Why do we go to war? There are many answers, but part of this book concerns one of them: because war is an inevitable property of humankind, an inheritance from our distant ancestors, and as such it’s part of the interconnectedness of the biosphere throughout its long history. In other words, war is part of the symbiotic heritage of all life. Therefore we must look to coexisting populations and their interactions, historical as well as recent, human as well as other species’, if we ever want a serious answer to the question above. Behaviors akin to warfare are found in species across the entire spectrum of the animal kingdom, so it’s no surprise that humans exhibit them too.
Despite the ubiquity (and tacit inevitability) of population wars, a closer examination of some distantly related species reveals that there is as much interdependence in the biosphere as there is violence. The present is full of assimilations from populations of the past, and when we recognize some of these, it becomes apparent that there is hope for a less violent future for humankind. Hence the inevitability of population wars doesn’t mean that our future has to be violently catastrophic. In order to achieve such a result, however, humans have to come to terms with some basic facts of population biology, and we need to see a shift in consciousness away from some of our most deeply rooted prejudices and bad habits that have come from the rapid expansion of our species.
Today we exist as a globally distributed species with a particular nasty propensity: When we can’t see our enemies, we invent them. This illusory act of human nature allows us to justify attempts at eradicating, eliminating, or vanquishing other people or species. But such actions nearly always fail. A further goal of this book is to highlight those failures as a reason to take a fresh approach to one of the time-honored problems of human existence: defining “us” as distinct from “them.” This is ultimately a question of biology. How distinct are different groups of living things? I hope to show you that the answer is, A lot less than you previously thought. If I’m successful, you’ll see why we need to rethink the entire justification for war, not only the human military kind but also the thought of Darwin’s “war of nature” or “struggle for existence,” because war follows logically only from a notion of distinctness. If lines of distinction are blurred, whom (or what) are we fighting? In my view all types of conflict have to be recast in the light of coexistence and historical contingency. That is the message of this book.
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There are four traditional categories of species interactions that fall under the heading of symbiosis: parasitism, predation, mutualism, and commensalism. The first two of these are antagonistic in the short term. Parasitism, the familiar situation where one species infests, infects, or inhabits the bodies of another species, and predation, where one species uses another as its source of food, usually make for dramatic storytelling. Familiar examples of these antagonistic types of population war include lice inhabiting the hair of schoolchildren (parasitism) or Canadian lynx chasing and killing snowshoe hares (predation).
The first of the two less antagonistic relationships between populations is mutualism, where two species derive benefits from and provide benefit to each other. Both species give up something in order to accommodate the other. This can be seen, for instance, in many species of ants (leaf-cutters) in the tropics. Huge colonies composed of thousands of individuals create elaborate underground caverns as part of their communal nests. Inside these subterranean burrows are gardens where the ants deposit leaf fragments they have harvested from the surrounding forest. Fungi grow on the leaf fragments in the gardens, and the ants make a meal of their vegetative parts. The fungi are not killed in the process; they just keep producing the vegetative portion as the ants feed over time. The ants benefit from having a convenient and predictable reserve of food growing in their nests, but the elaborate burrow construction and huge effort it takes to cut leaves and cultivate the gardens is a cost they must endure in the relationship. The fungi benefit from having a safe haven protected from other scavengers and parasitic bacteria of the forest floor, but have only restricted opportunities (gardens) to grow, thereby decreasing their opportunities to feed on and expand to other areas of the forest.
Commensalism is the second type of less antagonistic relationship. A commensal species is one that derives benefits from another species but doesn’t inflict any costs on the other. An example of this is the remora, a strange fish with a specialized sucking organ on the top of its head that allows it to attach to another species (usually a shark). Remoras “hitch a ride” on their hosts without actually providing any help in locomotion, or any benefits to speak of. There are no known negative effects caused by their freeloading. Usually the commensal individual is so small relative to the mass of the host that no significant friction or drag is caused to hinder transport. Another example of commensalism is the presence of possums, raccoons, suburban coyotes, or even bears that regularly eat the trash we throw away. These species opportunistically feed on our refuse, and there seems to be little or no cost to us associated with their commensal activity.
One chore I enjoy is cutting the grass. It just so happens that our “grass” is an alfalfa field nearly four acres in size. Every spring and summer I resign myself to a few days of driving my old tractor, mowing the tall grass. It’s hot, loud, and dusty work, and I’m pretty tired of the process after a few hours, even though the end result (hay) is a good thing. However, my mowing has a bloody side effect. The land is full of different small animal species, and as the blades cut the alfalfa they inadvertently slice scores of creatures unable to escape from under the mowing deck. Most are insects, but occasionally a field mouse or a vole runs the wrong way and can’t escape in time. This massacre is a boon to the crows that live in our woods, and they quickly swoop in to feast on the corpses. The birds are loud and obnoxious, and sometimes I have to swerve to miss them. I’d rather they go somewhere else. But I also know that they enjoy having me cut the grass, sometimes running over what will become their next meal. The crows have a commensal relationship with me, just like all the suburban commensals I mentioned above. I tolerate the crows, but they benefit more from the relationship than I do.
It’s easy to see how someone might construe the antagonistic relationship between a predator and its prey, or a parasite and its host, as that of a victor (the predator or parasite) and the vanquished (the prey or host). It’s important to remember that if the host or prey is exterminated, then the population of parasites or predators can’t last for long. The ways in which species interact is a more complex process than most people realize. If you haven’t studied the subject it’s easy to misinterpret Darwin and imagine that the natural world is in a constant state of high-stakes conflict. At the very least you might imagine a world where one population regularly dominates another into extinction, either by eating it or taking away its vitality. However, extinction in nature does not often result from the direct actions of other populations. Instead there is a spectrum of symbiotic relationships.
Even the most antagonistic relationship results in an equilibrium over the long term, which for our purposes can be viewed as a compromise between species. This is most glaringly illustrated when an incompatible pair of species comes together in a predator-prey relationship. The classic studies of predators and prey in the wild show oscillations of size for both populations. When predators are abundant, they reduce the prey population. Lower numbers of prey mean a limit on the predator’s reproduction rates, and their population size soon falls. This in turn makes for fewer predators, so the prey population increases once again. Over time these fluctuations reveal a stable equilibrium between predators and prey.
~~Population Wars: A New Perspective on Competition and Coexistence -by- Greg Graffin
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