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Evolutionary theory is a collection of scientific facts, observations, and hypotheses that helps explain the diversity of life Evolution (change over time) is the process by which modern organisms have descended from ancient organisms

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During his travels Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changed over time Whenever Darwin went ashore, he collected animal and plant specimens to add to a collection these helped support his theory Charles Darwin contributed greatly to the understanding of evolution Darwin s observations started when he joined the crew of the H.M.S. Beagle this allowed him to travel the world

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Most organisms were well suited for their environment There were different ways organisms reproduced depending on where they lived Darwin noticed certain patterns in diversity

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In some places, the habitat seemed correct for a certain species, yet they did not live there Even with similar environments, different areas could house different animals

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Some fossils looked similar to current living organisms Some fossils looked nothing like Darwin had seen before what happened to these species? Darwin also collected fossils which were important to support his theory Fossils = the preserved remains of ancient organisms

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Even though the islands were close together, they had very different climates Darwin noticed that land tortoises varied in predictable ways from one island to another and that just by the shell he could tell which island the tortoise came from While visiting the Galapagos Islands Darwin was greatly influenced

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Lonesome George

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Galapagos Clip

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The Bishop of Panama documented the officially first visit to the islands in 1535 After leaving, they sent word to King Carlos V of Spain, telling of the strange and foolishly tame wildlife and the numerous galapagos (giant tortoises), and the name stuck. The islands appeared on the map late in the 16th century as the "Insulae de los Galopegos". In 1546, a group of insubordinate soldiers of Pizzaro attempted what might have been South America's first coup d'etat. With their limited maritime skills, the ruffians attempted to arrive at the islands by sight. Peering through fog and carried by currents, they felt as though the islands themselves were moving, that they were enchanted and named them "Las Islas Encantadas."

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Many used the islands into way station and ports of call. The buccaneers were not the only to use the islands as bases for operations. In the 1800's, as South America became increasingly independent of Spanish rule and open to trading, mercantile vessels such as whaling ships came to the islands, especially Floreana. In 1807, Galapagos received its first resident. Irishman Patrick Watkins arrived on the island of Floreana marooned at sea. For two years he lived from growing vegetables, sometimes trading them with passing whaling ships for rum. Eventually he stole a ship's longboat, taking some of the sailors with him, however only he arrived at Guayaquil on the continent. 1959, one hundred years after the publication of Origin of the Species, Ecuador declared the islands its first national park, preserving whatever land that was not already settled for protection.

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Darwin started to wonder if animals living on different islands had once been members of the same species? Darwin also collected a variety of specimens of finches while in the islands, but made no major conclusions about them initially Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands

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The traditional view at the time was that the Earth and its creatures were only created a few thousand years ago and nothing had changed Fossil records started to challenge this view just before Darwin left for his travels

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Some scientists then said that there were several periods of creation, and each one was preceded by a catastrophic event that killed most living organisms Darwin realized his observations did not fit into that idea of thinking

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During Darwin s time, scientists made a new suggestion that the Earth was very old & changed slowly over time Two scientist, James Hutton and Charles Lyell helped recognize that Earth is millions of years old, and the processes from the past are the same processes that operate now

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Hutton was a geologist that published work about the geological forces that shaped the Earth Natural forces (wind, rain, heat & cold) can all shape the rocks

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Lyell was also a geologist and said that past events can be explained by processes that can actually be observed because they are still occurring Volcanoes, erosions, and earthquakes are the same now as they were in the past

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Given this new understanding of geology, Darwin was influenced in two ways If Earth can change over time, could life change as well? If Earth s changes are slow, would changes to life be slow too?

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The same year Darwin was born, Lamarck published his hypothesis that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. (use it or lose it!) Jean-Baptiste Lamarck was one of the first scientists to recognize that living things changed over time and that all species are descended from other species

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Part of Lamarck s idea was that organisms tried to move toward perfection which is why they acquired new traits to make them more successful Lamarck thought that acquired traits could be passed on to offspring Ex. If you went tanning and were very tan, you would have a very tan baby.

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Malthus said that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone Darwin was also influenced by the work of an English economist, Thomas Malthus

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Darwin realized this reasoning applied to other plants and animals even more so because they usually produce many more offspring than humans do

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Section 15-3: Darwin Presents His Case

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An essay from Alfred Wallace, another naturalist, summarized the ideas Darwin had been thinking about for 25 years and helped push him to publish his work Darwin finally published On the Origin of Species and proposed that natural selection was a mechanism for evolution

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Darwin learned that some of this variety was heritable passed from parents to offspring An important insight for Darwin was that members of each species vary from one another in important ways

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In artificial selection, nature provided the variation, and humans selected those variations that they found useful Darwin argues that this variety was important and that breeders could use heritable variation to improve livestock & crops

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Darwin compared artificial selection to nature and developed a hypothesis to explain how evolution occurs: the struggle for existence means that members of each species compete regularly to obtain food, living space, and other resources

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Adaptations make organisms more suited to their environment and better able to survive Adaptations can be structural characteristics, physiological processes, or even behaviors Fitness = the ability of an individual to survive and reproduce in its specific environment Fitness seemed to be the result of adaptations

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In survival of the fittest, individuals that are better suited to their environment survive and reproduce most successfully Natural selection is another term for survival of the fittest

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Natural selection results in changes in the inherited characteristics of a population these changes increase a species fitness in its environment Natural selection cannot be seen directly just as changes in a population over time

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Natural selection produces organisms with different structures, niches, and habitats as the environment changes In decent with modification, Darwin suggested that each living species has descended, with changes, from other species over time

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If you go far enough back, there should be a common ancestor to all living things this is known as common decent A single tree of life links all living things This idea implies that all living organisms are related to each other

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Darwin argued that living things have been evolving on Earth for millions of years. Evidence = the fossil record, geographic distribution, homologous structures, and similarities in embryology.

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Arms, wings, legs, and flippers are similar in structure and function, however they have been adapted in different environments Another piece of evidence was the anatomical similarities among body parts of animals with backbones

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Homologous structures = structures that have different mature forms but develop from the same embryonic tissues Homologous structures can help scientists group animals according to how recently they shared a common ancestor

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Some homologous structures do not serve important functions and may even be reduced in size these are known as vestigial organs Ex. Whales pelvis; Wisdom teeth

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Some variation is heritable Usually more offspring are produced than can survive Because more offspring are produced, they compete for limited resources Organisms best suited to their environment will survive Natural selection causes change over time Species are descended with modification from a common ancestor Summarizing Darwin s Theory