Homo sapiens. Translation: knowing man. A creature that lives up to its name, and then some. Though physically indistinguishable from its immediate forebears—the late Pleistocene hominids that appeared about forty thousand years ago—Homo sapiens has grown clever enough to reconstruct the lives of creatures that went extinct ages ago, then to develop fictional accounts of those lives in the form of books and movies. And science and art are but two of its many notable creations. Consider agriculture, religion, language, custom and ritual, social, legal, and political institutions, economic systems, technologies, cities, the Brooklyn Dodgers, any of the aspects of contemporary existence that can be considered expressions and elaborations of culture. If Homo sapiens hadn't had a large brain it wouldn't have developed culture, and if it hadn't developed culture it wouldn't now call itself human. Knowing man became modern man by means of acculturation.
Some students of natural history have said that with the emergence of culture, evolution ceased for Homo sapiens. A buffer now exists between the selective pressures of the physical environment and the reproductive fortunes of the individual, making us less dependent for our survival on characters modified through descent than on technologies, institutions, and the like, none of which are inherited, in the strict biological sense of that term. But I think this outlook misses the point. First and foremost, and I can't say this often enough, the law of life is change through time. It's the one process we hold in common with every other organism on Earth, including the dinosaurs. Natural history is our history as well. It's where we came from; it's what made us; it's who we are. As I said earlier, any family album is a record of this fact, of change through time, evolution. What's missing from the family album are indications of the forces driving change. To capture that you have to see how human beings interact with their environment.
In doing so it will be helpful to keep in mind that evolutionary change almost always starts as a minor modification of behavior. One of the current inhabitants of one of the Galapagos Islands is an iguana that lives near the shore and feeds on algae. Evidently its kind was pushed from the interior of the island to the less populous perimeter, where it now spends a large part of its life in the water, though lacking most of the physical features possessed by other, more familiar forms of aquatic life—whales, say, or fish. In the animal called marine iguana, in short, morphology has not yet caught up with behavior. How might the two eventually converge? Any slight physical variation that confers on an individual iguana an adaptive advantage in an aquatic environment—an increase in the webbing between the toes, for instance—may increase the probability that that individual will survive and successfully reproduce, passing the trait along to the next generation.
The more general observation one can make about the marine iguana is that organisms are not always perfectly matched to their environments. This is why I part company with those who say, "The natural world is so orderly, so well designed. How could it have happened by chance?" My response to this assertion is that if nature were not well designed, how would we know? Where might we find the ideal design by which we could judge whether the world as it exists today is perfect? I believe instead that if you look closely at natural history, at the lives of particular organisms, you see that evolution isn't following a plan. Certainly it's constrained by lim-its—the law of gravity, for instance—but within those boundaries it does nothing but conduct experiments, small-scale, extremely slow experiments in which contingency plays a major role and the price of failure or bad luck or simple exhaustion is extinction. The truly remarkable feature of this experimentation is that, given a sufficient amount of time and a certain series of interactions between organisms and their environments, novel morphological characters and, eventually, entire new organisms emerge. And, just as important, the novelties are adaptive, they work, they persist—in the case of dinosaurs, for tens of millions of years.
Among human beings the equivalent of the marine iguana's eating habits is the staggering array of activities that fall under the heading culture. These changes, remember, despite having already transformed the face of the planet, occurred largely within the last twelve thousand years, which, from an evolutionary standpoint, is a very short period of time, too short, certainly, for morphology to have caught up with behavior. Even so, some minor effects can be seen—the apparent increase in people with poor vision, for example. With the invention of eyeglasses, individuals who would have had difficulty performing any of a thousand occupations—from hunting woolly mammoths to operating an unwieldy computer— have no trouble whatsoever, thereby increasing the likelihood that what was once a life-threatening handicap, now rendered harmless, will be inherited and thus more widely distributed.
The most pressing question, as I see it, isn't whether Homo sapiens is still evolving but instead whether the latest innovations in the hominid line—big brain, consciousness, culture—will truly prove adaptive in the long run, irrespective of any additional physical changes that might in time emerge. We know that these innovations aren't necessary for survival. Cockroaches seem to get along just fine without them. And nothing matches the evolutionary resilience of the lowly group of organisms that includes bacteria and algae. They have been around since the early days of life on Earth, and seem capable of surviving just about any environmental disturbance short of the complete destruction of the biosphere. Where, then, are all of our newly acquired human traits taking us? What are the advantages of moving in that direction? The disadvantages? What does it say about our chances for survival to be the only creature on Earth capable of posing these questions? Does it say anything? Could it be that consciousness is nothing more than a cruel hoax, rendering us the first organisms to foresee our own end, to bear witness to our own destruction?
