Chapter 15: Darwin’s Chapter 15: Darwin’s Theory of EvolutionTheory of Evolution

Charles Robert Darwin (1809-Charles Robert Darwin (1809-1882)1882)

““nothing in biology makes sense except in the nothing in biology makes sense except in the light of evolution”-Theodosius Dobzhanskylight of evolution”-Theodosius Dobzhansky

EvolutionEvolution

On the grandest scale, is all the changes that On the grandest scale, is all the changes that have transformed life over time.have transformed life over time.

Essentially, it is the biological history of life on Essentially, it is the biological history of life on Earth.Earth.

Evolutionary TheoryEvolutionary Theory: A collection of facts, : A collection of facts, observations, and hypotheses about the observations, and hypotheses about the process by which modern organisms have process by which modern organisms have descended from ancient ones.descended from ancient ones.

15-1: The Puzzle of Life’s 15-1: The Puzzle of Life’s DiversityDiversity

► In 1831, a 22-yr-old Darwin set sail on In 1831, a 22-yr-old Darwin set sail on the the HMS BeagleHMS Beagle on a 5 year cruise on a 5 year cruise around the worldaround the world

►As a naturalist, he studied the geology, As a naturalist, he studied the geology, plants, and animals encountered on plants, and animals encountered on the voyagethe voyage

Darwin’s ObservationsDarwin’s Observations

►He observed an immense amount of He observed an immense amount of diversity in the South American plants, diversity in the South American plants, animals, and fossils animals, and fossils Many different ways of reproducing and survivingMany different ways of reproducing and surviving Life seemed well suited for the environmentLife seemed well suited for the environment Some fossils resembled modern life forms, some Some fossils resembled modern life forms, some

had no resemblancehad no resemblance► The Galapagos Islands- islands had similar The Galapagos Islands- islands had similar

life forms but varied in climate and life forms but varied in climate and vegetationvegetation Darwin inferred that the species on the different Darwin inferred that the species on the different

islands had once been part of the same mainland islands had once been part of the same mainland species species

The Galapagos TortoisesThe Galapagos Tortoises

15-2: Ideas that Shaped 15-2: Ideas that Shaped Darwin’s ThinkingDarwin’s Thinking

► Darwin’s voyage occurred during one of the Darwin’s voyage occurred during one of the most exciting periods in the history of most exciting periods in the history of Western scienceWestern science

► Explorers were traveling the globe, and great Explorers were traveling the globe, and great thinkers were beginning to challenge thinkers were beginning to challenge established views about the natural worldestablished views about the natural world

► At this time, most Europeans believed:At this time, most Europeans believed: Life was created in its complexity and has Life was created in its complexity and has

remained fixed (or unchanging) since this timeremained fixed (or unchanging) since this time The Earth was about 10,000 years old and also The Earth was about 10,000 years old and also

relatively unchangingrelatively unchanging

Early InfluencesEarly Influences►George BuffonGeorge Buffon (mid-1700s): French naturalist; (mid-1700s): French naturalist;

collected fossils and noticed similarities and collected fossils and noticed similarities and differences; suggests Earth is older than differences; suggests Earth is older than 10,000yrs10,000yrs

► James HuttonJames Hutton (1785): English Geologist; (1785): English Geologist; suggest geological forces that shape Earth’s suggest geological forces that shape Earth’s surface are slow and require long periods of surface are slow and require long periods of time (Earth must be millions of years old)time (Earth must be millions of years old)

► Jean Baptiste LamarckJean Baptiste Lamarck (1809): French (1809): French naturalist; Explains Buffon’s observations by naturalist; Explains Buffon’s observations by making a hypothesis that life evolves through making a hypothesis that life evolves through the the inheritance of acquired characteristicsinheritance of acquired characteristics

Lamarck’s HypothesisLamarck’s Hypothesis

Geological InfluenceGeological Influence

► On the voyage of the On the voyage of the BeagleBeagle, Darwin read the , Darwin read the writings of geologist writings of geologist Charles Charles Lyell (1833)Lyell (1833)

► Lyell proposed that the Lyell proposed that the geological processes that geological processes that shape the Earth’s surface shape the Earth’s surface today (erosion, deposition, today (erosion, deposition, earthquakes, etc.) are the earthquakes, etc.) are the same processes that shaped same processes that shaped the Earth in the pastthe Earth in the past

► Encouraged explaining the Encouraged explaining the past in terms of observable past in terms of observable present day processespresent day processes

A Mechanism for ChangeA Mechanism for Change

► When Darwin returned to When Darwin returned to England, he could no longer England, he could no longer accept the idea of accept the idea of unchanging lifeunchanging life

► He began contemplating a He began contemplating a mechanism for evolutionary mechanism for evolutionary changechange

► In 1838, he read the work of In 1838, he read the work of Thomas MalthusThomas Malthus (an (an economist who wrote an economist who wrote an essay on human essay on human populations)populations)

► Malthus suggested that Malthus suggested that human warfare, famine, and human warfare, famine, and disease would limit the disease would limit the growth of the populationgrowth of the population

Darwin Publishes His IdeasDarwin Publishes His Ideas► In 1844, Darwin wrote a 200-In 1844, Darwin wrote a 200-

page essay that outlined his page essay that outlined his idea, but did not publish it in idea, but did not publish it in fear of controversy and doubtfear of controversy and doubt

► Instead he spent the next Instead he spent the next decade collecting evidence to decade collecting evidence to support his ideasupport his idea

► Darwin received an essay Darwin received an essay from a young naturalist, from a young naturalist, Alfred Alfred WallaceWallace, in 1858 proposing , in 1858 proposing the same idea for evolutionary the same idea for evolutionary change with similar evidencechange with similar evidence

► In 1859, Darwin published his In 1859, Darwin published his book book On The Origin of Species On The Origin of Species by Means of Natural Selectionby Means of Natural Selection