AP Biology 2006-2007

Chapter 15Darwin and Evolution

Darwin: a reluctant rebel

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Evolution explains the Diversity and Unity of life

1. Diversity – the abundance of different forms of living things on Earth

2. Unity – the biochemical, cellular, genetic,and physiological characteristics/processes common to all living things

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What is Evolution?

The change in a species over time (i.e. the gene pool changes due to adaptations)

1. The Process: Descent thru Modification

new life comes into existence over time all species come from common ancestry all species comes from existing species

via modification

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History of Evolutionary Thought Carolus Linnaeus (1707-

1778) Taxonomist Binomial Nomenclature Agreed with the “fixity of

species” theory However, he performed

hybridization experiments which made him think a species might change with time

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LaMarck Organisms adapted to

their environments by acquiring traits change in their life timechange in their life time

DisuseDisuseorganisms lost parts because they did not use them organisms lost parts because they did not use them — like the missing eyes & digestive system of the — like the missing eyes & digestive system of the tapewormtapeworm

Perfection with Use & NeedPerfection with Use & Needthe constant use of an organ leads that organ to the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith increase in size — like the muscles of a blacksmith or the large ears of a night-flying bator the large ears of a night-flying bat

transmit acquired characteristics to next generation

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History of Evolutionary Thought Alfred Wallace (1823 -1913) British naturalist came up with the same theory as

Darwin independently Natural Selection (Survival of the

Fittest)

Darwin’s and Wallace’s ideas were published at the same time

But Wallace did not have as much evidence as Darwin

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Charles Darwin 1809-1882 British naturalist Proposed the idea of

evolution by natural selection:

Organisms that are best fit for the environment, survive and reproduce (“survival of the fittest”)

Collected clear evidence to support his ideas

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LaMarckian vs. Darwinian view

LaMarck in reaching higher

vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring

Darwin giraffes born with longer

necks survive better & leave more offspring who inherit their long necks

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Robert FitzroyRobert Fitzroy

Voyage of the HMS Beagle Invited to travel around the world

1831-1836 (22 years old!) makes many observations of nature

main mission of the Beagle was to chart South American coastline

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Voyage of the HMS Beagle Stopped in Galapagos Islands

500 miles off coast of Ecuador

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GalapagosRecent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland.

500 miles west of mainland

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Finch? Sparrow?

Woodpecker? Warbler?

Darwin found… birds

Finch? Sparrow?

Woodpecker? Warbler?

Collected many Collected many different birds on the different birds on the Galapagos Islands. Galapagos Islands.

Thought he found Thought he found very different kinds…very different kinds…

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Darwin was amazed to find out: All 14 species of birds were finches…

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Finch? Sparrow?

Woodpecker? Warbler?

Finch? Sparrow?

Woodpecker? Warbler?

But Darwin found… a lot of finches

Large Ground Finch

Small Ground Finch

Warbler Finch Veg. Tree Finch

But there is only one species of finch on the mainland!

How didone species

of finches becomeso many different

species now?

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Tree Thinking

Large-seed eater? Small-seed eater?

Warbler? Leaf-browser?

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Large GroundFinch

Small GroundFinch

Warbler Finch Veg. Tree Finch

Ancestralspecies

Descendantspecies

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Correlation of species to food source

Adaptive radiation

SeedSeedeaterseaters

FlowerFlowereaterseaters

InsectInsecteaterseaters

Rapid speciation:new species filling new niches,

because they inheritedsuccessful adaptations.

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Voyage: 1831-1836

November 24, 1859, Darwin published

“On the Origin of Species by Means of Natural Selection”

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Natural Selection: 4 steps

1. Natural Variation exists in nature

2. Competition - Organisms struggle for survival: more organisms are produced than the environment can support

3. Survival of the fittest: Only the best adapted survives. Adaptations are important

4. Organisms change over time in response to the environment: organisms change but they have a common descent – they have common ancestors

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Adaptations: inherited characteristics that allow individuals to “do better” in their environment. Adaptations increase their chance of survival and reproduction

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Types of Natural Selection

a. Directional – a shift in the freq. of a trait in a particular

direction common in changing

env’ts

Ex. Horseracing: pick horses that can

run fastest

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b. Stabilizing – selects for avg. pheno. and against

extreme pheno. common in stable, unchanging env’t

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c. Disruptive – selects for extreme pheno. and

against avg. pheno. b/c subject to predation

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This is not just a process of the past…

It is all around us today

Artificial selection

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Selective breeding

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Natural Selection vs. Artificial Selection

Artificial Selection: nature provides variation, and humans select variations that we find useful (domestic animals and crops)

Natural Selection: the environment is the selective force. Only those organisms that are well adapted will survive in the wild.

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Sexual Selection