Somber questions, yes, and all the more so for being unanswerable. Time will tell. Meanwhile, let's pretend that we know more than we do and speculate a bit about the phenomenon of consciousness. One thing is certain: It didn't arise fully developed or come from nowhere in particular. Everything in nature is the result of incremental modification, which means that every apparent radical transformation was preceded by a very long series of very small changes, which means in turn that many of the attributes we associate with consciousness aren't entirely unique to us. There are overlaps. We have many relatives in the animal world, and under certain circumstances some of them honor us with unforgettable lessons in relatedness.
I recall talking to a keeper at the Wild Animal Park outside San Diego about a certain female chimpanzee who always sat by herself, apart from the other animals, an outcast. So disliked was she that the dominant male attacked her often, and viciously, seemingly without provocation. Why, I asked, was that particular adult female being persecuted? Several years before, it seems, she had lived at the San Diego Zoo, where, for some reason, she mistreated another adult female and her young, one of which was a singularly robust male. When that male grew up, he assumed control of the pack and when the pack was transferred to the Wild Animal Park, where environmental conditions were less domestic, he reverted to typical chimpanzee behavior, taking revenge upon the tormentor of his youth. In other words, he remembered the actions of the older female from years past and he punished her for it, not once, but repeatedly. Although more difficult to document, chimpanzees may plan ahead as well, though in a very primitive way—the unforgiving male laying in wait for the beleaguered female, for instance. That suggests some degree of foresight.
In human beings, by comparison, both of these capabilities have undergone an enormous amount of refinement. Take our obsession with looking into the future. We didn't stop at planning for tomorrow. We started wondering about the day after tomorrow, then the one after that, reaching ever further ahead, and that made us anxious. Not long afterward we discovered a Supreme Being who offered assurance that our future is in good hands. Now, there are lots of ways to talk about the relationship human beings have formed with supposed higher orders of existence, but the word most commonly used in such discussions is soul, an innermost self that stands apart from everything else as a distinct entity. Soul is a word that rarely surfaces in scientific discussions, and that's understandable, but I think there's a way to think about it that reconciles the interests of science and religion, at least tentatively.
Ask yourself this question: Of all of the attributes that distinguish human beings—the nickname we have given to ourselves— from Homo sapiens, what's the most definitive, the one without which all the others would not exist? Surely it's that point in the development of consciousness when the idea of the soul was born. You could say that the creation of human beings began with the inception of the soul, and therefore that that event separates us from other organisms, because this particular character is unique to us. Human beings came into existence the moment Homo sapiens began worrying about the distant future and formed a relationship with a Supreme Being in whose hands it entrusted its fate. If you were in a Linnaean frame of mind, you might say further that at that juncture in evolution a new type of biological creature emerged. In other words, human beings may not be the pinnacle of primate existence but instead the most primitive version of what's to come. I'm not asking you to believe this. Just play with it, as a way of thinking about the future of mankind and the dilemmas we face. Whatever conclusion you may come to about the soul, it's an idea that's had a profound impact on human history, and for that reason alone it cannot be ignored.
Another dimension of sapient existence you might want to consider is specialization and its implications for survival. The first human beings to arrive in North America, like the first organisms in any new habitat space, were generalists, capable of performing any of a wide range of occupations that might be required to stay alive under an equally wide range of environmental circumstances. They secured and prepared food, built shelter, made clothes, tended to illness and injury, domesticated animals. If no one person possessed all of these skills, the skills were nonetheless well represented in the small bands and tribes in which the people lived. But as time went by and civilizations developed, and especially since the Industrial Revolution, the environment became partitioned into increasingly smaller and more diversified niches. One can now survive as a paleontologist, for instance, without knowing how to grow corn or rice, dig a well, weave a sweater, or do much of anything else, because there are legions of specialists who themselves do nothing but farm, build and repair things, sew, take out the garbage. In midtown Manhattan, until very recently, there was a shopkeeper whose sole occupation was repairing zippers. For more than fifty years that's all he did, and there was enough call for his highly specialized craft that he made a good living at it.
