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Darwin's Theory of Evolution

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Greg Evans

on 27 February 2013

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Transcript of Darwin's Theory of Evolution

Darwin's Observations Ch. 15 - Darwin's Theory of Evolution 15.1 - The Puzzle of Life's Diversity What Scientific explanation can account for the diversity of life? 15.2- Ideas That Shaped Darwin's Thinking Darwin was greatly influenced by the work of other scientist (some of which were flawed), especially those studying the history of the Earth. Darwin Presents His Case Evolution, or a change over time, is a proposed theory by which modern organisms have descended from ancient organisms. A theory is a supposition or a system of ideas intended to explain something. Voyage of the H.M.S. Beagle Charles Darwin:
born Feb. 12, 1809
1831 he joined the crew of the H.M.S. Beagle for a voyage around the world
developed the theory of evolution
died April 19, 1882 While on his voyage Darwin made many observations of plant and animal life.
In 1 day in a Brazilian rainforest he collected 68 different beetle species. Patterns of Biodiversity Darwin was interested in the fact that so many organisms were so well suited for the environment they lived in.
He also wondered why some species lived in certain areas and not in others. Living Organisms and Fossils On his voyage Darwin collected many fossils. He noted that some resembled organisms that were still alive, while others were unlike anything he had ever seen. These observations brought about new questions such as:
Why had these species disappeared?
How were they related to living species? The Galapagos Islands Darwin was most influenced by this group of small islands west of South America. He was particularly intrigued with the marine iguanas and the land tortoises. The Journey Home While traveling Darwin thought a lot about his observations, specifically about how the plant and animal life varied greatly from island to island in the Galapagos. He began to wonder if animals on different islands that were similar had once been members of the same species. Was this possible? Hutton's Theory of Geological Change In 1795, James Hutton published his theory about geological forces that have shaped earth. He said that most geological changes happen slowly, over millions of years. Lyell's "Principles of Geology" Darwin was actually reading "Principles of Geology" while he was aboard the H.M.S. Beagle. In his book Lyell said that scientists must explain past events in terms of processes that they can observe. ie. erosion and volcanic eruptions While on his voyage Darwin actually observed a volcanic eruption and an earthquake. Darwin then asked himself: If the earth can change over time, could life change as well? Lamarck's Theory of Evolution 1809, Lamarck published his theory of how organisms change over time. Lamarck proposed three statements:
All organisms tend toward complexity and perfection.
Organisms can alter the size or shape of their bodies by using them in new ways.
Acquired characteristics can be inherited. Population Growth Thomas Malthus observed that babies were being born faster than people were dying. If the human population continued to grow unchecked then we would run out of food and space. Darwin reasoned that humans have fewer offspring than most other species, so how much more should this idea apply to them. He questioned:
What caused so many individuals to die?
What factor determined which ones survived to reproduce? Publication of "On the Origin of Species" Darwin filled multiple notebooks with notes and thoughts as he was on his voyage. He didn't publish these thoughts right away though because they challenged all of the fundamental scientific beliefs of his day. Darwin only published his thoughts because Alfred Russel Wallace was going to publish an essay on evolution. Natural Variation and Artificial Selection Darwin abandoned the idea of a perfect unchanging species. He said that differences among individuals of a species, is found in all types of organisms, this he called natural variation. Darwin made the most progress on his theory by studying English farmers and breeders. In artificial selection, nature provided the variation among different organisms, and humans selected those variations that they found useful. Evolution by Natural Selection The Struggle for Existence Members of each species compete to obtain food, living space, and other essentials Survival of the Fittest Fitness - the ability of an individual to survive and reproduce is a result of Adaptation - any inherited characteristic that increases the chance of survival Descent with Modification Evidence of Evolution The Fossil Record Darwin viewed the fossil record as a detailed record of evolution. Geographic Distribution of Living Species Sometimes in similar environments organisms had the similar structures and behaviors, and sometimes they didn't. Homologous Body Structures Structures that have different mature forms, but develop from similar embryonic tissues. Similarities in Early Development Summary of Darwin's Theory Individual organisms can differ from each other, some of this variation is inherited.
Organisms produce more offspring than can survive. You don't survive, you don't reproduce!
Members of each species must compete for limited resources.
Each organism has unique advantages and disadvantages.
Organisms that reproduce, pass on the traits that make them best suited.
Species change over time.
Species alive today have descended with some modifications from species that lived in the past.
All organisms are united in a single tree of life by common descent.
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