Darwin’s Theory of Evolution Chapter 15

Humans share the Earth with millions of other kinds of organisms of every imaginable size, shape, and habitat. How did all these different organisms arise? How are all these organisms related? This great variety of living things is called biodiversity. What scientific explanation can account for the great diversity of life?

The answer is a collection of scientific facts, observations, and hypotheses that are known as evolutionary theory. Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. A scientific theory is a well-supported, testable explanation of phenomena that have occurred in the natural world.

Charles Darwin is the individual who contributed more to our understanding of evolution than anyone. He was born in England on Feb 12, the same day Abraham Lincoln was born -- and National Geographic has called his evolutionary theory, “The Greatest Idea That Anyone Ever Had.”

Voyage of the H.M.S. Beagle Shortly after completing his college studies, Darwin agreed to become a science officer on an around-the-world sailing journey aboard the H.M.S. Beagle. Wherever the ship anchored, Darwin went ashore to collect plant and animal specimens that he added to an ever-growing collection. At sea, he studied his specimens, read the latest scientific books, and filled many notebooks with his observations and thoughts.

Darwin was well-educated and had a strong interest in natural history. His curiosity and analytical nature were ultimately the keys to his success as a scientist. The outcome of his extensive investigations, both during and after his voyage, led him to propose a revolutionary hypothesis about the way life changes over time and a scientific explanation for the great diversity of life on this planet. That hypothesis is now supported by a huge body of evidence and has become the theory of evolution.

Much of the press mocked Darwin when he first published his ideas, but his hypotheses have stood the test of time and are now celebrated for their genius.

Darwin’s Observations on Patterns of Diversity On his journey he began to realize there are an enormous number of species on Earth. He was intrigued by the fact that so many plants and animals seemed remarkably well-suited to whatever environment they inhabited. He was impressed with the way so many organisms survived and reproduced offspring. He was puzzled by where different species lived and did not live. For example, why are there no rabbits in Australia despite plenty of habitats that would be perfect for them? Why no kangaroos in England? These patterns posed challenging questions that became even more complicated when he realized living animals were just part of the puzzle. In many places, he collected and studied the preserved remains of ancient organisms. Some of those fossils looked like organisms still living while others looked completely different from any creature he had ever seen. As Darwin studied fossils, new questions arose. Why had so many species disappeared and how were they related to living species?

The Galápagos Islands This archipelago lies approximately 600 miles west of Ecuador in the eastern Pacific Ocean and will forever be associated with the name Darwin. Of all the Beagle’s ports of call, the Galápagos was the most influential on Darwin’s development of his hypotheses.

Thoughts from the Galápagos Darwin noted that although they were close together, the islands had very different climates. Some were hot, dry, and nearly barren while others had greater rainfall with rich vegetation. Darwin was particularly fascinated with the land tortoises and marine iguanas he found there. He noticed that the tortoises varied in predictable ways from one island to the next and the shape of the shell could be used to identify which island a tortoise lived on. Darwin later admitted in his notes that he “did not for some time pay sufficient attention” to that observation.

Thoughts from the Galápagos Darwin also saw several types of small, ordinary looking brown birds hopping around for seeds. He collected many specimens, but did not find them particularly unusual or important. However, as he examined the birds, he noted they had differently shaped beaks. He thought some of the birds were wrens, some warblers, and some blackbirds, but he came to no other conclusions… at first.

Darwin observed that the characteristics of many animals and plants differed noticeably among the different islands of the Galapágos. Although Darwin did not immediately understand the reason for these patterns of diversity, he had stumbled upon an important finding. After returning to England, Darwin began to wonder if animals living on different islands had once been members of the same species. According to this hypothesis, these now separate species would have evolved from an original South American ancestor species after becoming isolated from one another. Was this possible? If so, it was an idea that would turn people’s view of the natural world upside down.

You will now create a new Doc in Google 1. At the top of the doc, put your first and last name, your class period, and “Chapter 15: Darwin’s Theory of Evolution” 2. Title the doc, “firstinitial_lastname_Ch15” (use your name, duh, lol) 3. Create a heading that says “15-1: The Puzzle of Life’s Diversity” 4. Under that heading, define the following words: evolution, theory, fossil 5. Next, answer the 5 questions of the 15-1 Section Assessment found on p. 372 in your Biology text. You must type the questions and your responses. 6. Do not share your Doc with me at this time, we will be adding more to it. 7. Move on to the presentation for 15-2