Such situations are commonplace in large cities, because that's where specialism is most extreme and, as everyone knows, humanity seems hell-bent on urbanization, gathering together in increasingly larger collectives that now number in the millions, even, in a few cases, in the tens of millions. From one perspective, places like New York City and Mexico City and New Delhi can be seen as monuments to the ingenuity of human beings, their seemingly limitless capacity for innovation. From another perspective, it all seems rather precarious. Think of the high susceptibility of low-latitude organisms, the overwhelming plenitude of insects in the Amazon rain forest, for instance. Such richness of biological expression is surely one of the marvels of the natural world. But that marvel is sustained at some risk. All that's needed to destroy it is a small environmental disturbance. Though the parallel is far from exact, the marvelous diversity of modern civilization also comes with an inherent liability. Should the world's industrial economies collapse all at once, say, in response to a global decline in fuel production, cities will be especially vulnerable. Far removed from sources of food and other basic requirements, and lacking a workable range of practical skills, urban residents will be thrown into chaos. Homo sapiens would probably survive such a global catastrophe, but there may come a time when human beings would not, and the process of civilization would have to begin anew.
Without going into the history of religion and law, it also seems clear that when the soul came into being, whether as a concept or something more substantial, a moral dimension was added to human existence, and nowhere are the complications of consciousness more evident than in moral debates about the issue of extinction, not our own but that of other organisms with which we share the planet. Nature, as I argued earlier, is not following or fulfilling a plan. There's no master blueprint for evolution that would give us the grounds to say, "Well, the loss of that species was a big mistake." There are patterns in nature but no mistakes, no right or wrong direction, no preordained destinations from which we might be deterred. Most of life seems to understand this, more accurately, not to give it any thought. No one cried over the demise of the dinosaurs. If that event were to occur today, however, tears surely would fall. Human tears. Because, unlike nature as a whole, we make plans. We make judgments about deviations from our plans. And we know what no other creature knows—that sometimes we are to blame for the deaths of others.
I don't see any way out of this dilemma. We'll probably argue over our impact on other species and what to do about it for the rest of our days on Earth. And we'll be unable to free ourselves of the paradox of settling disagreements about the best interests of the natural world in thoroughly man-made settings—Congress, the federal courts, and so on. But meanwhile I think we should get used to the idea that the organisms that can put up with us—deer, coyotes, possums, cockroaches—are the most likely to endure, regardless of the heroic efforts we may make on behalf of others. I'm not saying that such efforts are necessarily misguided or doomed to failure, only that the overall trends of human history, increased industrialization and urbanization, coupled with continued population growth, show no sign of slowing down. This is placing a tremendous amount of environmental stress upon other plants and animals, which in turn is selecting for characters compatible with the rising tide of civilization, a process not unlike the flooding of the continents during the Cretaceous period. The difference, of course, and it's all the difference in the world, is that inland seas are without consciousness and thus untroubled by a sense of responsibility. That, it seems, is a burden we alone carry. In exchange for memory and foresight we gave up our innocence. An old story, surely, retold here in somewhat different terms. According to the evolutionary version, however, there's no going back, no way to restore the world to a previous state. Time travels in one direction. And the only escape from time is death.
Does the foregoing seem a little far afield for a dinosaur paleontologist? It doesn't to me. In one sense or another I have wandered all of my life, when not actually walking through barren hills and rocky washes in search of fossils, then letting my imagination run free. Even if this or that particular expedition fails to turn up anything of value the exercise alone keeps one limber, in body and mind, and alive to fresh possibilities, without which existence would be a pretty joyless affair. Besides, generating ideas is a different activity from testing them against the evidence, and every idea, regardless of origin, should be put to the test. That's the credo of scientists, at any rate.
In practice the second part of this process is more dynamic than it might sound. For one thing, the evidence in paleontology is always changing—expanding, being refined, sometimes undergoing complete reinterpretation. An idea that once seemed to contradict the available data is resurrected when it's learned that the data was skewed. For another, our means for collecting evidence also changes, creating new avenues of research, provoking altogether novel ideas. The heroic version of science would have us believe that it progresses under the force of brilliant, probing minds boldly interrogating the mysteries of the universe—in short, by means of direct confrontations between human beings and nature, consciousness trained like a laser on this or that puzzle. And surely there's some truth to this. But just as often, advances in scientific understanding follow advances in the tools and procedures of inquiry. Astronomy and molecular biology provide the most obvious examples. Imagine the status of these fields today if the telescope and microscope, to say nothing of the more sophisticated devices that succeeded them, had never been invented.
