How to Build a Dinosaur (22 page)

If we learn enough, this will give us enormous insight into the fundamentals of biology, development, and evolution. It will also be the first step in growing a dinosaur.

EXPERIMENTING WITH EXTINCTION

Way over 90 percent of all the species that have ever lived on this planet—ever lived—are gone. They’re extinct. We didn’t kill them all. They just disappeared. That’s what nature does. They disappear these days at the rate of twenty-five a day. And I mean regardless of our behavior. Irrespective of how we act on this planet, twenty-five species that are here today will be gone tomorrow. Let them go gracefully. Leave nature alone.

—George Carlin

 

 

I
hope that by now I have convinced you that we can start with a chicken embryo and hatch out something that looks like a nonavian dinosaur. Will it really be an extinct animal brought back to life? Would a tail, claws, and teeth be enough to say that we have brought such an animal back from extinction?

No. We would have brought back some of the characteristics of the dinosaurs. We would have used the signatures left by evolution in the chicken’s DNA to rewind evolution. But we would have re-created ancestral traits, not the ancestor itself. We could never truly re-create a species or genus that was lost, unless we had a complete genome. If we reached that point, then there would be philosophical disputes about whether we could really bring back an animal from deep time. There would always be gaps in our knowledge and, not ever having seen the animal, we could not be absolutely sure. But we would have brought back an animal that, by all our tests, was identical to the extinct animal.

This seems unlikely for animals from deep time, for practical reasons in retrieving a full picture of an ancient animal’s genome, as well as other influences on its development. But the more we pursue creating experimental atavisms, the closer we will come to this achievement, and the more we will learn about evolution, which is the deeper goal. The fundamental reason for attempting to rewind evolution is to learn how evolution occurs. Like a teenager with an old car, you take it apart to learn how it works.

On a shorter time scale we could certainly come close enough to re-creating an actual extinct species, but the achievement could well be an empty one. Let’s use the ivory-billed woodpecker as an example. This was the largest woodpecker in the United States and Canada and it is generally thought to have gone extinct perhaps half a century ago, although there have been many claims of sightings, including one that was published in
Science
on June 3, 2005.

Earlier that spring, when the announcement of the sighting was made and the paper on the woodpecker released to the press, I was planning this book with my coauthor, Jim Gorman, and he was called away in the middle of our conversations to fly to Alabama and write about the woodpecker. Since then, the sighting reported in the
Science
paper has been roundly criticized as a sighting of a pileated woodpecker, and no hard evidence in the form of a clear photo or video, or DNA, has emerged to prove the ivory bill’s continued existence.

There are woodpeckers that are in the same genus as the ivory bill,
Campephilus,
such as the Magellanic woodpecker from South America,
Campephilus magellanicus
. The Magellanic woodpecker is not descended from the ivory bill, but they share a recent common ancestor, recent in evolutionary terms. It seems possible that if we carefully documented the embryonic development of
Campephilus,
we might discover a way to make a
magellanicus
embryo develop to be indistinguishable from an ivory bill.

Whether we would want to is another question. I don’t know what there is to be learned in this case, since the differences are subtle, and the re-created ivory bill would not breed true. We could also sequence the genome of the ivory bill from skins saved in museums and compare it to
magellanicus
and find differences in the genome. If we found obvious differences, we could perhaps change the genome.

But even if we were able to create a bird that was indistinguishable from the old ivory bill, it would always seem ersatz, particularly since the dream of finding the ivory bill still living is about proving to ourselves that we were able to stop ourselves from driving a beautiful species into extinction. And for science and conservation and our own sense of the planet, the issue is not so much the bird itself but the bottomland hardwood forests it lived in. Without them, re-creating the bird would be like re-creating tigers without a jungle.

Other experiments might also be undertaken with a good chance of success. We could probably make the embryo of a domestic chicken grow into
Gallus gallus,
the wild chicken that is its ancestor. And if wolves disappeared we would have a great reservoir of genes in the domestic dog. Dealing with mammalian embryos is, however, quite difficult. Still, we have the dog genome, we can get the wolf genome now, while they are still living.

These would be very, very small triumphs of reverse engineering. Even to an untrained eye a Siberian husky and a wolf are not so far apart in appearance and behavior. We would be reversing microevolutionary changes. An untrained eye might not see the difference in the first place between one woodpecker and another. And behavior would be hard to re-create since it would depend, no doubt, on environment as well as genetic heritage.

