Eight Little Piggies (29 page)

Richard Leakey almost surely has many square miles of good sediment from this crucial time in his field area at West Turkana. But he is not yet searching these beds. He is concentrating his efforts on older rocks of the early Miocene (15 to 20 million years ago) when the bush of apes had its great initial flowering in Africa. He is working before the time of maximal intrigue for several reasons. In part, he may be saving the best for later, perfecting his techniques and “feel” for the region before zeroing in on the potential prize. He also has the fine intuition and horse sense of any good historian—it may be best to begin at the beginning and work forward. But, most importantly, he has a professional’s understanding that problems of maximal public acclaim are not always the issues of greatest scientific importance.

The public may yearn, above all, to know the status of our common ancestor with chimpanzees, but Richard Leakey recognizes that the early Miocene is also a time of mystery, promise, and conceptual importance: mystery because we know so little about the actual diversity of apes at this time of their greatest success; promise because he has sediments that can deliver many of the missing goods; conceptual importance because we have as much to learn from documenting the base of our ancestral bush as in searching for the little branchlet that led directly to us later on. The early Miocene is a good place to explore.

The ground of West Turkana glistens with crystals of quartz and calcite. The local Turkana children, passing time during long hours of tending goats under the relentless sun, collect geodes into piles and smash them to reveal the crystals inside. We are looking for duller fragments of bone.

There are no great secrets to success, no unusual basis for “Leakey’s luck,” beyond hard work and experience. In some areas, fossil-bearing strata are rare and must be traced through geological complexities of folding and faulting to assure that fieldworkers search only in profitable places. But here, the entire sequence is fair game (although some strata, as always, are richer than others), and all exposures of rock must be scrutinized. The key to success becomes patience and a trained workforce.

Leakey maintains a staff of trained Kenyan observers. He provides a long course in practical mammalian osteology (study of bones)—until they can distinguish the major groups of mammals from small scraps. The main ingredient of Leakey’s luck is unleashing these people in the right place.

Kamoya Kimeu supervises this exploration. He has found more important fossils than any one else now alive. One night in camp, he told me his story. As a boy, he tended goats, sheep, and cattle for his father. He attended school for six years and then went to work for a farmer. His employer urged him to return to school and study to become a veterinary paramedic. Kamoya then walked for several days back to Nairobi, where his uncle told him that Louis Leakey, Richard’s father, was recruiting people to “dig bones.” His mother gave him only cautious approval, telling him to quit and come home if the task involved (as he then suspected) digging up human graves. But when he saw so many bones from so many kinds of creatures, he knew that nature had strewn these burial grounds. The sediments of West Turkana are, if anything, even more profuse.

When I arrived on January 16, Kamoya’s team had just found a new and remarkably well-preserved ape skull (in a profession that usually works with fragments, mostly teeth, a skull more than half complete, and with a fully preserved dentition, is cause for rejoicing). The next day, we studied and mapped the geological context and then brought the specimen back to camp. I wrote in my field book: “Everyone is very excited because they have just found the finest Miocene ape skull known from Africa. It is quite new—with a long face, inflated nasal region, incisors worn flat with a diastema [gap] a finger wide to the massive canine—almost like a beaver among apes.”

The greatest of all fossil finders Kamoya Kimeu gathering material at West Turkana.
Photograph by Delta Willis
.

Research is a collectivity, and we all have our special skills. Kamoya’s workers are the world’s greatest spotters; Richard also has a hawk’s eye, the intuition of a geologist who has lived with his land, and the organizational skills of a Washington kingpin; his wife, Meave, has an uncanny spatial sense and can beat any jigsaw champ in putting fossil fragments together; yours truly, I fear, is good for one thing only—seeing snails.

All field naturalists know and respect the phenomenon of “search image”—the best proof that observation is an interaction of mind and nature, not a fully objective and reproducible mapping of outside upon inside, done in the same way by all careful and competent people. In short, you see what you are trained to view—and observation of different sorts of objects often requires a conscious shift of focus, not a total and indiscriminate expansion in the hopes of seeing everything. The world is too crowded with wonders for simultaneous perception of all; we learn our fruitful selectivities.

