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Biodiversity is the number and variability of genes, species, and communities in space and time (Norse et al., 1986; Wilson, 1988; Heywood and Baste, 1995). The fundamental question that has governed its study in modern times is Hutchinson's (1959): “Why are there so many kinds of animals?” In more recent decades, a somber subquestion has been added: How many species are dying every year (e.g., Wilson, 1992)?
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J. John Sepkoski (1997) studied this question.
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