Biological Exuberance: Animal Homosexuality and Natural Diversity

According to Wilson (1992), approximately 1,032,000 species of animals are currently known to science, although the number of actually occurring species is undoubtedly much higher—on the order of 10-100 million—and there are many complexities in estimating the total number of species. For further discussion, see Wilson, E. O. (1992) The Diversity of Life, pp. 131ff (Cambridge, Mass.: Belknap Press); Wilson, E. O. (1988) “The Current State of Biological Diversity,” in E. O. Wilson, ed., BioDiversity, pp. 3-18. (Washington, D.C.: National Academy Press); May, R. M. (1988) “How Many Species Are There on Earth?” Science 241:1441—49.

31

Le Boeuf and Mesnick 1991:155 (Elephant Seal); see also Wilson, E. O. (1975) Sociobiology: The New Synthesis (Cambridge and London: Belknap Press). This figure is borne out by the data on homosexuality: the average number of observation hours for scientific studies in which homosexual behavior has been observed is approximately 1,050 hours (based on data from 47 species in which the number of observation hours has been recorded).

32

Marten, M., J. May, and R. Taylor (1982) Weird and Wonderful Wildlife, p. 7. (San Francisco: Chronicle Books). A somewhat more precise estimate of the number of species that have been adequately studied can be obtained for a subset of animals by using the Zoological Record (a comprehensive electronic database that indexes more than a million zoological source documents, including articles from over 6,000 journals worldwide, over the past 20 years). The Zoological Record for the period 1978-97 lists 825 mammal species in which at least some aspects of courtship, sexual, pair-bonding, mating-system, and/or parenting behaviors have been studied (the behavior categories in which homosexuality, if present, is likely to be found). Homosexual behavior has been documented in 133 of these species, or approximately 16 percent—comparable to the lower range obtained using the estimate of Marten et al. (The following subject headings/behavior categories indexed by Zoological Record were used in compiling this estimate: Courtship, Lek, Sexual Display, Precopulatory Behavior, Copulation, Mating, Pair Formation, Monogamy, Polygamy, Cooperative Breeding, Breeding Habits, Parental Care, Care of Young, Homosexuality).

33

See chapter 4 for further discussion of these factors.

34

For species that do not engage in “heterosexual” mating at all, e.g., parthenogenetic or hermaphrodite animals, see the next section.

35

Clapham, P. J. (1996) “The Social and Reproductive Biology of Humpback Whales: An Ecological Perspective,” p. 37, Mammal Review 26:27-49.

36