I couldn’t see bone fragments worth a damn—and Richard had to direct my gaze before I could even distinguish the skull from surrounding lumps of sediment. But could I ever see snails, the subject of my own field research—and no one else had ever found a single snail at that site. So I rest content with my minuscule contribution, made in character, to the collective effort. At the top right of page 143 in the November 13, 1986, issue of
Nature
—the article that describes the new skull—a few snails are included in the faunal list of the site, some added by my search image. (I also found, I believe, the first snails at the important South African hominid site of Makapansgat in 1984—where I also couldn’t see a bone. I think I am destined to be known in the circle of hominid exploration as “he who only sees the twisted one.”)

The traditions of nature writing demand that this personal narrative now continue at some length, with overwritten paeans to the wonder of this discovery, set in glowing clichés about the stark and fragile (two good adjectives) beauty of the countryside. But I desist. First of all, this isn’t my style; it also doesn’t match anything that actually happens in the field. People have varied reactions to such good fortune. Some may jump up and down, fall upon their knees to praise God, or wax eloquent about the new line wrested from nature’s complex book. Most people I know, certainly including Richard, Kamoya, and myself as outsider, do not have personalities that match these romantic stereotypes. The conversation may flow more happily at dinner; some kind of glow must form within. But you still have to make sure that the trucks have gas, that the water jugs are full—and you do have to get up at dawn the next day because it’s too hot to work in the afternoon. My favorite kind of excitement is quiet satisfaction.

Richard and Kamoya’s team found a second, smaller ape skull that field season at West Turkana. Both are new genera, not merely variants on familiar themes of the ape’s bush. Richard and Meave Leakey published two papers in the November 13, 1986, issue of
Nature
describing these new forms as
Afropithecus
(the one I witnessed) and
Turkanapithecus
. In the most interesting line of the
Afropithecus
paper, they write: “
Afropithecus
displays characters typical of a variety of Miocene hominoids combined in a single taxon.” In other words, this new genus represents a unique combination of features known to vary among early apes—as if we might shuffle the known variations into many more plausible combinations as yet undiscovered. The bottom line after all this exegesis is simplicity itself: We are not at, perhaps not even near, the asymptote for true diversity of apes at their flourishing beginning. If one field season in uncharted lands could yield two new genera, how many remain undiscovered in the hundreds of square miles still open for exploration? Apes were bushier than we had ever imagined during their early days; human evolution seems even more twiggy, more contingent on the fortunes of history (not enjoined like the successive rungs of a ladder), less ordained, and more fragile. Our vaunted march to progress, the standard iconography of our evolution, is just one more expression of life’s little joke.

I have consciously permitted a professional’s bias to permeate this essay so far. I have been equating “success” with numbers of branches on the bush—for paleontologists tend to view large-scale evolution as the differential birth and death of species, and we slip too easily into an equation of success with exuberance of branching. But, of course, we must also consider the quality of twigs, not merely their number.
Homo sapiens
is one small twig, holding with just a few others all the heritage of a group once far more diverse in branches. Yet our twig, for better or for worse, has developed the most extraordinary new quality in all the history of multicellular life since the Cambrian explosion. We have invented consciousness with all its sequelae from Hamlet to Hiroshima. Life’s little joke shows us our fragility, our smallness on the proper metaphor of the bush, but we have turned the joke upon itself with the power of one evolutionary invention.

The prophet Micah caught both sides of this tension with great understanding when he wrote that fragility and size of origin imply little about ultimate effect: “But thou, Bethlehem Ephrathah, though thou be little among the thousands of Judah, yet out of thee shall he come forth unto me that is to be ruler in Israel” (Micah 5:2). If we could merge the two themes, and if rulers could learn humility and respect from our common origins as fragile twigs on the bush of life, then we might break the equation between ability and right to dominate and might even fulfill that most famous of Biblical prophecies, which is, after all, about the proper nurturing of trees and bushes—“and they shall beat their swords into plowshares, and their spears into pruning hooks.”

CHARLES DARWIN
was a master of metaphor, and much of his success may be attributed to his uncanny feel for timely comparisons that virtually compel understanding. We all know the two metaphors that Darwin invoked to define his theory: natural selection and the struggle for existence. We might also consider Darwin’s three principal descriptions of nature, each wonderfully apt and poetic, and each a metaphor.

