Authors: Stephen Jay Gould
The Reverend William Kirby, rector of Barham, and Britain’s foremost entomologist, chose to ignore the plight of caterpillars and focused instead upon the virtue of mother love displayed by wasps in provisioning their young with such care.
The great object of the female is to discover a proper nidus for her eggs. In search of this she is in constant motion. Is the caterpillar of a butterfly or moth the appropriate food for her young? You see her alight upon the plants where they are most usually to be met with, run quickly over them, carefully examining every leaf, and, having found the unfortunate object of her search, insert her sting into its flesh, and there deposit an egg…. The active Ichneumon braves every danger, and does not desist until her courage and address have insured subsistence for one of her future progeny.
Kirby found this solicitude all the more remarkable because the female wasp will never see her child and enjoy the pleasures of parenthood. Yet love compels her to danger nonetheless:
A very large proportion of them are doomed to die before their young come into existence. But in these the passion is not extinguished…. When you witness the solicitude with which they provide for the security and sustenance of their future young, you can scarcely deny to them love for a progeny they are never destined to behold.
Kirby also put in a good word for the marauding larvae, praising them for their forbearance in eating selectively to keep their caterpillar alive. Would we all husband our resources with such care!
In this strange and apparently cruel operation one circumstance is truly remarkable. The larva of the Ichneumon, though every day, perhaps for months, it gnaws the inside of the caterpillar, and though at last it has devoured almost every part of it except the skin and intestines, carefully all this time it avoids injuring the vital organs, as if aware that its own existence depends on that of the insect upon which it preys!…What would be the impression which a similar instance amongst the race of quadrupeds would make upon us? If, for example, an animal…should be found to feed upon the inside of a dog, devouring only those parts not essential to life, while it cautiously left uninjured the heart, arteries, lungs, and intestines,—should we not regard such an instance as a perfect prodigy, as an example of instinctive forbearance almost miraculous? [The last three quotes come from the 1856, and last pre-Darwinian, edition of Kirby and Spence’s
Introduction to Entomology
This tradition of attempting to read moral meaning from nature did not cease with the triumph of evolutionary theory in 1859—for evolution could be read as God’s chosen method of peopling our planet, and ethical messages might still populate nature. Thus, St. George Mivart, one of Darwin’s most effective evolutionary critics and a devout Catholic, argued that “many amiable and excellent people” had been misled by the apparent suffering of animals for two reasons. First, whatever the pain, “physical suffering and moral evil are simply incommensurable.” Since beasts are not moral agents, their feelings cannot bear any ethical message. But secondly, lest our visceral sensitivities still be aroused, Mivart assures us that animals must feel little, if any, pain. Using a favorite racist argument of the time—that “primitive” people suffer far less than advanced and cultured folk—Mivart extrapolated further down the ladder of life into a realm of very limited pain indeed: Physical suffering, he argued,
depends greatly upon the mental condition of the sufferer. Only during consciousness does it exist, and only in the most highly organized men does it reach its acme. The author has been assured that lower races of men appear less keenly sensitive to physical suffering than do more cultivated and refined human beings. Thus only in man can there really be any intense degree of suffering, because only in him is there that intellectual recollection of past moments and that anticipation of future ones, which constitute in great part the bitterness of suffering. The momentary pang, the present pain, which beasts endure, though real enough, is yet, doubtless, not to be compared as to its intensity with the suffering which is produced in man through his high prerogative of self-consciousness [from
Genesis of Species
It took Darwin himself to derail this ancient tradition—and he proceeded in the gentle way so characteristic of his radical intellectual approach to nearly everything. The ichneumons also troubled Darwin greatly and he wrote of them to Asa Gray in 1860:
I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.
Indeed, he had written with more passion to Joseph Hooker in 1856: “What a book a devil’s chaplain might write on the clumsy, wasteful, blundering, low, and horribly cruel works of nature!”
