The Meaning of Human Existence (8 page)

Plants of some species communicate by pheromones. At least they are able to read the distress of neighboring plants by responding with actions of their own. A plant attacked by a serious enemy—bacteria, fungus, or insect—releases chemicals that suppress the invader. Some of the substances are volatile. They are “smelled” by their neighbors, who make the same defensive response even though they themselves are not yet under attack. Some species are assaulted by
sap-sucking aphids, insects especially abundant in the north temperate zone and capable of wreaking heavy damage. The plant-generated airborne vapor not only stirs neighboring plants to secrete defensive chemicals, but also reaches small wasps that parasitize aphids, drawing them to the vicinity. A few species use yet another defensive line. The signals are transmitted from plant to plant along the strands of symbiotic fungi that entwine the roots and connect one plant to another.

Even bacteria order their lives with pheromone-like communication. Individual cells come together, at which time they trade DNA of special value to one or the other. As their populations increase in density, some species also engage in “quorum sensing.” The response is triggered by chemicals released in the liquid around the cells. Quorum sensing results in cooperative behavior and formation of colonies. The best studied of the latter process is the construction of biofilms: free-swimming cells gather, settle on a surface, and secrete a substance that surrounds and protects the entire group. These organized micro-societies are all around and inside us. Among the most familiar are the scum on unwashed bathroom surfaces and the plaque on your inadequately brushed teeth.

There is a simple evolutionary explanation for why our species has taken so long to comprehend the true
nature of the pheromone-saturated world in which we live. To start, we are too big to understand the lives of insects and bacteria without special effort. Also, it was necessary while evolving to the
Homo sapiens
level for our forebears to have a large brain, containing memory banks expansible to a size large enough to make possible the origin of language and civilization. Further, bipedal locomotion freed their hands, allowing the construction of increasingly sophisticated tools. Large size and bipedalism together lifted their heads higher than those of any animals other than elephants and a few exceptionally large ungulates. The result was a separation of eyes and ears from almost all the remainder of life. More than 99 percent of the species are too minute in size and bound to the earth far below our senses to receive our ready attention. Finally, our antecedents had to use the audiovisual channel to communicate, not the pheromonal. Any other sensory channel, including pheromones, would have been too slow.

In a nutshell, the evolutionary innovations that made us dominant over the rest of life also left us sensory cripples. It rendered us largely unaware of almost all the life in the biosphere that we have been so heedlessly destroying. That didn’t matter very much in early human history, when humans first spread over Earth in the early logarithmic phase of their population growth. Still present
in small numbers at that time, they only skimmed energy and resources from the abounding and unsmelled life of the land and sea. There was still enough time and enough room to tolerate a large margin of error. Those happy days have ended. We cannot talk in the language of pheromones, but it will be well to learn more about how other organisms do it, in order better to save them and with them the majority part of the environment on which we depend.

8

The Superorganisms

I
magine yourself a tourist in an East African park, binoculars raised, watching lions, elephants, and a medley of buffalo and antelopes—the iconic large mammals of the savanna. Suddenly one of the continent’s greatest and least understood wildlife spectacles of all springs from the ground a few meters in front of you. It is a colony of millions of driver ants emerging from their subterranean nest. They are excited, fast, mindless, a river of small, random furies. At first a teeming mob with no evident purpose, the ants soon form a column that lengthens outward, so densely packed that many of them walk over one another, and the whole comes to resemble a twisting, writhing bundle of ropes.

No living creature dares to touch the angry column. Every one of the foragers is ready to bite and sting furiously any intrusive object that might serve as food. Posted along the column are soldiers, big defense specialists
that stand on raised legs with pincer-shaped mandibles poised upward. The driver ants are well organized, yet they have no leaders. The vanguard consists of whichever of the blind workers happen to reach the front at the moment. These dash forward briefly before yielding to others that press from behind.

