Darwin's Theory of Evolution: Explaining Earth's Diversity

1. Chapter 15 Darwin’s Theory of Evolution

2. Section 15-1How do we explain the diversity of life on Earth? • Evolution – change over time. It is the process by which modern organisms have descended from ancient organisms. • Current scientific facts, observations and hypotheses all combine to create current evolutionary theory – which is a well-supported, testable explanation of the biological diversity on Earth.

3. Darwin’s History Charles Darwin • Born on Feb. 12, 1809 (same day as Abraham Lincoln). • Came from a family of doctors so he was sent to the University of Edinburgh but found surgery disturbing so he dropped out. • His father then sent him to Christ’s College, Cambridge to become a Anglican minister. He was more interested in natural history and the sciences and worked closely with professors that allowed him to be outside doing “field work”. Christ’s College, Cambridge

4. Voyage of the H.M.S. Beagle • Darwin was recommended to sail on the H.M.S. Beagle as a companion to the captain. • The voyage lasted 5 years and sailed around the world. Darwin eventually become the ship’s naturalist, collecting specimens wherever they went. • The most important place that influenced Darwin was the Galapagos Islands.

5. Darwin’s Observations – left him with questions 3 Main Observations 1. Patterns of Diversity – • Darwin noticed that species fit the environment where they lived. • But he was puzzled by where animals lived and didn’t live. • Question? No rabbits in Australia? No kangaroos in Argentina?

6. Darwin’s Observations 2. Living organisms and Fossils – • Darwin collected preserved remains of organisms called fossils. • Some fossils looked like current animals, others looked completely different. • Question: How were they related to living species?

7. Darwin’s Observations 3. Galapagos Islands – • Small islands located 1000km west of South America. • Even though the islands were close together they had very different climates.

8. Darwin’s Observations Examples: • 1. Tortoises – longer neck for sparse vegetation. Shorter neck where vegetation was more abundant. • 2. Finches – Darwin noticed that these birds have different shaped beaks • Question? Why

9. Conclusions: The journey home • Nothing influenced Darwin more than his visit to the Galapagos Islands. • Darwin did not understand the reason for the diversity but he observed that many animals and plants varied noticeably among the different islands of the Galapagos. • He began to wonder if they had once been members of the same species.

10. Section15-2 Ideas that shaped Darwin’s Thinking • Up until Darwin’s time most Europeans believed that life on Earth was only about 2,000 years old. • But during the 19th century, scientists were gathering information that suggested that Earth was very old.

11. Hutton and Lyell Hutton – geologist • Geologic processes form slowly so Earth was much older than 2,000 years. Lyell – geologist who wrote “Principles of Geology” • We must explain past events from what we see today. For example, earthquakes and volcanoes Based on these geologists Darwin asked himself 2 questions. 1. If Earth could change, could life also change? 2. For life to change it must take many, many years which would only be possible if Earth was old.

12. Lamarck – use and disuse - 1809 • Lamarack – said that use or disuse of “organs” caused organisms to gain or loose certain traits during their lifetimes and then they could pass them on to their offspring. • He used this to explain how a giraffe got a long neck – it stretched! What’s wrong with this?

13. Thomas Malthus 1798 • He said that if human populations continued to grow sooner or later there would be insufficient living space and food for everyone. • This influenced Darwin because he realized it applied to all plants and animals…..not all offspring can survive… • What factor determines survival and death?

14. Section 15-3 Darwin Presents His Case Darwin returned from the Galapagos and begin writing about his discoveries. He was troubled by what he saw and his understanding that species became modified so he shelved his manuscript and told his wife to publish it when he died. But in 1858, another scientist (Alfred Wallace) started publishing results that were similar to Darwin so in 1859 Darwin decided to publish his results in a book called “On the Origin of Species.”

15. Variation – Artificial Selection Darwin knew that variation was important….not unimportant defects. His evidence was in farming and animal breeders of dogs and horses. Breeders choose traits they wanted and bred for them. We call this Artificial Selection.

16. Evolution by Natural Selection Definitions: 1. struggle for existence – members of a species compete for resources 2. Fitness – ability to survive and reproduce 3. Adaptations – inherited characteristics that increase an organisms chance of survival.

17. Natural Selection – How it works! Steps V 1. Variation = organisms within a population differ O 2 . Organisms produce more offspring than can survive. C 3. Organisms compete for limited resources. S 4. Individuals best suited to their environment survive and reproduce most successfully and pass on their traits to offspring. (Very, Often, Cars, Speed)

18. Natural Selection Example

19. Evidence for Evolution 4 pieces of evidence 1. Fossil Record – transitional fossils show us intermediate stages. Example: horse and camel

20. Evidence for Evolution 2. Geographic distribution – similar environments on different continents yielded similar anatomies and behavior because they were exposed to the same pressures of natural selection. We call this convergent evolution. Example: Flightless birds Emu – Australia Rhea – South America Ostrich - Africa

21. Evidence for Evolution 3. Homologous structures –When organisms have the same structure that performs different functions. They come from the same embryonic tissue. Example: front limbs of animals Vestigial structure – being reduced or eliminated in size. Ex. wisdom teeth, appendix

22. Evidence of Evolution 4.Embryos – in the early stages of development, many vertebrates look similar providing evidence that they shared a common ancestor. (mutations don’t occur early in development or the embryo would die)