This honest admission—that nature is often (by our standards) cruel and that all previous attempts to find a lurking goodness behind everything represent just so much special pleading—can lead in two directions. One might retain the principle that nature holds moral messages, but reverse the usual perspective and claim that morality consists in understanding the ways of nature and doing the opposite. Thomas Henry Huxley advanced this argument in his famous essay on
Evolution and Ethics
The practice of that which is ethically best—what we call goodness or virtue—involves a course of conduct which, in all respects, is opposed to that which leads to success in the cosmic struggle for existence. In place of ruthless self-assertion it demands self-restraint; in place of thrusting aside, or treading down, all competitors, it requires that the individual shall not merely respect, but shall help his fellows…. It repudiates the gladiatorial theory of existence…. Laws and moral precepts are directed to the end of curbing the cosmic process.
The other argument, radical in Darwin’s day but more familiar now, holds that nature simply is as we find it. Our failure to discern a universal good does not record any lack of insight or ingenuity, but merely demonstrates that nature contains no moral messages framed in human terms. Morality is a subject for philosophers, theologians, students of the humanities, indeed for all thinking people. The answers will not be read passively from nature; they do not, and cannot, arise from the data of science. The factual state of the world does not teach us how we, with our powers for good and evil, should alter or preserve it in the most ethical manner.
Darwin himself tended toward this view, although he could not, as a man of his time, thoroughly abandon the idea that laws of nature might reflect some higher purpose. He clearly recognized that specific manifestations of those laws—cats playing with mice, and ichneumon larvae eating caterpillars—could not embody ethical messages, but he somehow hoped that unknown higher laws might exist “with the details, whether good or bad, left to the working out of what we may call chance.”
Since ichneumons are a detail, and since natural selection is a law regulating details, the answer to the ancient dilemma of why such cruelty (in our terms) exists in nature can only be that there isn’t any answer—and that framing the question “in our terms” is thoroughly inappropriate in a natural world neither made for us nor ruled by us. It just plain happens. It is a strategy that works for ichneumons and that natural selection has programmed into their behavioral repertoire. Caterpillars are not suffering to teach us something; they have simply been outmaneuvered, for now, in the evolutionary game. Perhaps they will evolve a set of adequate defenses sometime in the future, thus sealing the fate of ichneumons. And perhaps, indeed probably, they will not.
Another Huxley, Thomas’s grandson Julian, spoke for this position, using as an example—yes, you guessed it—the ubiquitous ichneumons:
Natural selection, in fact, though like the mills of God in grinding slowly and grinding small, has few other attributes that a civilized religion would call divine…. Its products are just as likely to be aesthetically, morally, or intellectually repulsive to us as they are to be attractive. We need only think of the ugliness of
or a bladder-worm, the stupidity of a rhinoceros or a stegosaur, the horror of a female mantis devouring its mate or a brood of ichneumon flies slowly eating out a caterpillar.
If nature is nonmoral, then evolution cannot teach any ethical theory at all. The assumption that it can has abetted a panoply of social evils that ideologues falsely read into nature from their beliefs—eugenics and (misnamed) social Darwinism prominently among them. Not only did Darwin eschew any attempt to discover an antireligious ethic in nature, he also expressly stated his personal bewilderment about such deep issues as the problem of evil. Just a few sentences after invoking the ichneumons, and in words that express both the modesty of this splendid man and the compatibility, through lack of contact, between science and true religion, Darwin wrote to Asa Gray,
I feel most deeply that the whole subject is too profound for the human intellect. A dog might as well speculate on the mind of Newton. Let each man hope and believe what he can.
Michele Aldrich sent an even better literary reference than any I had found. Mark Twain, in a biting bit of satire called “Little Bessie Would Assist Providence,” chronicles a conversation of mother and daughter—daughter insisting that a benevolent God would not have given her little friend “Billy Norris the typhus” and visited other unjust disasters upon decent people, mother assuring her that there must be a good reason for it all. Bessie’s last rejoinder, which summarily ends the essay as you shall see, invokes our old friends, the ichneumons:
Mr. Hollister says the wasps catch spiders and cram them down into their nests in the ground—alive, mama!—and there they live and suffer days and days and days, and the hungry little wasps chewing their legs and gnawing into their bellies all the time, to make them good and religious and praise God for His infinite mercies. I think Mr. Hollister is just lovely, and ever so kind; for when I asked him if he would treat a spider like that he said he hoped to be damned if he would; and then he—Dear mama, have you fainted!
