In all of the social animals, the first and probably the most powerful force that maintains the social fabric is forced birth control resulting from conflict. A termite mound may contain millions of potentially reproducing individuals, but it actually contains only one male and one female who reproduce. All the others are sterilized. Each ant, honeybee, and bumblebee colony contains, for the most part, also only one female who reproduces (although several males may have mated with her). Numerically, most of the other colony members are also female, but they remain chemically sterilized as long as the reproducing female is present. Only when the egg-laying female wanes in her reproductive power can and do some of the others develop and lay eggs. If a second reproductive female should emerge while the first is still reproductively active, the younger female will be killed if she does not leave first. One can appreciate the logical necessity of this, because if all of the tens of thousands of females started to lay eggs, it would be impossible to accumulate any resources, and the home with millions would very quickly collapse in chaos. If the bees, or some other hypothetical animal, should by some miracle be able to tap into a new, unforeseen source of food to fuel their economy, they would experience a few halcyon days of growth, to delay the day of reckoning a little further into the future, but to produce in the process a vastly larger debacle.
These considerations concern reality, such as the power of gravity, the speed of light, and the nature of the atom, from which all sorts of inferences can be drawn about our world. Naturally, one has to wonder, since we know concretely how these natural laws apply to termites, bees, ants, and naked mole rats, how might they apply to us who now live in virtual safety from all predators and most diseases?
Given life in a good place, and no conscious effort to limit family size, a Homo couple could easily conceive and raise a dozen offspring. Traditionally in agricultural societies, where the couple had more offspring than they could retain, the eldest son inherited the home and the land, the daughters were married off, and the “spare” sons were forced to leave home to seek their fortunes and find a home elsewhere. Population control happened inadvertently through famine, war, and disease. However, we also applied some draconian solutions to control births, in perhaps novel but not necessarily fair or adequate ways. Mostly we instigated various mechanisms to limit sex. The medieval European custom of putting a lock on women’s genitals with a metal chastity belt was in parts of Africa substituted by clitoridectomy and/or stitching the vagina shut. In addition, we erect taboos against sex, which in some societies were enforced by threat of death. But the cultural methods focusing on controlling women’s wombs run up against resistance, and rightly so, and one has to wonder if there are also biologically evolved, less draconian mechanisms of reducing births under locally crowded conditions.
Is it possible that in some pre-agricultural bands of humans or pre-humans conflict was reduced and the society preserved by some of its members willingly forgoing reproduction? Is it only a wild speculation to imagine a nonfertile segment of the society who, rather than destructively procreating, are creatively aiding? Such neutering is the standard practice that has evolved in the eusocial insects, where as mentioned earlier some members forgo both sex and reproduction and devote themselves to the service and upkeep of the society. This also happens in naked mole rats, where most of the members are and remain sterile by practicing no sex, and they perform vital functions that benefit them and the rest. The Catholic Church, for instance, imposes the neutering option via sex prohibition culturally in its clergy, ostensibly in order to commit them totally to the institution instead of to a family. The church encounters difficulties in this approach, because it does not take human biology fully into account: the forgoing of sex is difficult in a primate for whom sex serves various functions aside from procreation, such as bonding. However, even sex elimination has been accomplished in some tight human societies, such as by castration in the court of a powerful monarch (which closely mimics the situation in social insects).
One could imagine a more benign solution, such as a tight-knit society where some of the individuals in it are sexually attracted to others of the same gender. They would be spared the arduous demands of child rearing and would instead be able to specialize, as bees do, on tasks that require a high degree of attention, learning, and expertise and that would then benefit the whole group. It could be adaptive, and, if so, there is reason to suspect that the frequency of it would depend on stimuli resulting from environmental pressures. I do not know if this scenario is, was, or will be an adaptation in any animal. It can be. But, if so, it would not be in birds, in which sex is perfunctory. It would be in a species that is highly sexed and in which sex is related less to procreation than to recreation. It would be a species with small social groups that compete against one another not by physical force but by intellectual know-how. Such an adaptation is a theoretical possibility, and the bonobo and humans might be possible candidates.
Our genome is highly sensitive to the environment to which it is exposed. As we know from migratory locusts (to give but one of thousands of examples) and many other insects, birds, and mammals, environmental stimuli affect the timing and the kinds of hormones released into and circulating in the blood. Hormones affect behavior, physical development, and other physiological functions, because they control the genetic code and its output. Environment affects the fetus and the developmental trajectory after birth in any of a number of ways that become linked to promote survival. If groups compete against one another, and humans have probably been doing that as far back as we have existed, one group where resources can be used for innovation rather than procreation may do better than another where surplus reproduction brings it to the brink of exhaustion and subsistence living. Birth control for humans—in some cases in the form of chemicals, methods that are another totally new thing on the face of the Earth—in the long term may work to counter the otherwise inevitable collapse.
PART III
HOMING IMPLICATIONS
The tie that binds in homing is attachment to place. Yet not all animals are place-bound; some do not attach themselves to any place at all. Instead, they are innately and inflexibly bound to massive numbers of others of their own species. They seek out, orient, or “home” to others that, when en masse, become to them the main relevant feature of their environment. For them, the crowd is, wherever it may be, a place of refuge, as much as a forest is to a whitetail deer, or a field is to a meadowlark.