A similar claim might one day be made about paleontology. Using CT scans, computerized imaging programs, microscopy, and other advanced methods, we are starting to extract heretofore unheard-of kinds of information from fossils. An entire vista of discovery, micropaleontology, has opened up in recent years. Although this technological revolution is in its infancy—the most useful benefits so far coming from histologic studies like those I described in chapter 8—it's already showing great promise, convincing me that the bones paleontologists and others have been collecting for the past 150 years have a great many more stories to tell about the lives of dinosaurs. All we need do is learn how to listen. And that's precisely what we're attempting at our laboratory at the Museum of the Rockies, where the new techniques are being tested on real-world problems. Here are three recent projects:
Kristi Curry, now a graduate student at the State University of
New York, Stony Brook, has prepared histologic profiles ofjuvenile apatosaur forelimbs found at Mother's Day Site, comparing them with similar bones recovered from an excavation in Colorado. Her primary aim is to gain insight into sauropod growth. From the standpoint of physiology, the sauropods are the most baffling of all of the dinosaurs. They were the largest known land animals, weighing up to fifty tons, yet their heads were tiny, their mouths even more so. To get an idea of the proportions—rather, disproportions—picture your head reduced to the size of a peanut. How they managed to eat enough to survive from one day to the next is a mystery. But they did more than that. One of the most successful four-legged creatures ever, the sauropods lived for more than 100 million years. So far, Kristi has found densities of vascularization and tissue patterns consistent with cows and other ungulates, suggesting that apatosaurs grew rapidly until they were half grown, or about thirty feet long. But she has also turned up evidence of variation in growth rate in different bones of the same animal, which tells us that temperature regulation in dinosaurs may be even more complicated than we had thought.
In another effort to make fossils speak in new ways, postgraduate student Mary Schweitzer has been trying to extract DNA from the bones of T. rex. Originally, like Kristi, she had intended to thin-section the bones and conduct a histologic investigation. But under the microscope there appeared to be blood cells preserved within the bone tissue. Mary conducted a number of tests in an attempt to rule out the possibility that what she'd discovered were in fact blood cells. The tests instead confirmed her initial interpretation. Then, using certain chemical processes, she tried to isolate the cells. That didn't work. So next she tried, with some success, to recover proteins, including DNA and collagen, the chief constituent of skin, ligament, and bone. DNA, of course, could help determine hereditary relatedness. Complete sequences of numerous animals would be required, however, so that goal is a long way off. Collagen, too, varies from one individual to the next and thus could be used as a kind of chemical fingerprint. Regarding either prospect, however, the work Mary is doing represents one of the first small steps in what may prove to be a tremendously fruitful area of laboratory research.
My final example involves computer graphics. You'll recall that to be able to conduct our recent histologic studies of baby hypacrosaur and maiasaur bones, my wife, Celeste, and I first had to simulate near-term embryonic skeletons and position them within reproductions of their eggs, so as to determine how large the hatchlings were at birth—in other words, to make sure that the bones we were analyzing actually belonged to babies. The software for developing and manipulating three-dimensional figures has been around for some time now, and we've been experimenting with other applications. But we have also begun to explore the uses of so-called morphing programs, the most promising of which enables us to visualize how a particular dinosaur grew from infancy to adulthood.
One of the reasons this has proved helpful is that dinosaurs didn't mature linearly; the adult skull, for example, isn't merely a blown-up version of a juvenile one. Like the skulls of birds and mammals but unlike those of reptiles, the skulls of dinosaurs changed shape during development. In general they start out with long foreheads and big eyes and end up with sloping foreheads and eyes that are proportionately smaller. Imagine how odd it would be if a robin chick or a lion cub retained its baby features throughout life. Indeed, it's the peculiarity of that fictional condition, and our reflexive response to it, that explains the universal appeal of such figures as Mickey Mouse and items like teddy bears. I'll come back to this very shortly.
