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Principles of

Evolution

• Has become a unifying principle in Biology

• For >150 years, stimulated controversy – mostly nonscientists

• Initial theory sparked controversy within science and biology

The History of Evolutionary Thought

Early History

• Preceded Darwin • Ancient philosophers explained nature

in terms of– What they imagined to be true– Not based on observation

• In 1500s, European philosophers began to exhibit discontent

1. 427–347 B.C.—Plato

2. 384–322 B.C.—Aristotle - ScalaNaturae

The History of Evolutionary Thought3. Until 1700's—Creationism

• James Ussher (17th century, “Biblical”) Sunday, October 23, 4004 BC

a. Each species was created individually by God

b. Earth was the center of the universe

c. Man stood atop creation

The History of Evolutionary Thought

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4. 1707–1788—G.L. Buffon—creation provided a relatively small number of founding species that evolved through natural processes

5. 1769–1832—G. Cuvier—theory of catastrophism

The History of Evolutionary Thought The History of Evolutionary Thought

6. 1807–1873—L. Agassiz—new creation after each catastrophe: proposed at least 50 separate catastrophes and creations

7. 1726–1797—J. Hutton—developed uniformitarianism

8. 1797–1875—C. Lyell—supported Hutton

9. 1744–1829—Lamarck—inheritance of acquired characteristics

The History of Evolutionary Thought

Where Idea Came From?

• Darwin’s Voyage on “Beagle” shaped many ideas of Biology

• Purpose of voyage– Sail around world &

survey little known coastal areas

Darwin’s Finches

• Galapagos formed from volcanoes

• Finch ancestors came from South America

– Different islands, different environments

– Today – each island has own species

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(a) large ground finch, beak suited to large seeds

(b) small ground finch, beaksuited to small seeds

(c) warbler finch, beaksuited to insects

(d) tree finch, beak suited to leaves

10.1809–1882—C. Darwin—developed the theory of evolution; species evolved through natural selection and an adaptation to their ever-changing environment

11.1823–1913—A. Wallace—supported Darwin's theory

The History of Evolutionary Thought Darwin’s Observations

• Populations have inherent potential to increase exponentially

Darwin’s Observations

• Populations are fairly constant in size over long periods of times

Darwin’s Observations

• Natural resources are limited

• Competition important in limiting survival

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Darwin’s Observations

• There is variation within individuals of a population & variations are inherited

Darwin’s Deductions

• Only some organisms survive

• There is a struggle for existence among individuals in population

Darwin’s Deductions

• Individuals with favorable variations are more likely to survive and reproduce

Darwin’s Deductions

• Accumulation of variation over many generations is evolution

• When great enough – a new species

• A gradual process

What Exactly are Species?

• Distinct if they do not interbreed in nature

• All have differences within them

– Traits in population change– Eventually new species arise

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Evidence of Evolution

Fossils 1. Transitional forms are evidence of

evolutionary change

2. Controversies over the interpretation of fossil data a. Dating of fossils b. Do fossils really show transitional forms?

Stages of Fossilization

(a) (b) (c)

Teeth became larger andharder, reflecting a changein diet from soft leaves andbuds to more abrasivegrasses.

Selection for fastrunning on the openplains favored the evolution of stout,strong legs and large,hard hooves.

If a modern horse hadsmall teeth like these,the teeth would beground away while it was still very young.

Body size increased,perhaps in responseto selection by predators.

Merychippus

Hyracotherium

forefoottooth

Paleotheres

Archaeohippus Anchitherium

Pliohippus

Mesohippus

Hipparion

Equus

brow

sing

graz

ing

Evidence of evolution• Comparative

anatomy

Homologous structures

Evidence of evolution• Comparative

anatomy

All mammals evolved from common ancestor

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Evidence of evolutionComparative anatomy

Analogous structures have similar form & function, but are structurally quite different

Evidence of evolution

Convergent evolution

Unrelated organisms evolve similar adaptive characteristics

Evidence of evolutionComparative anatomy:

Vestigial structures

These vestigial bones are similar in structure to those of the salamander but serve no function. All three animals inherited the bones from a common ancestor.

salamander

whale

snake

Evidence of EvolutionComparative embryology

All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches

Fish Snake Chicken Mouse Human

Evidence of Evolution

Comparative biochemistry and molecular biology

All cells have DNA, RNA, ribosomes, the same 20 amino acids, and use ATP as an energy carrier

Evidence of Evolution

Comparative biochemistry and molecular biology

DNA similarities

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Evidence of Evolution

• Artificial selection

Is Evolution Happening Today?

Recent examples

1. Antibiotic resistance in bacteria

2. Pesticide resistance in insects

Patterns in Evolution?• Different from original Darwin model

– Gradualism – Darwin described evolution as a slow & gradual process

– Evolution may occur more rapid than earlier thought

• “Punctuated equilibrium”

– Evolution does not always occur

Patterns in Evolution? Present-day EvolutionKey concepts

1. The variations upon which natural selection works are produced by chance mutations

2. Selection produces organisms that are well adapted to a particularenvironment

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Present-day Evolution

3. The processes of evolution select for organisms that are best adapted to a particular environment—"survival of the fittest"

4. These processes occur constantly in all the species of life on Earth