James W. Tuttleton, chairman of the English department at New York University, sent me a stunning poem by Robert Frost that seems designed as a commentary upon Darwin’s last statement that chance may regulate in the small, even if purpose might be found in the large. Or do we even see true purpose in the large? The poem is called, simply, “Design”:
I found a dimpled spider, fat and white,
On a white heal-all, holding up a moth
Like a white piece of rigid satin cloth—
Assorted characters of death and blight
Mixed ready to begin the morning right,
Like the ingredients of a witches’ broth—
A snow-drop spider, a flower like a froth,
And dead wings carried like a paper kite.
What had that flower to do with being white,
The wayside blue and innocent heal-all?
What brought the kindred spider to that height,
Then steered the white moth thither in the night?
What but design of darkness to appall?—
If design govern in a thing so small.
I was so struck by the image of the spider as a drop, the flower as a froth, the moth as a pair of two-dimensional wings. Forms so unlike, yet all white and all brought together in one spot for destruction. Why? Or, as we read the last two lines, may we even ask such a question? I think that we cannot, and I regard this insight as the most liberating theme of Darwin’s revolution.
WHEN I FIRST WENT
to sea as a petrified urbanite who had never ridden anything larger than a row-boat, an old sailor (and Navy man) told me that I could chart my way through this
if I remembered but one simple rule for life and work aboard a ship: if it moves, salute it; if it doesn’t move, paint it.
If we analyze why such a statement counts as a joke (albeit a feeble one) in our culture, we must cite the incongruity of placing such a “mindless” model for making decisions inside a human skull. After all, the essence of human intelligence is creative flexibility, our skill in grasping new and complex contexts—in short, our ability to make (as we call them) judgments, rather than to act by the dictates of rigid, preset rules. We are, as Konrad Lorenz has stated, “specialists in nonspecialization.” We do not behave as machines with simple yes-no switches, invariably triggered by definite bits of information present in our immediate environments. Our enlightened sailor, no matter how successful at combating rust or avoiding the brig, is not following a human style of intelligence.
Yet this inflexible model does represent the style of intelligence followed with great success by most other animals. The decisions of animals are usually unambiguous yeses or noes triggered by definite signals, not subtle choices based upon the assessment of a complex gestalt.
Many birds, for example, do not recognize their own young and act instead by the rule: care for what is inside the nest; ignore what is outside. British ethologist W. H. Thorpe writes: “Most birds, while they may be very attentive to their young in the nest, are completely callous and unresponsive to those same young when, as a result of some accident, they are outside the nest or the immediate nest territory.”
This rule rarely poses evolutionary dilemmas for birds, since the objects in their nests are usually their own young (carrying their Darwinian heritage of shared genes). But this inflexible style of intelligence can be exploited and commandeered to a nefarious purpose by other species. Cuckoos, for example, lay their eggs in the nests of other birds. A cuckoo hatchling, usually larger and more vigorous than the rightful inhabitants, often expels its legitimate nest mates, which then die, frantically begging for food, while their parents follow the rule: ignore them for their inappropriate location, and feed the young cuckoo instead. We can intellectualize our anthropomorphism away, but we cannot expunge it from our aesthetic reactions. I must confess that no scene of organic activity makes me angrier about the world’s injustice than the sight of a foster parent, its own young killed by a cuckoo, solicitously feeding a begging parasite that may be up to five times its own size (cuckoos often choose much smaller birds as their hosts, and the fledglings may be much larger than their foster parents).
During a recent trip to the Galápagos Islands, I encountered another, interestingly different, example of birds that twist this common rule to different uses. This time, both the victim and benefactor are true siblings and the end result, although condemning weaker siblings to death, is evolutionary advantage for family lines.
The boobies (along with their cousins, the gannets) form a small (nine species) but widespread family of seabirds, the Sulidae. (Everything, and more, that you will ever want to know about sulids you will find in J. Bryan Nelson’s magnificent monograph:
The Sulidae: Gannets and Boobies
, 1978.) Earliest references in the Oxford English Dictionary indicate that boobies received their unflattering name, not for the distinctive waddling walk of one major display, big feet out and head held high in a behavior called “sky pointing,” but for their remarkable tameness, which allowed sailors (bent only on destruction) to catch them so easily.
