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7.3 Evolution of Species Key Ideas ► What factors have contributed to the diversity of species? ► How do new species form? ► How do scientists infer evolutionary relationships among species? ► What causes the extinction of species? A Variety of Species ► Over time, different environments and genetic variation have produced, through natural selection, the variety of organisms that exist today ► Habitat: specific environment that provides the things the organism needs to live, grow, and reproduce ► Genetic Diversity : organisms within the same species do not all have identical traits. ► Some genetic differences, or variations, may result from mutations in DNA or rearrangement of genes during meiosis ► All the genetic variations in a species make up the total “gene pool” of that species ► High variety in gene pools VS. Low variety Corn, cheetah How do new species form? ►A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits Geographic isolation – one of the main possible ways new species form. Kaibab squirrel Abert’s squirrel Inferring Species Relationships ► Scientists have combined the evidence from DNA, proteins structure, fossils, early development, and body structure to determine the evolutionary relationships among species ► Elephant and elephant shrew : the mouse-like elephant shrews are more closely related to elephants than rodents based on DNA comparisons. Extinction of Species ► Extinct: no members of that species are still alive. (Woolly mammoths) ► Extinction if caused by a change in a species’ environment. The members of the species may not have adaptations that allow them to survive and reproduce in the changed environment ► Climate change : climate change can destroy organisms’ habitats It has been the leading cause of extinction ► Adaptation and survival – environmental change does not always lead to extinction. Some organisms may have traits that help them survive in a changed env. Some Q’s to think about… ► What causes extinction? ► How can isolation lead to the formation of new species?