To many pelagic fish species inhabiting the vast featureless space of the open ocean there is little else to orient to; they have no choice. They swim in huge schools. That behavior of using each other as a reference, of homing “to the herd,” has evolved as a survival strategy in many animals. It doesn’t always work, though, because every strategy in one evolves into a counter-strategy in another; baleen whales capitalize on fishes’ herding instinct to catch them. In response to danger, the fish react by herding ever closer to each other, and in the presence of one of their greatest predators, a whale, which blows a circular bubble net around them from beneath, the bubbles then herd the fish, and they soon know nothing about the whale and only herd ever closer to each other. With its gigantic maw equipped with pleated plates, the whale then ingests the whole herd in a gulp. Had they each stayed separate, the whale would not have been a threat.
The In and Out of Boundaries
Good fences make good neighbors.
—Robert Frost, “Mending Wall”
BOUNDARIES ARE NECESSARY FOR ANY LIFE. AT THE CELLULAR level these are membranes. They separate the chaos of the external environment so that the intricate structure and biochemistry within can be built and maintained. The almost unimaginably complex and elegant chemistries of energy metabolism, genetics, and reproduction could not have come into existence, or be long maintained, without boundaries that selectively admit and exclude matter. And like any entity evolved to maintain itself, a home is also a bounded area. This truism does not, however,
preclude the equal necessity for “leakage” to allow for new circumstances as a compromise and an investment for the future.
Nowhere did the opposing functions of home boundaries—to keep the life-threatening out and the life-promoting in—seem more obvious to me than in the story of four American chestnut trees, Castanea dentata, that I purchased as seedlings and planted in the spring of 1982. They are descendants of magnificent ancestors that, with a diameter of three meters, grew to be over thirty meters tall. Billions of these trees once graced the North American forest from Maine to Mississippi, and their nuts fed the passenger pigeons, turkeys, bears, and whitetail deer.
Chestnut seeds fall to the ground and can’t spread thousands of kilometers by the wind as those of dandelions or poplar trees do, and I saw my four seedlings as a potential baby step toward bringing chestnuts back “home” to a tiny corner of their former range. I planted them in the woods next to my cabin, where I hoped they might be spared from contact with the Asian chestnut blight fungus that was first noted in the Bronx Zoo in 1905. It had been imported from perhaps one or several Asian chestnuts or chestnut trees (which are resistant to the fungus). There was no cellular barrier to the fungus released from Asia in the American tree counterparts, and it spread like wildfire through the forests all across North America. But there were now no more infected chestnut trees in western Maine from which these trees could be infected, so perhaps the seedlings would be protected from infection simply by the boundary of physical isolation. In addition, they were advertised to be from stock that had some immunity to the fungus as well.
The seedlings grew well after I had cleared the competing trees and brush from around them. They had light, and against the usual great odds facing all seedlings in any forest, they did survive the first dangers faced by most young trees—the browsing by hares, porcupines, deer, and moose.
About twenty years later, I noticed something grand: near the end of July the topmost branches of the then-over-six-meter-tall trees were resplendent with white blooms. The trees’ flowers have a funky carrion-like smell and attract swarms of flies and beetles. Nevertheless, I did not expect pollination (and hence viable seed), because genetic barriers to inbreeding between these four individuals from one source seemed likely, and there was no possibility for them to receive foreign pollen. Cross-pollination in plants is like sex in animals. It is one of those necessary immediate inefficiencies that scramble the genes to create variety. Perhaps the original American chestnuts were locally efficient, but they had forgone the diversity that could otherwise have saved them; they were uniformly susceptible to the Asian fungus. However, in the fall my trees had fruit hanging from their branches.
The fruit of the American chestnut tree, right after opening to release the three nuts it contains.
An American chestnut fruit is a ball (often called a “burr”) about five centimeters in diameter and resembles a hedgehog because it is covered in a thicket of sharp spines. As I had expected, none of these fruits that were soon scattered all over the ground the first few years that the trees bloomed contained nuts (i.e., seeds). Instead, like empty candy bar wrappers, each burr held only the shells of three putative nuts, indicating that they had not been pollinated.
The four trees themselves now faced problems as well, though not immediately from the fungus. Porcupines had practically de-limbed and girdled two of the trees within literally an inch (of intact bark) of their lives. I nailed metal flashing around their trunks to serve as a boundary that would prevent the porcupines from climbing and reaching the limbs. Luckily, the badly damaged trees still sent out healthy new shoots, and in a year or two they were recovering by growing new limbs. The trees now, at the age of thirty-two years, are growing faster than ever, and the largest has a height of 55 feet (17 meters) and a breast-high of 53 inches (135 centimeters). They flower every summer and bear fruits with seeds in late October.