At twenty meters or so out from the nest, the point of the column begins to spread into a fan-shaped front, composed of smaller and then still smaller columns. Very quickly the ground in its path is covered with a network of columns and individual workers, hunting and seizing insects, spiders, and other invertebrates. The purpose of the foray now becomes apparent. The ants are universal predators, harvesting as many small prey as they can subdue and bring back to the nest as food. The columns also drag home entire or in pieces any larger animals unable to get out of their way—lizards, snakes, small mammals, and, it is rumored, occasional unguarded babies. There is good reason for the unrelenting ferocity of the driver ants. A multitude of mouths must be fed with a lot of food, and frequently, because if not, the whole system will soon collapse. The entire colony, foragers and homebound workers combined, consists of as many as twenty million sterile females. All are daughters of the thumb-sized mother queen, which not surprisingly is also the largest ant known in the world.

The driver ant colony is one of the most extreme superorganisms ever evolved. If as you watch it you blur your focus a little, it resembles a gigantic amoeba sending out a meters-long pseudopodium to engulf particles of food. The units of the superorganism are not cells, as they are in amoebas and other organisms, but individual, full-bodied, six-legged organisms. These ants, these organism-units, are totally altruistic to one another and coordinated so completely that they closely resemble the combined cells and tissue of an organism. When you see them in nature or on film, you cannot help describing the driver ant colony as “it” rather than “they.”

All of the fourteen thousand known species of ants form colonies that are superorganisms, although only a very few are as complexly organized or as large as the driver ants. For nearly seven decades, starting in boyhood, I’ve studied hundreds of kinds of ants around the world, both simple and complex. This experience qualifies me, I believe, to offer you some advice on ways their lives can be applied to your own life (but, as you will see, of very limited practical use). I’ll start with the most frequent question I’m asked by the general public: “What can I do about the ants in my kitchen?” My response comes from the heart: Watch your step, be careful of little lives. They especially like honey, tuna, and cookie
crumbs. So put down bits of those on the floor, and watch closely from the moment the first scout finds the bait and reports back to her colony by laying an odor trail. As a little column follows her out to the food, you will see social behavior so strange it might be on another planet. Think of the kitchen ants not as pests or bugs, but as your personal guest superorganisms.

The second most frequently asked question is, “What can we learn of moral value from the ants?” Here again I will answer definitively. Nothing. Nothing at all can be learned from ants that our species should even consider imitating. For one thing, all working ants are female. Males are bred and appear in the nest only once a year, and then only briefly. They are unappealing, pitiful creatures with wings, huge eyes, small brain, and genitalia that make up a large portion of their rear body segment. They do no work while in the nest and have only one function in life: to inseminate the virgin queens during the nuptial season when all fly out to mate. They are built for their one superorganismic role only: robot flying sexual missiles. Upon mating or doing their best to mate (it is often a big fight for a male just to get to a virgin queen), they are not admitted back home, but instead are programmed to die within hours, usually as victims of predators. Now for the moral lesson: although like almost all well-educated Americans I am a devoted
promoter of gender equality, I consider sex practiced the ant way a bit extreme.

To return, briefly, to life in the nest, many kinds of ants eat their dead. Of course that’s bad enough—but I’m obliged to tell you they also eat their injured. You may have seen ant workers retrieve nestmates that you have mangled or killed underfoot (accidentally, not deliberately, I hope), thinking it battlefield heroism. The purpose, alas, is more sinister.

As ants grow older, they spend more time in the outermost chambers and tunnels of the nest, and are more prone to undertake dangerous foraging trips. They also are the first to attack enemy ants and other intruders that swarm into their territories and around their nest entrances. Here indeed is a major difference between people and ants: where we send our young men to war, ants send their old ladies. No moral lesson there, unless you are looking for a less expensive form of elder care.

Ants that are ill move along with the aged to the nest perimeter, and even to the outside. There being no ant doctors, leaving home is not to find an ant clinic but solely to protect the rest of the colony from contagious disease. Some ants die of fungus and trematode worm infections outside the nest, allowing these organisms to disseminate their own offspring. This behavior can be easily misinterpreted. You may wonder, if you have seen
too many Hollywood films on alien invaders and zombies, as I have, whether the parasite is controlling the brain of its host. The reality is much simpler. The sick ant has a hereditary tendency to protect its nestmates by leaving the nest. The parasite, for its part, has evolved to take advantage of ants that are socially responsible.

