15.1 Darwin15.1 Darwin’’s Theory of Natural Selections Theory of Natural Selection

Main idea: Main idea: Charles Darwin developed a theory of Charles Darwin developed a theory of evolution based on natural selectionevolution based on natural selection

ObjectivesObjectives Discuss the evidence that convinced Darwin Discuss the evidence that convinced Darwin

that species could change over time.that species could change over time. List the four principles of natural selection.List the four principles of natural selection. Show how natural selection could change a Show how natural selection could change a

populationpopulation

New VocabularyNew Vocabulary Selective breeding, Artificial selection, Natural Selective breeding, Artificial selection, Natural

selection, Evolutionselection, Evolution

Charles DarwinCharles Darwin boarded boarded the HMS Beaglethe HMS Beagle in in 18311831..Most believed the world Most believed the world was about was about 6,0006,000 years old. years old.During the shipDuring the ship’’s five year s five year voyage, Darwin made voyage, Darwin made extensive collections of extensive collections of rocks, rocks, fossilsfossils, plants and , plants and animals.animals.

He also read Charles LyellHe also read Charles Lyell’’s s Principles of Principles of Geology Geology – a book proposing the Earth – a book proposing the Earth was was millionsmillions of years old. of years old.

Developing the Theory of Developing the Theory of Natural SelectionNatural Selection

In 1835, the Beagle arrived in the In 1835, the Beagle arrived in the Galapagos Islands off the coast of South Galapagos Islands off the coast of South America.America.Darwin began to collect mockingbirds, Darwin began to collect mockingbirds, finches, and other animals on the finches, and other animals on the fourfour islands. islands. He noticed that the He noticed that the differentdifferent islandsislands seemed to have their own, slightly seemed to have their own, slightly differentdifferent varieties varieties of animals.of animals.

Developing the Theory of Developing the Theory of Natural SelectionNatural Selection

HMS BeagleHMS Beagle

Almost every Almost every specimen specimen that Darwin that Darwin had collected had collected on the islands on the islands was new to was new to European European scientists. scientists.

Darwin suspected populations from the mainland Darwin suspected populations from the mainland changedchanged after reaching the Galápagos. after reaching the Galápagos.

Galápagos IslandsGalápagos Islands

Developing the Theory of Developing the Theory of Natural SelectionNatural Selection

Darwin hypothesized that Darwin hypothesized that newnew species species could appear could appear graduallygradually through small through small changeschanges in ancestral species. in ancestral species.

Darwin inferred that if humans could Darwin inferred that if humans could change species by change species by artificial selectionartificial selection (selective breeding), then perhaps the (selective breeding), then perhaps the same process could work in same process could work in naturenature..

Developing the Theory of Developing the Theory of Natural SelectionNatural Selection

Darwin called his theory Darwin called his theory Natural SelectionNatural Selection

Developing the Theory of Developing the Theory of Natural SelectionNatural Selection

Natural SelectionNatural Selection

He reasoned that, He reasoned that, given enough time, given enough time, natural selection could natural selection could modifymodify a population a population enough to produce a enough to produce a new species.new species.

Basic Principles of Natural SelectionBasic Principles of Natural Selection

Darwin published Darwin published On the Origin of SpeciesOn the Origin of Species by Means of Natural Selection by Means of Natural Selection in 1859.in 1859.

Today, biologists use the term evolution to Today, biologists use the term evolution to define define changeschanges in groups of organisms in groups of organisms through through time.time.

DarwinDarwin’’s theory of natural selection is s theory of natural selection is NOT NOT the same as evolution. Natural selection is the same as evolution. Natural selection is a means of explaining a means of explaining HOW HOW evolutionevolution works.works.

The Origin of SpeciesThe Origin of Species