While on his voyage around the world aboard the H.M.S. Beagle, Charles Darwin spent about one month observing life on the Galápagos islands. There, he encountered some unique animals. But these unique creatures were obviously related to ones he knew, namely finches and tortoises. And as he looked closely at them, he noticed they were not as different from each other as they first appeared.

15–1 The Puzzle of Life’s DiversityA. Voyage of the Beagle

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shellHood

Floreana

Santa Cruz

James

Isabela

Tower

B. Darwin’s Observations-Patterns of Diversity-plants and animals adapt over time to their environment. The Galapagos Islands brought this fact home to Darwin.

Living Organisms and FossilsStudying fossils show links between living organisms

and ones long extinct.

15–2 Ideas That Shaped Darwin’s ThinkingA. Hutton and Geological Change-Hypothesized that geological

forces changed the earth over millions of years.

B. Lyell’s Principles of Geology-Past processes that shaped the earth continue today.

Volcanoes continue to erupt throughout

the world, destroying and creating

simultaneously in gigantic explosions

of hot gas and molten rock.

C. Lamarck’s Evolution Hypotheses 1. Tendency Toward Perfection

2. Use and Disuse

3. Inheritance of Acquired Traits

D. Thomas Malthus-Populations grow slowly at first and then exponentially until all available resources are at maximum use. The population will then crash as organisms die off from disease and starvation.

"In October 1838, …I had begun my…inquiry, I happened to read …Malthus on Population, …being well prepared to appreciate the struggle for existence which everywhere goes on… it at once struck me that under these circumstances (what Malthus described)… favorable variations would…be preserved, and unfavorable ones…destroyed. The results…would be the formation of a new species….I had at last got a theory by which to work".

Charles Darwin, from his autobiography. (1876)Quoted to show Malthus tremendous

influence on Darwin’s ideas.

15–3 Darwin Presents His Case

A. Publication of On the Origin of Species-

Published in 1859-28 years after Darwin’s voyage on the Beagle

For those who want to know, here is the link to the on-line text of Darwin’s famous and controversial book.

Go ahead and read it for yourself.

http://www.literature.org/authors/darwin-charles/the-origin-of-species/

B. Inherited Variation and Artificial Selection 1. Members of each species vary from one another in

important ways. a. This inherited variation can be used by breeders

to create organisms with other characteristics.b. If breeders can “artificially select” the traits they

want, Darwin proposed that there was a “natural selection” in place on Earth.

c. This “natural selection” permitted only those individuals with inherited traits that allowed them to survive to reproduce and produce offspring.

Excellent link on Evolution:http://www.pbs.org/wgbh/evolution/

C. Evolution by Natural Selection 1. The Struggle for Existence

a. More offspring are born than can survive.2. Survival of the Fittest

a. Those offspring that can survive do so because their inherited variations in genes permit their survival

3. Descent With Modification• Natural selection produces organisms that

have different structures, niches, habitats. • Species today look different from their

ancestors.• Each living species has descended, with

changes, from other species over time.• Implies that all living organisms are related

to one another.

D. Evidence of Evolution1. The Fossil Recordhttp://www.pbs.org/wgbh/nova/id/transitional.html

2. Geographic Distribution of Living Specieshttp://www.flmnh.ufl.edu/cnhc/csl-maps.htm

3. Homologous Body Structureshttp://evolution.berkeley.edu/evosite/lines/

IIhomologies.shtml4. Similarities in Embryos

Fish

Chicken

Pig

Human

E. Summary of Darwin’s Theory– Individual organisms differ. These differences are

inherited– Organisms produce more offspring than can

survive.– There is competition for limited resources.– Individuals best suited to their environment

survive and reproduce most successfully. This process of natural selection causes species to change over time.

– Species alive today are descended from species that lived in the past.

F. Evolutionary Theory Since Darwin

• Scientific advances in many fields of biology, along with geology and physics, have confirmed most of Darwin's hypotheses.

• Important questions still remain:– How new species arise– Why do species become extinct. – How did life began on our planet.