Copyright Pearson Prentice Hall Evolution by Natural Selection Darwin compared processes in nature to artificial selection. By doing so, he developed a scientific hypothesis to explain how evolution occurs. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Struggle for Existence  Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall How is natural selection related to a species' fitness? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Survival of the Fittest  The ability of an individual to survive and reproduce in its specific environment is fitness. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection. In natural selection, the traits being selected contribute to an organism's fitness in its environment. Copyright Pearson Prentice Hall

Evolution by Natural Selection Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Descent With Modification  Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. Each living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evidence of Evolution What evidence of evolution did Darwin present? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evidence of Evolution Evidence of Evolution Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process include: the fossil record geographical distribution homologous structures similarities in early development, or embryology. Copyright Pearson Prentice Hall

EVIDENCE FOR THE THEORY OF EVOLUTION 1. Fossils Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Evidence of Evolution The Fossil Record  Darwin saw fossils as a record of the history of life on Earth. By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time. Copyright Pearson Prentice Hall

Fossils and Ancient Life The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The fossil record provides incomplete information about the history of life. Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out. Copyright Pearson Prentice Hall This Photo by Unknown Author is licensed under CC BY-NC-SA

Copyright Pearson Prentice Hall How Fossils Form How Fossils Form Most fossils form in sedimentary rock. Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall How Fossils Form Fossil Formation The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock. Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Paleontologists determine the age of fossils using relative dating or radioactive dating. Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Relative Dating In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock. Rock layers form in order by age—the oldest on the bottom, with more recent layers on top. Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Index fossils are used to compare the relative ages of fossils. An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Radioactive Dating  Scientists use radioactive decay to assign an absolute age to rocks. Radioactive dating is the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms in a sample to decay. Copyright Pearson Prentice Hall

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Mass Extinction Events Percentage of species extinct Geologic Time Scale Mass Extinction Events Percentage of species extinct 76% species 80% species 96% species The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods. 75% species