Darwin’s Theory of Evolution Two major questions led to the theory of evolution by natural selection: 1. What scientific explanation can account for the diversity of life? 2. What can explain the similarities and differences between living organisms? Evolution by natural selection is the accepted scientific theory for answering these questions and many others in Biology. * a theory is a widely accepted and much tested explanation that ties together lots of observations in science.

Charles Darwin – Father of Evolutionary Biology - born February 12, 1809 - son of a wealthy doctor - interested in natural history - first studied medicine in college, but didn’t like it - degree in theology with plans to become a country pastor - in 1831 was hired to be naturalist on HMS Beagle sailed around the world to map coasts (esp. S. America) - whenever they put into a port Darwin got off boat and explored the lands and collected specimens - these specimens became support for his theory of Natural Selection

Figure 15–1 Darwin’s Voyage Section 15-1 Figure 15–1 Darwin’s Voyage Voyage of the Beagle – 1831 - 1836

Darwin’s Observations 1. Noticed how well adapted organisms are to their native habitats. - similar habitats had similarly adapted animals - grazing animals in grasslands (antelopes vs. kangaroos) - streamlining in aquatic mammals and fish 2. Wondered why animals were found where they were – why were kangaroos only in Australia and not in other good habitats? 3. What was the relationship between living animals and fossils? 4. Had animals on the different Galapagos Islands once been members of the same species?

Glyptodont of South America

What do fossils show or mean?

The Galapagos Islands were a very important stop for Darwin. - while there he was told that you could tell the island that a tortoise came from by looking at its shell. - he wondered why they would be different - Darwin’s Finches – a group of small birds that he thought were all different - his bird expert, John Gould, told him they were closely related species. - Darwin didn’t keep good records of which islands they came from, so took longer to figure out their relationships.

Giant Tortoises of the Galápagos Islands Section 15-1 Giant Tortoises of the Galápagos Islands Pinta Tower Pinta Island Intermediate shell Marchena James Fernandina Santa Cruz Isabela Santa Fe Hood Island Saddle-backed shell Floreana Hood Isabela Island Dome-shaped shell

Mr. Patrick’s Tortoise friend - 2005

Darwin’s Finches of Galapagos Islands Bill differences allow these birds to use different food sources. Lft. – Large Ground Finch Rt. – Small Ground Finch

Medium Ground Finch

Opuntia megasperma – Prickly Pear

Blue-footed Booby

Sea Iguana and Sally Lightfoot Crabs

Interest Grabber Section 15-2 My, How You’ve Changed! Prior to the 1800s, life scientists knew that living things changed over generations. They just didn’t know how these changes were brought about. 1. Divide a sheet of paper into two columns and title the first one Inherited Characteristics. Title the second column Acquired Characteristics. In the first column, list the characteristics that you believe you have always had. For example, you may have brown eyes or curly hair. 2. In the second column, list your acquired characteristics. For example, you may have learned how to play a musical instrument. 3. Which of the items in your lists do you think you might pass on to your children? Explain your answer.

Section Outline 15–2 Ideas That Shaped Darwin’s Thinking A. An Ancient, Changing Earth 1. Hutton and Geological Change 2. Lyell’s Principles of Geology B. Lamarck’s Evolution Hypotheses 1. Tendency Toward Perfection 2. Use and Disuse 3. Inheritance of Acquired Traits 4. Evaluating Lamarck’s Hypotheses C. Population Growth

15-2 Ideas That Shaped Darwin’s Thinking A. An Ancient, Changing Earth * most Europeans of Darwin’s day thought the Earth was about 6000 years old - scientists were gathering evidence of a much older Earth - James Hutton (1795) proposed that sedimentary rocks form slowly and that geological features such as mountains and valleys are the result of natural processes. - Charles Lyell’s Principles of Geology was read by Darwin during his Beagle trip. - proposed Uniformitarianism – geologists must explain past events by processes they can observe in the world today. - showed that Earth had changed – could life have changed also?

Pangea – the original land mass in the Theory of Plate Tectonics – broke into Gondwanaland and Laurasia

Movement of Earth’s Crust Section 15-2 Sea level Sea level Sedimentary rocks form in horizontal layers. When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers. As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed. New sediment is then deposited above the exposed older rock surface.

Lamarck’s Evolution Hypotheses Jean-Baptist Lamarck – French evolutionist - Proposed the Hypothesis of Evolution by the Inheritance of Acquired Characteristics - said organisms have an innate tendency toward perfection and urges that make them want to evolve. - Use and Disuse – organisms could cause the growth or reduction of a body part by using or not using it - Inheritance of Acquired Traits – traits developed during a lifetime could be passed on to offspring Lamarck was wrong, but his was a scientific hypothesis of evolution that other biologists built upon.

Figure 15–7 Lamarck’s Theory of Evolution Front claw enlarges because it is being used more. The acquired characteristic, a large claw, is passed on to the offspring. Male crab uses small front claw to attract mates and ward off predators Section 15-2

Population Growth Thomas Malthus – English economist - wrote about human population growth and that if it continued unchecked there would eventually be insufficient space and food for everyone. - felt only war, famine, and disease kept this from happening * Darwin applied Malthus’ principles to all of nature and wondered: - What causes the death of so many individuals? - What determines which survive to reproduce and which do not?