The tangled bank:
To stress the intricacy of relationships among organisms as arising, somewhat paradoxically, by planless evolution. Darwin begins the last paragraph of the
Origin of Species:

The tree of life:
Borrowed from other contexts to be sure (Proverbs 3:18, for example), but used brilliantly by Darwin to express the other form of interconnectedness—genealogical rather than ecological—and to illustrate both success and failure in the history of life. Darwin placed this famous passage at a crucial spot in his text—the very end of chapter four, marking the conclusion of his argument for natural selection (the rest of the book discusses problems and examples):

The face of nature (and the darkness behind):
To argue that apparent balance and harmony arise from the struggle and death of individuals:

But if Darwin relied on metaphors to enlighten his readers, he also followed this good strategy in his private quest for understanding. Darwin’s notebooks are, if anything, more awash in metaphor than his published works. I believe, along with many Darwin scholars (see, in particular, Ralph Colp’s 1979 article in bibliography), that one metaphor stands out among all others in Darwin’s own struggle to formulate the principles of natural selection—the metaphor of the wedge. At the very least, this comparison holds pride of place as the first image invoked by Darwin to explicate his initial statement of natural selection.

Great ideas, like species, do not have “eureka” moments of sudden formulation in all their subtle complexity; rather, they ooze into existence along tortuous paths lined with blind alleys (to invoke a metaphor). Still, not all moments are equal, and some may even be judged crucial. Darwin, at least, claimed that September 28, 1838, had been the key day for natural selection, and that his reading of Thomas Malthus’s
Essay on the Principles of Population
had enabled him to put the disparate pieces of his puzzle together, as he recalled Malthus’s argument that growth in population, if unchecked, must quickly outstrip food supply, leading to inevitable struggle for limited resources and death for losers. He wrote Malthus’s principle into his notebook and appended, directly thereafter, his very first metaphor for his new theory of evolution:

Darwin honed and sharpened this metaphor throughout the next twenty years, as he prepared for the storm of publishing his ideas about evolution. He eventually settled upon the image of a surface absolutely chock-full with wedges, representing species in an economy of nature sporting a No Vacancy sign. Evolutionary change can only occur when one species manages to insinuate itself into this fullness by driving (wedging) another species out. Darwin developed this metaphor most fully in his manuscript for the long, unpublished version of the
Origin of Species
(a compressed account appears on page 67 of the shorter book that he eventually produced in 1859 under the pressure of A. R. Wallace’s independent formulation of natural selection):

I have focused upon Darwin’s commitment to the metaphor of the wedge because this unappreciated core belief, more than the notion of natural selection itself, shaped Darwin’s conventional view about progress and predictability in the long-term history of life. Darwin, like any honest man in a world of such inordinate complexity, struggled hard but failed to resolve several crucial issues in the interpretation of nature. No question troubled him more than the common assumption, so crucial to Victorian Britain at the height of industrial and imperial success, that progress must mark the pathways of evolutionary change.

Darwin clearly understood that the basic mechanics of natural selection implied no statement about progress, for the theory only speaks of local adaptation to changing environments. But Darwin, as an eminent, if critical, Victorian himself, could not let go of progress so cleanly. He wished to validate predictable advance as a major theme of the fossil record, but knew that the bare bones of natural selection could not rationalize such a belief. How, then, could progress be affirmed as a fact of life’s history if the fundamental theorem of organic change—natural selection—did not imply progress by itself?

To resolve this troubling discordance between the mechanics of his basic theory and his fundamental impression of pattern in life’s history, Darwin called upon a second, basically ecological principle encompassed by the metaphor of the wedge. Nature, Darwin believed, is full of species (“a surface covered with ten thousand sharp wedges…all packed closely together”). All potential addresses are occupied, but new challengers continually arrive to compete for space. They can succeed in a full world only by driving other species out in overt competition for limited resources (“the one driven deeply in forcing out others”). It’s a tough, crowded world out there; successful creatures claw their way to the top and remain there by constant vigilance and conquest. The
Origin of Species
contains several passages about progress in the history of life, and all are validated, not by the bare bones mechanism of natural selection, but by the second principle of the wedge, the vision of a full world ruled by overt competition among organisms:

But what actual evidence do we have that long-term trends in the history of life arise by continuous and intense biological competition in a perennially crowded world? (Other models for the operation of natural selection are surely plausible. Perhaps most species do not fall victim to overt wedging by superior competitors but to changes in the physical environment that are too rapid or extensive to elicit an adaptive response.) I am persuaded that some cases in Darwin’s preferred mode of organic competition have been documented. Biologist Geerat Vermcij (who lays out the brief for Darwin’s view most elegantly in his book
Evolution and Escalation
), for example, has demonstrated a geological trend for thicker and stronger crab claws matched by ever more efficient defenses (spines, knobs, and thick shells) in the snails that crabs love to eat. I accept the interpretation of this lock-step escalation as an “arms race.”

