Evolution is the change in genetic composition of a population over successive generations, which may be caused by natural selection, inbreeding, hybridization, or mutation. Some types of evidence, such as fossils and similarities between related living organisms, were used by Darwin to develop his theory of natural selection, and are still used today. Others, such as DNA testing, were not available in Darwin's time, but are used by scientists today to learn more about evolution.
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Adaptations in PopulationsAdaptations often occur in organisms as a response to environmental changes. An adaptation is a genetic change, or mutation, that makes the organism better able to survive in its new environment. These mutations are a normal part of the variation that exists in any population.
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IsolationGeographic isolation is a term that refers to a population of animals, plants, or other organisms that are separated from exchanging genetic material with other organisms of the same species. Typically geographic isolation is the result of an accident or coincidence. The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced are sterile.
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Human ImpactHuman impact on biodiversity has largely been negative, although some types of human activity may have had a beneficial effect. As the human population has grown, so too has the amount of land required for food. The increase in the amount of cropland from 1950 to 1980 was greater than the growth in cropland from 1700 to 1850. A growing population also requires more land for transportation and housing. As environments such as the rain forests of the Amazon are converted to cropland or paved over, habitat is destroyed, and many species may be left without any place to live or they may even be driven to extinction. Some species have also been driven to extinction by hunting or overharvesting. Some species of fish, for example, have been overharvested and their populations are in rapid decline. there are a few examples of positive human impacts on biodiversity. Creating protected areas such as nature preserves, for example, has helped protect biodiversity or at least slow its loss. Managing fisheries and logging operations so that resources are only removed at a sustainable rate has also helped conserve some biodiversity.
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