Interest Grabber Section 15-3 When Is a Flipper a Wing? All living things are related. Some relationships are easy to see— your pet cat may not roar like a lion, but it clearly resembles one. Other relationships are less obvious.

Interest Grabber continued Section 15-3 1. On a sheet of paper, construct a table that has five columns and six rows. In the columns, write the following heads: Animal Group, Example, Legs, Fins, and Tail. Then, place the following animal groups in their own row: Mammal, Bird, Fish, Amphibian, Reptile, and Insect. 2. Give one example for each group, and then fill in the information for that example. For Legs, write in the number of legs that each animal has. Do animals with fins have legs? Do animals with wings have legs? If so, how many? 3. Can you tell from your table if a fish is more closely related to a bird or to an amphibian? Explain your answer.

Section Outline 15–3 Darwin Presents His Case A. Publication of On the Origin of Species B. Inherited Variation and Artificial Selection C. Evolution by Natural Selection 1. The Struggle for Existence 2. Survival of the Fittest 3. Descent With Modification D. Evidence of Evolution 1. The Fossil Record 2. Geographic Distribution of Living Species 3. Homologous Body Structures 4. Similarities in Embryology E. Summary of Darwin’s Theory F. Evolutionary Theory Since Darwin

15-3 Darwin Presents His Case Publication of On the Origin of Species shortly after Darwin returned to England in 1836 he began notebooks about his ideas on the origin of species. built a convincing case, but was hesitant to publish for both personal and scientific reasons – had unanswered questions. 1858 he received a letter for A. R. Wallace that summarized Wallace’s ideas about evolution – they were the same as Darwin’s. Soon after this, Darwin’s and Wallace’s ideas were presented together 1859 Darwin published On the Origin of Species Discussed evolution and proposed Natural Selection as the process by which evolution happened.

Not Everyone Agreed with Darwin

Inherited Variation and Artificial Selection Darwin pointed out variation in the members of each species. - from breeders he knew that some of this was heritable variation - he discussed Artificial Selection through which breeders were able to develop new types of domesticated plants and animals by selecting among the variations present. - he proposed that nature is also able to select for traits that are beneficial to survival. - He recognized the struggle for existence that organisms have as they compete for life’s necessities – food, water, shelter, mates, etc - in this struggle organisms with slightly better traits would survive better and thus pass their traits to the next generation more often - good traits = Fitness = ability to survive and reproduce in its specific environment

Artificial Selection Darwin wrote first about something familiar. Proves species are not immutable.

Natural Selection - fitness is the result of adaptations, which are inherited characteristics that increase an organism’s chance of survival - can be anatomical, physiological, or behavioral - Evolution by natural selection then is the accumulation of adaptations over time by succeeding generations which make them better adapted to the local environment. - Survival of the Fittest = Natural Selection - as organisms adapt over time they change = evolve - Evolution is change over time and implies that all living things have a history of common descent.

Evidence of Evolution The Fossil Record - fossil = any preserved evidence of past life - Darwin saw fossils as the history of life on Earth - could document the fact of evolution – organisms in the past were different than those living in the world today - most (>90%) species that have ever lived on Earth have gone extinct - Transitional fossils – show characteristics which link two groups of animals - Archeopteryx, Pakicetus, Ambulocetus - are missing links until they are found - fossil record is incomplete and always will be – organisms rarely fossilize and those that do are rarely found

Evidence of Evolution Geographic Distribution of Living Species - Darwin wondered why the Finches on the Galapagos Islands were each a little different and why they were different from the most similar species in South America - Why were there large tortoises on many oceanic islands and yet they were all different? - Why were entirely different species of animals found in South America and Australia and yet in similar habitats species had similar adaptations? - Darwin explained all of this by organisms evolving characteristics that best adapted them to local environments - similar environments = similar adaptations for fitness

Figure 15–14 Geographic Distribution of Living Species Section 15-3 Beaver Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capybara NORTH AMERICA Muskrat SOUTH AMERICA Capybara Coypu

Evidence of Evolution Homologous Body Structures - structures which have different mature forms but develop from the same embryonic tissues - living organisms have many anatomical similarities that have been adapted to different forms and functions - limbs of all vertebrates have similar bones which develop from the same embryonic clusters of cells - close examination shows that similarities are greatest among most closely related species and allow biologists to judge how closely related organisms are. - vestigial organs – organs that are homologous to those in other species, but are not used by the organism that has them - human appendix, legs of some skinks

Figure 15–15 Homologous Body Structures Section 15-3 Turtle Alligator Bird Mammal Ancient lobe-finned fish

Evidence of Evolution Similarities in Embryology - early stages (embryos) of many vertebrates are very similar - the same groups of embryonic cells become the same adult structures in most vertebrates - control of development is by the same genes in each group, not only in vertebrates, but also across other phyla

Concept Map Section 15-3 Evidence of Evolution includes The fossil record Geographic distribution of living species Homologous body structures Similarities in early development which is composed of which indicates which implies which implies Physical remains of organisms Common ancestral species Similar genes

Summary of Darwin’s Theory * Individual organisms differ, and some of this variation is heritable. * Organisms produce more offspring than can survive, and many that do survive do not reproduce. * Because more organisms are produced than can survive, they compete for limited resources. * Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other organisms die or leave fewer offspring. This process of natural selection causes species to change over time. * Species alive today are descended with modifications from ancestral species that lived in the distant past. This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life.

This slide is intentionally blank. End of Custom Shows