The most complex societies of all ant species, and arguably of all animals everywhere, are the leafcutters of the American tropics. In lowland forests and grasslands from Mexico to warm temperate South America, you find conspicuous long files of reddish, medium-sized ants. Many carry freshly cut pieces of leaves, flowers, and twigs. The ants drink sap but don’t eat solid fresh vegetation. Instead, they carry the material deep into their nests, where they convert it into numerous complex, spongelike structures. On this substrate they grow a fungus, which they do eat. The entire process, from collection of raw plant material to the final product, is conducted in an assembly line employing a sequence of specialists. The leafcutters in the field are medium in size. As they head home with their burdens, unable to defend themselves, they are harassed by parasitic phorid flies eager to deposit eggs that hatch into flesh-eating maggots. The problem is solved, mostly, by tiny sister ant workers that ride on their backs, like mahouts on elephants, and chase the flies away with flicks of their hind
legs. Inside the nest, workers somewhat smaller than the gatherers scissor the fragments into pieces about a millimeter in diameter. Still smaller ants chew the fragments into lumps and add their own fecal material as fertilizer. Even smaller workers use the gooey lumps thus created to construct the gardens. The smallest workers—the same size as the anti-fly guards—plant and tend the fungus in the gardens.

There is one additional caste of leafcutter ants, comprising the largest workers of all. They have outsized heads swollen with adductor muscles, which close their razor-sharp mandibles with enough force to slice leather (not to mention your skin). They appear to be specialized to defend against the most dangerous predators, including especially anteaters and probably a few other sizable mammals. The soldiers stay hidden deep in the lower chambers, charging forth only when the nest is in serious trouble. During a recent field trip in Colombia, I stumbled on a way to bring these brutes to the surface with almost no effort. I knew that leafcutter nests are constructed as a giant air-conditioning system. Channels near the center accumulate exhausted, CO
₂
-laden air heated by the gardens and the millions of ants living on them. As the air is warmed, it moves by convection through openings directly above. At the same time fresh air is pulled into the nest through openings to channels
located around the periphery of the nest. I found that if I blew into the peripheral channels, allowing my mammalian breath to be carried down into the nest center, the big-headed soldiers soon came out looking for me. I admit that this observation has no practical use, unless you like the thrill of being chased by really serious ants.

The advanced superorganisms of ants, bees, wasps, and termites have achieved something resembling civilizations almost purely on the basis of instinct. They have done so with brains one-millionth the size of human brains. And they have accomplished the feat with a remarkably small number of instincts. Think of evolving a superorganism as constructing a Tinkertoy. With just a few basic pieces fitted together in different ways it is possible to manufacture a wide variety of structures. In the evolution of superorganisms, those that survive and reproduce the most effectively are the ones that dazzle us today with their sophisticated complexity.

The fortunate few species able to evolve superorganismic colonies have as a whole also been enormously successful. The twenty thousand or so known species of social insects (ants, termites, social bees, and wasps combined) make up only 2 percent of the approximately one million known species of insects, but three-fourths of the insect biomass.

With complexity, however, comes vulnerability, and
that brings me to one of the other superorganism superstars, the domestic honeybee, and a moral lesson. When disease strikes solitary or weakly social animals that we have embraced in symbiosis, such as chickens, pigs, and dogs, their lives are simple enough for veterinarians to diagnose and fix most of the problems. Honeybees, on the other hand, have by far the most complex lives of all our domestic partners. There are a great many more twists and turns in their adaptation to their environment that upon failing could damage some part or other of the colony life cycle. The intractability thus far of the honeybee colony collapse disorder of Europe and North America, which threatens so much of crop pollination and humanity’s food supply at the present time, may represent an intrinsic weakness of superorganisms in general. Perhaps, like us, with our complex cities and interconnected high technology, it is their excellence that has put them at greater risk.