A blue-footed booby incubates an egg inside the guano ring marking its “nest.” Galápagos, North Seymour Island.
PHOTO BY DUNCAN M. PORTER
Three species of sulids inhabit the Galápagos Islands: the red-footed, the blue-footed, and the masked booby. The red-footed booby lays a single egg in a conventional nest built near the tops and edges of trees and bushes. By contrast, its cousin of markedly different natural pedicure, the blue-footed booby, lays its eggs on the ground and builds no true nest at all. Instead, it delimits the nesting area in a remarkable and efficient way: it squirts guano (birdshit to nonornithologists who have not read
) in all directions around itself, thus producing a symmetrical white ring as a symbolic marker of its nest.
Within this ring, the female blue-foot lays, not one (as in many boobies), but from one to three eggs. In his most impressive discovery, Nelson has explained much about the breeding behavior and general ecology of boobies by linking the production of eggs and young to the quality and style of feeding in parents. Boobies that travel long distances (up to 300 miles) to locate scarce sources of food, tend to lay but a single large egg, hatching into a resilient chick that can survive long intervals between parental feedings. On the other hand, when food sources are rich, dependable, and near, more eggs are laid and more young reared. At the extreme of this tendency lies the Peruvian booby, with its clutch of two to four eggs (averaging three) and its ability to raise all chicks to adulthood. Peruvian boobies feed on the teeming anchovies of their local waters, fish that may be almost as densely packed in the ocean as in the sardine cans that may become their posthumous home.
The blue-foot lies between these two tendencies. It is a nearshore feeder, but its sources have neither the richness nor the predictability of swarming anchovies. Consequently, conditions vary drastically from generation to generation. The blue-foot has therefore evolved a flexible strategy based on the exploitation by older siblings of their parents’ intellectual style: yes-no decisions triggered by simple signals. In good times, parents may lay up to three eggs and successfully fledge all three chicks; in poor years, they may still lay two or three eggs and hatch all their chicks, but only one can survive. The death of nest (or, rather, ring) mates is not the haphazard result of a losing struggle to feed all chicks with insufficient food, but a highly systematic affair based on indirect murder by the oldest sibling.
I was reminded of the quip about painting and saluting while observing blue-footed boobies on Hood Island in the Galápagos. Their guano rings cover the volcanic surface in many places, often blocking the narrow paths that visitors must tread in these well protected islands. Parents sit on their eggs and young chicks, apparently oblivious to groups of visitors who gawk, gesticulate, and point cameras within inches of their territory. Yet I noticed, at first by accident, that any intrusion into a guano ring would alter the behavior of adult birds from blissful ignorance to directed aggression. A single toe across the ring elicited an immediate barrage of squawking, posturing, and pecking. A few casual experiments led me to the tentative conclusion that the boundary is an invisible circle right in the middle of the ring. I could cautiously advance my toe across the outer part of the ring with no effect; but as I moved it forward, as slowly and as unobtrusively as possible, I invariably passed a central point that brought on the pronounced parental reaction all at once.
Three hours later, I learned from our excellent guides and from Bryan Nelson’s popular book (
Galápagos: Islands of Birds
), how older siblings exploit this parental behavior. And, anthropomorphic as we all must be, it sent a shiver of wonder and disgust up my spine. (Science, to a large extent, consists of enhancing the first reaction and suppressing the second.) The female blue-foot lays her eggs several days apart, and they hatch in the same order. The firstborn sibling is thus larger and considerably stronger than its one or two ring mates. When food is abundant, parents feed all chicks adequately and the firstborn does not molest its younger siblings. But when food is scarce and only one chick can survive, the actions of younger sibs evoke (how, we do not know) a different behavior by big sister or brother. The oldest simply pushes its younger siblings outside the guano ring. As human mammals, our first reaction might be: so what? The younger sibs are not physically hurt and they end up but a few inches from the ring, where parents will surely notice their plaintive sounds and struggling motions and gather them quickly back.
