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The academic field of population genetics includes several hypotheses regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions. Diversifying selection is the hypothesis that two subpopulations of a species live in different environments that select for different alleles at a particular locus. This may occur, for instance, if a species has a large range relative to the mobility of individuals within it. Frequency-dependent selection is the hypothesis that as alleles become more common, they become less fit. This is often invoked in host-pathogen interactions, where a high frequency of a defensive allele among the host means that it is more likely that a pathogen will spread if it is able to overcome that allele.

There are many different ways to measure genetic diversity. The modern causes for the loss of animal genetic diversity have also been studied and identified.^[1][2] A September 14, 2007 study conducted by the National Science Foundation found that genetic diversity and biodiversity are dependent upon each other -- that diversity within a species is necessary to maintain diversity among species, and vice versa. According to the lead researcher in the study, Dr. Richard Lankauof, "If any one type is removed from the system, the cycle can break down, and the community becomes dominated by a single species."^[3]

1. ^ Groom, M.J., Meffe, G.K. and Carroll, C.R. (2006) Principles of Conservation Biology (3rd ed.). Sunderland, MA: Sinauer Associates. Website with additional information: http://www.sinauer.com/groom/
2. ^ Tisdell, C. (2003). Socioeconomic causes of loss of animal genetic diversity: analysis and assessment. Ecological Economics 45(3): 365-376.
3. ^ Study: Loss Of Genetic Diversity Threatens Species Diversity

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