Charles Darwin developed the theory of natural selection based on observations from his voyage on the HMS Beagle. He noticed that species on the Galapagos Islands were closely related but had adapted to their environments in slightly different ways. Darwin hypothesized that natural selection - the process by which organisms better adapted to their environment tend to survive and pass on their traits to offspring - could lead to the emergence of new species over many generations. The key principles of natural selection are that traits vary between individuals, traits are heritable, and some traits make individuals more likely to survive and reproduce.

1. 15.1 Darwin15.1 Darwin’s Theory of Natural Selection’s Theory of Natural Selection
Main idea:Main idea: Charles Darwin developed a theory ofCharles Darwin developed a theory of
evolution based on natural selectionevolution based on natural selection
ObjectivesObjectives

Discuss the evidence that convinced DarwinDiscuss 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 aShow how natural selection could change a
populationpopulation
New VocabularyNew Vocabulary

Selective breeding, Artificial selection, NaturalSelective breeding, Artificial selection, Natural
selection, Evolutionselection, Evolution

2. Charles DarwinCharles Darwin boardedboarded
the HMS Beaglethe HMS Beagle inin 18311831..
Most believed the worldMost believed the world
was aboutwas about 6,0006,000 years old.years old.
During the shipDuring the ship’s five year’s five year
voyage, Darwin madevoyage, Darwin made
extensive collections ofextensive collections of
rocks,rocks, fossilsfossils, plants and, plants and
animals.animals.
He also read Charles LyellHe also read Charles Lyell’s’s Principles ofPrinciples of
GeologyGeology – a book proposing the Earth– a book proposing the Earth
waswas millionsmillions of years old.of years old.
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

3. In 1835, the Beagle arrived in theIn 1835, the Beagle arrived in the
Galapagos Islands off the coast of SouthGalapagos Islands off the coast of South
America.America.
Darwin began to collect mockingbirds,Darwin began to collect mockingbirds,
finches, and other animals on thefinches, and other animals on the fourfour
islands.islands.
He noticed that theHe noticed that the differentdifferent islandsislands
seemed to have their own, slightlyseemed to have their own, slightly
differentdifferent varietiesvarieties of animals.of animals.
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection
HMS BeagleHMS Beagle

4. Almost everyAlmost every
specimenspecimen
that Darwinthat Darwin
had collectedhad collected
on the islandson the islands
was new towas new to
EuropeanEuropean
scientists.scientists.
Darwin suspected populations from the mainlandDarwin suspected populations from the mainland
changedchanged after reaching the Galápagos.after reaching the Galápagos.
Galápagos IslandsGalápagos Islands
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

5. Darwin hypothesized thatDarwin hypothesized that newnew speciesspecies
could appearcould appear graduallygradually through smallthrough small
changeschanges in ancestral species.in ancestral species.
Darwin inferred that if humans couldDarwin inferred that if humans could
change species bychange species by artificial selectionartificial selection
(selective breeding), then perhaps the(selective breeding), then perhaps the
same process could work insame process could work in naturenature..
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection

6. Darwin called his theoryDarwin called his theory Natural SelectionNatural Selection
Developing the Theory ofDeveloping the Theory of
Natural SelectionNatural Selection
Natural SelectionNatural Selection
He reasoned that,He reasoned that,
given enough time,given enough time,
natural selection couldnatural selection could
modifymodify a populationa population
enough to produce aenough to produce a
new species.new species.

7. Basic Principles of Natural SelectionBasic Principles of Natural Selection

8. Darwin publishedDarwin published On the Origin of SpeciesOn the Origin of Species
by Means of Natural Selectionby Means of Natural Selection in 1859.in 1859.
Today, biologists use the term evolution toToday, biologists use the term evolution to
definedefine changeschanges in groups of organismsin groups of organisms
throughthrough time.time.
DarwinDarwin’s theory of natural selection is’s theory of natural selection is
NOTNOT the same as evolution. Naturalthe same as evolution. Natural
selection is a means of explainingselection is a means of explaining HOWHOW
evolutionevolution works.works.
The Origin of SpeciesThe Origin of Species