But a parental booby does no such thing, for it operates like our proverbial sailor who made an either-or judgment by invoking the single criterion of movement. Parental boobies work by the rule: if a chick is inside the ring, care for it; if it is outside, ignore it. Even if the chick should flop, by happenstance, upon the ring, it will be rejected with all the vehemence applied to my transgressing toe.
We saw a chick on Hood Island struggling just a foot outside the ring in plain sight of the parent within, sitting (in an attitude that we tend to read as maternal affection) upon the triumphant older sibling (which did not, however, seem to be smirking). Every mother’s son and daughter among us longed to replace the small chick, but a belief in noninterference must be respected even when it hurts. For if we understand this system aright, such a slaughter of the innocents is a hecatomb for success of the lineages practicing it. Older chicks only expel their siblings when food cannot be secured to raise them all. A parental struggle to raise three on food for one would probably lead to the death of all.
The rule of “nurture within, ignore or reject outside” cannot represent all the complexity of social behavior in nesting boobies. After all, most birds are noted “egalitarians” in their division of labor between sexes, and male boobies are almost as attentive as females in incubating eggs and chicks. Since each brooding stint lasts about a day, boobies must permit their mates to transgress the sanctity of the guano ring when exchanging roles of care and provision. Still, the basic rule remains in force; it is not flouted but rather overridden by specific and recognized signals that act as a ticket of admission. K. E. L. Simmons, working on Ascension Island with the related brown booby, described the extensive series of calls and landing rituals that returning mates use to gain admission to their territory. But when adults trespass upon the unattended territory of an unrelated bird (as they often do to scrounge nest material on the cheap), they enter as “silently and as inconspicuously as possible.”
If chicks could perform the overriding behavior, they too could win readmission to the ring. Indeed, they learn these signals as they age, as well they must, for older chicks begin to wander from the ring as they gain sufficient mobility for such travels at about four to five weeks of age. (Nelson argues that they wander primairly to seek shade when both parents are foraging; overheating is a primary cause of death in booby chicks.) Yet hatchling boobies display only a few behaviors—little more than food begging and bill hiding (appeasement) gestures, as Nelson demonstrates—and the overriding signals for entrance into the ring are not among them.
The third species of the Galápagos, the white, or masked, booby, works on a more rigid system, but follows the same rules as its blue-footed cousin. Masked boobies are distant foragers, feeding primarily on flying fish. By Nelson’s maxim, they should be able to raise but one chick. Sometimes, masked boobies lay only one egg, but usually they provision each nesting site with two. In this case, “brood reduction” (to use the somewhat euphemistic jargon) is obligatory. The older chick always pushes its younger sibling outside the nest (or occasionally stomps it to death within). This system seems, at first, to make no sense. The blue-foots, whatever our negative, if inappropriate, emotional reactions, at least use sibling murder as a device to match the number of chicks to a fluctuating supply of available food.
By what perverse logic should masked boobies produce two eggs, yet never rear more than one chick invariably branded with the mark of Cain? Nelson argues forcefully that clutches of two eggs represent an adaptation for greatly increased success in raising
chick. The causes of death in eggs and young hatchlings are numerous—siblings intent upon murder being only one of many dangers to which booby flesh is heir. Eggs crack or roll from the nest; tiny hatchlings easily overheat. The second egg may represent insurance against death of the first chick. A healthy first chick cancels the policy directly, but the added investment may benefit parents as a hedge worth the expense of producing another egg (they will, after all, never need to expend much energy in feeding an unnecessary second chick). At Kure Atoll in the Hawaiian Archipelago, for example, clutches of two eggs successfully fledged one chick in 68 percent of nests examined during three years. But clutches of one egg fledged their single chick only 32 percent of the time.
Evolutionary biologists, by long training and ingrained habit, tend to discuss such phenomena as the siblicide of boobies in the language of adaptation: how does a behavior that seems, at first sight, harmful and irrational really represent an adaptation finely honed by natural selection for the benefit of struggling individuals? Indeed, I have (and somewhat uncharacteristically for me) used the conventional language in this essay, for Nelson’s work persuades me that siblicide is a Darwinian adaptation for maximizing the success of parents in rearing the largest number of chicks permitted by prevailing abundances of food.