But just as we needed so great a scholar as Aristotle, in so weighty a place as the
Nicomachean Ethics
, to teach us that one swallow does not make a spring (yes, he said spring, not summer), a case or two in the fossil record does not establish a pattern. Directional trends produced by wedging do occur, but they scarcely cry for recognition from every quarry and hillslope. The overwhelming majority of paleontological trends tell no obvious story of conquest in competition. Why did the large and gorgeously complex ammonites crash to oblivion some 65 million years ago, while their rarer and apparently simpler closest cousins, the nautiloids, survived to our own day as the “ship of pearl” immortalized by Oliver Wendell Holmes (and Eugene O’Neill) as the builder of “more stately mansions.” Why did all members of three great groups of crinoids die 225 million years ago, leaving all subsequent time to a fourth group that survives today but sports no feature ever identified as an improvement over the three losers? Why did a similar replacement of one group by another occur in reef-building corals at the same time, and why can no theme of improvement in competition be discerned here either? Why, for that matter, did dinosaurs die and mammals prevail after 100 million years of reptilian success and mammalian marginality? (If mammals were competitively superior, they certainly displayed no hurry in wedging out their “predecessors in the race for life,” for 100 million years is almost two-thirds of mammalian history. Moreover, recent views on the sleekness and anatomical sufficiency of dinosaurs speak strongly against any notion of wedging by rat-sized mammals.)

I chose these four cases for two reasons. First, I think that they are far more characteristic of the fossil record—more numerous and more significant in import—than putative examples of progress by wedging. Second, they represent the kind of event that most directly challenges the metaphor of the wedge and therefore the favored rationale for progress by rigorous competition among organisms—“changing of the guard” across episodes of mass extinction. In fact, these four cases provide a small sample of events, a pair for each, in the two most celebrated mass extinctions: the Permian debacle that may have wiped out more than 95 percent of marine invertebrate species some 225 million years ago, and the Cretaceous event that removed remaining dinosaurs and gave mammals a chance some 65 million years ago.

Any reader with a good feel for the history of paleontology must now be intensely puzzled. How can I be suggesting that a study of mass extinction will alter our view about directionality in the history of life when widespread and coincident death of species is, perhaps, our oldest discovery about the stratigraphic record? The boundaries of the geological time scale, the alphabet of my profession, are defined by events of mass extinction. The two episodes cited in my cases separate the three great eras of life’s multicellular history: the Permian extinction between the Paleozoic and the Mesozoic, and the Cretaceous extinction between the Mesozoic and the Cenozoic. How can something so canonical, and so long appreciated, now threaten to disrupt another cherished view about biologically based competition leading to progress in a crowded world?

A resolution to this historical puzzle calls upon a conventional interpretation of mass extinction that makes peace with, or even supports, the notion of biotic struggle as the driving vector of life. Mass extinction is a specter haunting the metaphor of the wedge, but the ghostbusters of denial and accommodation have held the fort—until recently. Darwin himself chose the more vigorous response of denial, trying his darndest to dissolve mass extinction (or at least to dilute it to insipidity) with his favorite argument about “the imperfection of the geological record.” A hopelessly inadequate record can compress millions of years of missing data into an apparent “event.” If we could recover the full flow of time, the individual items of a “mass extinction” would spread out on both sides of illusory suddenness, indicating a much longer period of successive disappearances at a rate little, if at all, accelerated beyond the usual tempo of wedging in ordinary times.

A more popular argument (the ghostbuster of accommodation) admits the unusual character of mass extinctions, acknowledging a substantial acceleration in the tempo of death, while arguing that the environmental stresses of these parlous times do not introduce a new regime in the causality of dying, but rather, only accentuate the power of the wedge. In these worst of times, the motor of biological competition runs faster as increased stress drives up the intensity of struggle. Mass extinction only “turns up the gain” on business as usual. If the “ancient and beaten” make their exit in ordinary times as superior wedges push themselves into the bustling economy of nature, then the rate of departure can only accelerate in the tough moments of mass extinction when dogs eat dogs and men must be men.

This honing of the wedge provides the traditional context, usually not well explained in general writing on mass extinction, that has made all the recent news about truly catastrophic causes based on extraterrestrial impact so controversial and so threatening. In 1980, the father and son, physicist and geologist team of Luis and Walter Alvarez, along with Frank Asaro and Helen Michel, first published their evidence that a large extraterrestrial object struck the earth some 65 million years ago and triggered the great Cretaceous extinction.