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Transcript
Evidence For Evolution Darwin and His Observations Evolution ò Change in a kind of organism over time ò The process by which modern organisms have descended from ancient organisms Voyage of the Beagle Voyage began in 1831 Ñ England – New Zealand – Australia – South Africa – British Isles – South America – Galapagos Islands Ñ Darwin’s Observations ò Patterns of Diversity – Plants and animals seem suited to the environment they live in. Ex: Argentina and Australia have similar grassland ecosystems, but have very different animals. Also, England has similar grasslands but no Kangaroos. Why? Ñ Living Organisms and Fossils– Some of the fossils Darwin collected resembled organisms that were still alive, while others looked completely unlike anything ever seen. How were fossil species related to living species? Darwin’s Observations Ñ The Galapagos Islands– Although the Galapagos Islands are close together, the islands have very different climates. Ó Ó Ex: Darwin observed that the giant tortoises varied from one island to another. The shape of a tortoise’s shell could be used to identify which island a particular tortoise inhabited. Ex: Darwin noticed several types of small birds with differently shaped beaks. An Ancient, Changing Earth ò James Hutton and Charles Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present. Lamarck’s Evolution Hypothesis ò Tendency Toward Perfection – organisms are continually changing and acquiring features that help them live more successfully in their environments. ò Ex: over many generations, birds kept trying to fly, their wings increased in size, and they became more suited to flying. ò Use and Disuse – Organisms could alter the size or shape of particular organs by using their bodies in new ways. ò Ex: If a winged animal did not use its wings, the wings would decrease through generations and disappear. Lamarck’s Evolution Hypothesis cont… ò Inheritance of Acquired Traits - Acquired characteristics can be inherited ò Ex: If you spend your life lifting weights to build muscles, your children will inherit big muscles. ò Summary – Was Lamarck correct? ______________ Inherited Variation and Artificial Selection ò Heritable variation in organisms is caused by variations in their genes ò Genetic variation is found in wild AND domesticated species ò Plant and animal breeders use genetic variation to improve crops and livestock (largest hogs, fastest horses, etc) ò Artificial selection – nature provides the variation and humans select the variations they find useful. Evolution by Natural Selection ò The Struggle for Existence ò High birth rates and shortages of resources force organisms into a competition for resources (food, living space, etc). Evolution by Natural Selection ò Survival of the Fittest ò Fitness – ability of an individual to survive and reproduce in its environment ò Fitness is the result of adaptations (inherited characteristics that increase an organism’s chance of survival) ò Survival of the Fittest – individuals better suited to their environment survive and reproduce ò Natural Selection – results in changes in the inherited characteristics of a population, resulting in an increase in fitness. Evolution by Natural Selection ò Descent with Modification ò Species today look different from their ancestors. Each living species has descended, with changes from other species over time. ò This implies that all living organisms are related to one another ò Common Descent – all species living and extinct were derived from common ancestors. “Tree of Life” Evidence for Evolution ò The Fossil Record – By comparing fossils from older rock layers with fossils from younger layers, scientists could document the fact that life on Earth has changed over time. ò Cephalopods have changed their shape over time in very obvious ways Evidence for Evolution ò Geographic Distribution of Living Species – Species that live on different continents descended from different ancestors but, because some were living in similar ecological conditions, they were affected by natural selection in similar ways. Because of this, they ended up evolving certain features in common. Evidence for Evolution ò Homologous Body Structures – Structures that have different mature forms but develop from the same embryonic tissues are called “homologous structures”. ò Vestigial organs – believed to be remnants of body parts that are no longer seen as necessary. Evidence for Evolution ò Similarities in Embryology – Embryos of many animals with backbones are very similar, meaning the same groups of embryonic cells develop in the same order and in similar patterns to produce tissues and organs of all vertebrates. Darwin’s Theory of Evolution ò Individual organisms differ, and some of this variation is heritable ò Organisms produce more offspring than can survive, and many that do survive do not reproduce ò Because more organisms are produced than can survive, they compete for limited resources ò Individuals best suited for their environment survive, reproduce, and pass heritable traits to their offspring. This causes species to change over time ò Species alive today are descended with modification from ancestral species, forming a “tree of life”