Charles Darwin (1809-1882) Origin of Species among the most influential texts of this century.

Charles Darwin (1809-1882)

Origin of Species among the most influential texts of this century

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Charles Darwin (1809-1882)• Studied Medicine at Edinburgh

• Switched to become a clergyman at Christ’s College, Cambridge University

• Passionate interest in Natural History

• Reverend (&Professor) John Henslow encouraged him to pursue Biology

• In 1831 invited as a naturalist on the HMS Beagle, a ship sent by British Navy to chart the waters of South America

HMS Beagle off of South America

When Darwin left on the Beagle Evolution was already a popular idea for explaining the fossil record.

However, there were no known mechanismsDarwin did not believe in Evolution, but Rev. Henslow gave him a book to take with him: Lyell’s Principles of Geology

Historical ContextHistorical Context By mid-1800s scientific context was in place for

development of theory of Evolution.

Developments in Geology:

Earth more than 6,000 years oldFossil Record showed change in species over

time

The mechanisms for Evolution were missing, and were hotly debated

Influences on DarwinInfluences on Darwin• GeologyGeology: Darwin had Lyell’s : Darwin had Lyell’s Principles of Principles of

GeologyGeology on board the HMS Beagle on board the HMS Beagle

• Lamarck ’sLamarck ’s (1744-1829) (1744-1829) Theory of EvolutionTheory of Evolution

Inheritance of acquired characteristicsInheritance of acquired characteristics

• Malthus Malthus (1766-1834)(1766-1834): Competition within : Competition within species and struggle for survivalspecies and struggle for survival

• Darwin had Lyell’s book on board the HMS Beagle, given to him by his botany professor, Reverend John Henslow

• Fossil record: • the earth is old• many animals that once existed are now extinct• there are layers (strata) in the fossil record show

a pattern of change

Lyell’s Principles of Geology

Influences on Darwin

Influences on Darwin

http://www.ucmp.berkeley.edu/history/lamarck.html

Jean-Baptiste Lamarck(1744-1829)

Proposed most influential

mechanism of evolution before Darwin

Inheritance of acquired characteristics

Introduced the idea of adaptation, but got the mechanism wrong

Malthus (1766-1834): Essay on the Principles of Population

Influences on Darwin

Competition: not all individuals could surviveRate of population growth >> Rate of increase in food supply

Darwin concluded that individuals that are better adapted would be the ones that survive and leave more offspring

• Darwin held on to his work on natural selection for 20 yrs without publishing

• Alfred Wallace (1823-1913) came up with the idea of natural selection independently

• Darwin rushed to publish Origins in 1859 when he learned of Wallace’s work

• “On the Tendency of Varieties to Depart Indefinitely from the Original Type”

• Based on his work in the Malay Archipelago

Alfred Russel Wallace (1823-1913)

Darwin’s Main PointsDarwin’s Main Points

(1)(1) Organisms EvolveOrganisms Evolve (Darwin not first) (Darwin not first)

(2)(2) Common DescentCommon Descent: species arise from common : species arise from common ancestorsancestors

(3)(3) GradualismGradualism: changes are gradual (still debated): changes are gradual (still debated)

(4)(4) Population SpeciationPopulation Speciation: change in : change in proportionsproportions of individuals having a trait in a populationof individuals having a trait in a population(Darwin’s original idea)(Darwin’s original idea)

(5)(5) Natural SelectionNatural Selection: mechanism (Wallace also): mechanism (Wallace also)

***Lamarck vs Darwin***

• Lamarck: inheritance of acquired traits (not mutations)--Individual evolution

• Evolution at the Population Level

LamarckLamarck

• Individuals are evolving

• If you got a tan, you’d pass it on

LamarckLamarck

• Individuals are evolving

• If you got a tan, you’d pass it on

Balls get tan

LamarckLamarck

• Individuals are evolving

• If you got a tan, you’d pass it on

Tan balls have offspring that are also tan

LamarckLamarck

• Individuals are evolving

• If you got a tan, you’d pass it on

Some get more tan

LamarckLamarck

• Individuals are evolving

• If you got a tan, you’d pass it on

And then pass on their acquired traits

Darwin

• Natural Selection

Darwin

A heritable change(now known as a mutation)

• Natural Selection

Darwin

Selection favors

• Natural Selection

Darwin

GreaterFitness

• Natural Selection

Darwin

GreaterFitness

• Natural Selection

The individuals themselves are not changing, but the population is the unit of evolution

Darwin’s uniqueunique contribution:

Population Speciation as a result of Natural Selection

• More offspring are produced than can survive

• Limited resources and competition for resources

• There is variation in a population

• Individuals better adapted to environment survive

• Survivors leave more offspring (“Survival of the Fittest”)

• Thus, average character of population is altered

"My attention was first thoroughly aroused by comparing together the various specimens ... of the mocking-thrush"

~ C. Darwin, The Voyage of the Beagle (1839)

Darwin’s Mockingbirds (studied Tortoises and finches later)

Galapagos Islands

Darwin’s Mockingbirds

Only one species of mockingbird in South America

But, on each island there was a different species

Mockingbirds on different islands shared traits that suggested a shared common ancestor--and were not independently created

Galapagos Islands

So… Darwin did NOT originate the idea of Evolution…

… BUT he provided a plausible Mechanism

… and much evidence

But, Darwin’s theory was not completeBut, Darwin’s theory was not complete

• Because Darwin knew nothing about mutation, he had no idea how variability was generated in populations (Lecture 5)

• Because Darwin knew nothing about genetics or genes, he had no idea how variability was passed on to offspring (Mendel)

• Darwin did not know about nonadaptive evolutionary forces, such as Genetic Drift (Lecture 3)

• Mendel published in 1865… Mendel published in 1865… was ignored until 1900was ignored until 1900

• Presented a mechanism for Presented a mechanism for how traits got passed onhow traits got passed on

““Individuals pass alleles on to Individuals pass alleles on to their offspring intact”their offspring intact”

(the idea of particulate (genes) inheritance)

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Mendel’s work held Mendel’s work held partpart of the key to what of the key to whatwas missing in Darwin’s Theorywas missing in Darwin’s Theory