As I contemplated the metal exclusion device for defense of the trees from porcupines, it was clear to me that the tree had invented its own mechanical means for protection, but mostly for its delicious, nutritious nuts. Its large seeds are far more prized as food by animals than its bark, and they are enclosed by a wall of spears. A credible boundary to the delicious nuts is necessary and must be relatively, but not absolutely, secure, not only because through evolution every strategy is likely to be met by a counter-strategy, but also because this tree species needs animals to disperse its seeds (nuts). But if so, the dispersing animals must be able to eat them, too, or else they would not bother to pick them up to hide them to eat later. According to the old saying “The acorn doesn’t fall far from the tree,” acorns and chestnuts do fall close to the trees, but they generally can’t grow up there. Soon after a young tree starts to grow under its parent, it will become starved for space and light. We now know that part of the solution is birds. Henry David Thoreau (Journal, vol. XIV, 1906) was one of the first naturalists to understand this; he wrote, “I have often wondered how red cedars could have sprung up in some pastures which I knew to be miles from the nearest fruit-bearing cedar, but it now occurs to me that these and barberries, etc. may be planted by the crows and other birds.” Blue jays and squirrels presumably plant acorns and beechnuts. But I did not know if both, one, or either of them also plants chestnuts.
To see how the tree protects its seeds from being eaten, yet manages to get them planted, required watching.
It’s mid-October 2010, and the sugar maples still carry golden foliage while the red maples and ash have shed their leaves, but the chestnut trees still have bright green leaves and hundreds of green fruits hanging from their branches. Within days, the fruits, each containing three nuts packed side by side, will start to open and be released. I knocked down several low-hanging fruits and smashed them open with a hammer, surprised to find plump (as opposed to thin, empty-hulled) seeds. A total of 400 fruits yielded 920 filled seeds (out of a possible 1,200). The flowers had apparently been pollinated after all. Many more fruits were under the trees on the ground. These all had empty seeds, the expected spontaneous abortions of the unpollinated female flowers.
After two days of a strong north wind that whipped the branches about, the rest of the fruits were still not dislodged from the trees, but only four days later, on October 18th, most of the chestnut fruits that were on the trees were finally opening. The four petal-like flanges of each fruit curled their velvety inside surfaces outward, offering their previously guarded nuts. (I do not know how they accomplish this movement of opening; I experimented to test several hypotheses but got no answer.) Blue jays were hopping from branch to branch, searching for the opening fruit and grabbing exposed nuts. They flew far into the distance, presumably to eat or cache, but if they did cache them it was too far away for me to see them do it. Corvid birds routinely cache food, and blue jays are no exception. Ravens dig a hole with their bills, insert the food, then cover it up by using the bill to scrape nearby soil or snow over it, and/or they pick up nearby debris such as leaves and place it over the spot. I had once seen scrub jays (in Oregon) do almost the same thing, but instead of digging a hole, they jackhammered the peanuts into the soil before covering them, much as ravens do. There would be no way for me to know if these blue jays had cached seeds, unless they did not retrieve them all and some of them sprouted trees.
The next year, 2011, hosted a huge masting event of the beech trees (close relatives of these chestnuts) in the New England forests. There had been no beech fruiting for sixteen to twenty years (based on aging the many hundreds of baby beeches), but there was also a record acorn crop. During the first week of October before the chestnuts were ripe, there seemed to be a “highway” of blue jays flying up and down my hill toward and from the beech grove by my cabin. Viewing from a tall spruce tree, I could see how far the jays were flying long after they left carrying the beechnuts, but I could not determine their destination, only the direction. Although jays in the trees picked beechnuts (each fruit contains two triangular seeds),
they ignored the nearby still-ripening chestnuts. But even after the chestnuts were ripened, the jays still ignored them, possibly because the beechnuts were more abundant, easier to get, or maybe easier to crack open to eat.
The blue jays I saw on the chestnut trees never tried to hack open a chestnut fruit, and I wondered if the nuts/seeds themselves, which have a hard leathery coat, may be impenetrable to them. When the next year a blue jay started coming to my bird feeder filled with black sunflower seeds, I had an opportunity to find out. I placed fifty chestnuts in the feeder among the sunflower seeds (which the jay had been hauling off for days). The jay immediately took the chestnuts in preference to the sunflower seeds, and in twenty successive visits to the feeder it took them all. Three times the bird flew with a single nut up onto a branch, held it to the branch with its feet, hammered it open in about a minute, and ate the contents. Clearly, this jay preferred chestnuts to sunflower seeds, and it had no problem opening them. However, when offered many at once, it appeared to try its best to haul them off quickly, presumably to cache.
I added more nuts and continued to try to find out how many a jay takes when it flies off into the distance for presumed caching trips. On average, this jay took three nuts per trip. It flew either low into the nearby woods with nuts, or high up into the tiptop of a tree at the edge of the clearing to pause there briefly, and then launch into the distance over the forest. It flew usually several successive trips in the same direction, and then switched, and for another several nut-hauling trips it left in another direction. But why would it fly so far to cache nuts? Does that give it the time to consolidate memory for a specific location? Do longer flights to and from a cache site make the location more memorable than a bunch of close-by scatter hoards? If so, the long flights must be “worth it,” and larger seeds would have a better chance to occupy new territory and also have more resources in them to get a head start in growth.
The Homing Instinct Page 21