In our collection at the museum we now have hypacrosaur skeletons representing five different stages of growth. We made drawings of the fossils, and entered the two-dimensional images into the computer. The morphing program then averaged the five pictures and filled in the intervals between each one, giving us a continuous depiction of dinosaur growth—a little movie, so to speak. Unlike Jurassic Park or The Lost World, however, our film repre-
Skulls of Hypacrosaurus stebingeri showing its nonlinear growth. The 50 percent morph is a linear result of morphing the nestling with the adult. The half-grown juvenile shows the actual configuration of the skull. Note that the snout hasn't elongated, and the nasal crest hasn't developed. The half-grown Hypacrosaurus retains its juvenile characteristics.
sents a digitized version of the real thing—skeletons. It is the best approximation yet of someone actually having been present with a camera in a hypacrosaur rookery 74 million years ago. Watching the transformation that occurs during development is an unforgettable experience. (The hypacrosaur on the book jacket is represented at about the age when it would have started to assume more adult characteristics.) As the skull matures the snout grows longer and flattens out, like a duck's bill. The eyes recede and become less prominent. Along the forehead the crest expands upward, eventually forming, in the case of the adult male, a high, narrow ridge, a sort of bony crown turned upright, in the shape of a very exaggerated mohawk.
This merely hints at what we hope to accomplish in the coming years. As we perfect the morphing software, expanding to three-
dimensional programs and increasing the overall resolution of the imagery, we will assemble a library of growth series, which can then be used as a basis for identifying bones (those of different baby duckbills are especially difficult to tell apart), constructing simulations of stages for which we have no representative fossil remains, hunting for evidence of telling anatomical structures (maybe nasal turbinates turn up only at certain stages of development in certain dinosaurs), and in general exploring the relationship between developmental morphology and other aspects of dinosaur life. In the case of Hypacrosaurus, it seems likely that one of the reasons the young did not possess full-size crests is that it would have disrupted the social hierarchy and communication processes within the herd. The crest was one of the male adult's display features, for intimidating rivals and attracting mates. But it was hollow as well, and connected to the nasal passages, which means that it was probably used to trumpet sounds during courtship, when danger loomed, and so on. Having heedless juveniles in the herd that were capable of making these sounds would only have confused matters.
Judging from the growth of the skull, in particular, Hypacrosaurus also appears to have taken full advantage of a survival strategy that's common in warm-blooded animals—the retention of baby features. Hypacrosaur young kept their youthful appearance until they were about half grown, after the point when, according to our estimates, they were capable of leaving the nesting grounds. A number of studies with human children have shown that the longer one retains baby characteristics, the longer one will be cared for. Such features trigger instinctual parenting responses, even in other children, which probably explains why when a child brings home a stray, more often than not it's a puppy or a kitten, not an adult animal. More generally, if you happened to be a baby that could not care for itself, it would be to your advantage to have a face that melts the hearts of grown-ups. Which is exactly the scenario I see for Hypacrosaurus, Maiasaura, the Milk River lambeosaur, and many other dinosaurs. What purpose would it serve to retain baby features if from the moment you were hatched the herd treated you like an adult?
With our arrival at the first, experimental morphing images we've completed a circle. We started by discussing the role imagination plays in our attempts, both scientific and not-so-scientific, to reconstruct the lives of dinosaurs. We then traveled into the field to collect more fossils and more information, subjecting our finds to further study in the laboratory, extracting secrets from bones that only a short while ago we would not have imagined they possessed. The guiding ambition behind all of the work we've done since leaving Egg Mountain was to create a fuller, more forceful vision of the dinosaurs, only this time as characters in an epic drama, an evolutionary saga that spans millions of years. In all instances, though, the interplay between fact and imagination never ceased.
With dinosaurs, it can never be otherwise. The stories will always be incomplete, ambiguous, under revision, and we'll always want to fill in the missing pieces. Because we can't help it. Seeing what's not really there—remembering and anticipating—is one of the things we do best. We are, I think, a perfect match, Homo sapiens and Dinosauria. Knowing man meets the partially known but unmistakably real, a factual footing for an ever-restless imagination. Wherever fate leads us, then, doubtless we'll continue to turn around now and again, glancing backward, taking the measure of who we are against everything that ever was. And once upon a time the dinosaur was. It actually was. That's where we began. It's where we'll begin again.
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