Bruce Bagemihl - Biological Exuberance

Like chaos theory, the Gaia hypothesis recognizes that phenomena that appear inexplicable at the level of an individual organism or population may be part of a larger, complex tapestry: a web of seemingly incongruous forces that interact to produce the flow of life, often in ways that are difficult to fathom. Nowhere is this idea better formulated than in the concept of biodiversity . Stated simply, this is the principle that the vitality of a biological system is a direct consequence of the diversity it contains: “as diversity increases, so does stability and resilience.” 103Traditionally, such diversity is thought of strictly in terms of number and types of species—that is, the physical composition of the system, usually expressed in terms of its overall genetic variety. Long-term studies of individual ecosystems have shown, for example, that the health and stability of a natural system is directly linked to the number of different species it contains. 104

However, variability in number of species is not the only way that biological diversity can be expressed. At all levels of the natural world, social and sexual diversity exists—in every type of animal, and between different species, populations, and individuals. As an example, consider just one group of birds, the sandpipers and their relatives. 105An enormous variety of heterosexual and homosexual mating and social systems are found among the more than 200 species in this group. We find monogamous pairings between birds of the same or opposite sex (Black-winged Stilts, Greenshanks); polygamous associations such as one male mating with more than one female (northern lapwings, curlew sandpipers) or one female mating with more than one male (jacanas), or bisexual trios in which two birds of the same sex bond with each other and with a third individual of the opposite sex (Oystercatchers); and “promiscuous” systems in which birds court and mate with multiple partners of the same or opposite sex without establishing pair-bonds, often involving communal courtship display grounds or leks (Ruffs, Buff-breasted Sandpipers). Even within a particular mating system such as heterosexual “monogamy,” there are many different variations: some species form lifelong pair-bonds (e.g., Black Stilts); others are serially monogamous, forming sequential pairbonds or mating associations with different partners (kentish plovers, sanderlings); others are primarily monogamous but form occasional polygamous trios (Golden Plovers). Some species have largely “faithful” pair-bonds, with birds rarely if ever copulating with individuals other than their mate (Golden Plovers), while in others nonmonogamous matings with birds outside of the pair-bond are routine (Oystercatchers). And even within a given species, there are variations between different geographic areas: lesbian pairs occur in only certain populations of Black-winged and Black Stilts, for example, while snowy plovers exhibit extensive geographic variation in their heterosexual mating patterns, ranging from monogamy to serial polygamy (and numerous versions of each). Within a given population, there is also diversity between individual birds. In Oystercatchers, for example, only some birds participate in homosexual associations, nonmonogamous heterosexual copulations, or serial monogamy, while extensive numbers of nonreproducing birds that do not engage in either heterosexual or homosexual activities are also found in most species. And finally, each individual bird may participate in a variety of sexual and mating behaviors during its lifetime. Among male Ruffs, for example, some birds are exclusively heterosexual for their entire lives, some alternate between periods of heterosexual and homosexual activity or engage in both simultaneously, other individuals participate primarily in same-sex activities for most of their lives, while still others are largely asexual. Similar examples could be furnished from virtually any other animal group, especially now that detailed longitudinal studies are beginning to reveal individual (and idiosyncratic) life-history variations in nearly all organisms.

Scientists are beginning to find evidence that this diversity in social and mating systems contributes directly to the “success” of a species. For instance, among great bustards (a large, storklike bird found in southern Europe and North Africa), flexibility in heterosexual mating systems gives the birds a greater adaptability, enabling them to cope with difficult or variable ecological conditions. 106And in some species, homosexuality itself appears to be associated with environmental or social changes, in ways that are suggestive but (so far) poorly understood. Male pairing in Golden Plovers, for example, is claimed to be more prevalent in years when severe winter snowstorms have “disrupted” heterosexual pairing, while female coparenting among Grizzlies appears to be characteristic of animals living in conditions of environmental or social flux. In Ostriches, homosexual courtships may be linked to unusually rainy seasons that alter the species’ overall sexual and social patterns. Likewise, same-sex pairs in Ring-billed and California Gulls are more common in newly founded colonies that are experiencing rapid expansion, while homosexual activities in Rhesus and Stumptail Macaques (and a number of other primates) are often associated with changes in the composition or dynamics of the social group. 107

Although the correlations between these factors need to be more systematically investigated—a linear, one-way, cause-and-effect relationship is surely not involved—they do suggest that sexual, social, and environmental variability may be closely allied. Specifically, the capacity for behavioral plasticity—including homosexuality—may strengthen the ability of a species to respond “creatively” to a highly changeable and “unpredictable” world. As primatologist G. Gray Eaton suggests, sexual versatility as both a biological and a cultural phenomenon in animals maybe directly responsible for a species’ success, in ways that challenge conventional views of evolution:

The macaques’ sexual behavior includes both hetero- and homosexual aspects as part of the “normal” pattern. Protocultural variations of some of these patterns have already been discussed but it is well to remember the extreme variation in behavior that characterizes individuals and groups of primates. This plasticity of behavior has apparently played a major role in the evolutionary success of primates by allowing them to adapt to a variety of social and environmental conditions…. The variability and plasticity of the behavior… suggests an optimistic or “ maximal view of human potentialities and limitations”… rather than a pessimistic or minimal view of man as a biological machine functioning on the basis of instinct. This minimal view based on the fang-and-claw school of Darwinism finds little support in the evidence of protocultural evolution in nonhuman primates. 108

This is not to say that such plasticity always has an identifiable “function” in relation to specific environmental or social factors (even though a few such “functions” can be discerned in specific cases, as we saw in previous chapters). Behavioral versatility is best regarded as a manifestation of the larger “chaotic ordering” or nonlinearity of the world, rather than merely a response to it. A broader synergy is involved, a pattern of overall adaptability that can be realized in ways that do not necessarily entail any literal “contribution” to reproduction or any straightforward “improvement” in an animal’s well-being. In other words, it is the presence of behavioral flexibility in a system that is as valuable, if not more so, than its actual concrete “usefulness” or “functionality.”