 

In contrast to those experiments, however, the one that I am proposing—or campaigning for, I suppose you would say—promises significant benefits both in terms of basic research and applications. Turning the clock back from chickens to dinosaurs would open up to us a method to tackle the major changes of macroevolution and help us tie them to changes in the control of genes. And what we find out about intervening in embryonic development, particularly involving the growth of the spinal cord, could prove of great practical, medical use.

In the attempt to re-create a dinosaur, we can’t pick a species. That’s too fine a target. In another way that distance and time are connected, the farther away a target is at a shooting range, the larger the area you need to aim for. The farther back in time you go, the larger the target you might be able to hit. Research would have to aim at something phylogenetically larger, perhaps at the level of genus, or family. The farther we go back in time the less information we have about the extinct animals. Once we are in deep time, we are dealing with animals that we have imagined based on limited information. In some cases species have been named on the basis of a tooth, or not much more. Even with a relatively complete skeleton, there are so many areas where we would have to guess. Wait, let me rephrase that. We would have to hypothesize, based on the evolutionary context of the animal and other information. The color of the skin? The way the animal moved? Evidence based hypotheses, otherwise known as educated guesses.

What we can aim at with some certainty are the characteristics that we know from fossils—size and skeletal structure, teeth, musculature, and in some cases skin. We can make reasonable conclusions about movement and diet, and good guesses on certain aspects of behavior. For some behaviors, however, we would need herds of dinosaurs, complete with the appropriate predators and environment, to observe them. In other words—Jurassic Park. That is not something I will see in my lifetime. And probably not something worth pursuing.

How much we will eventually be able to achieve is impossible to say. We can keep pushing the boundaries of knowledge and ability, which will continue to grow. But the scientific capability must be balanced against mundane questions of money and usefulness and profound issues of ethics and social responsibility.

I have no doubt that we can and will do what I’ve proposed, to bring back teeth, tail, and forearms with claws. It won’t be easy and the money may not be forthcoming, but it will happen, and I’m convinced that it will be worth doing. I also think we could change the kind of feathers a chicken grows to make them more primitive. I think we could achieve a suite of changes in one embryo so that the resulting animal could hatch and live out a normal life span, eating, moving, and functioning without difficulty.

Beyond that, we’ll have to wait and see. As embryologists work out the details of the program for tetrapod development, I would expect many barriers to reengineering extinct life-forms to fall. Right now, we could change limb growth with many small interventions—adding and suppressing growth factors in different locations at different times. We may, however, find higher-level signals that lead to a cascade of developmental changes so that instructions for forelimb growth, for example, do not have to be adjusted piecemeal. There may be fewer changes needed than we now imagine to prompt development of a hand rather than a wing.

We may never know the physiology of long extinct animals. We can intuit certain internal arrangements from living birds, but I doubt that we will ever know exactly what the inside of
T. rex
looked like. Still, the more we try to rewind and replay the tape of evolution, the more we will learn about how animals are put together, how they grow. And we have clues in the digestive systems, to take one example, of modern birds with different diets. Combining the variations found in living birds and what we can learn of the diets of extinct animals, we may refine our ideas about the digestion of an extinct animal. If
T. rex
was a scavenger, for instance, we might look to see how modern avian scavengers cope with their diet.

None of these potential increases in our ability to reverse evolution, to be more confident of the accuracy of our ventures in developmental time travel, answer the political and moral question of whether this is the sort of thing we should do. To consider this question, or set of questions, we must think about benefits and risks, and about what the challenges might be to the ethics of such an experiment.

Among the potential benefits of causing a chicken embryo to develop dinosaurian characteristics is that this is a project that could capture the popular imagination. It could be a demonstration of evolution that would be felt at gut level by non-scientists who might be uninterested in the details of genomes and embryos.

Anything that brings home to the public the reality of evolution, and its place as the foundation idea of modern biology, is important. Anything that dispels the fog of confusion about science and religion would be enormously positive. I teach a course at Montana State University called “Origins.” This is not a paleontology class for students who are specializing in studying some form of evolution. This class is taught by a theologian and a cosmologist as well.

We have students planning a career in science. We have those who are not. Some students don’t express religious views, others make clear they are Christians, but not biblical literalists. Sometimes we have had young earth creationists. My approach to teaching the course is the same as my approach to teaching science in general.

I am not teaching or promoting or asking anyone to memorize and spit back at me the accepted understanding of evolution. What I am hoping for, always, is to get across the idea that science is a way of thinking that has no necessary conflict with religious or spiritual thinking.

The difference between science and religion or philosophy is sometimes said to be the kind of question asked. It’s more useful, I think, to look at the kind of answers that are proposed to any given question. In science you come up with an answer that can be proven wrong—a falsifiable hypothesis. Why does a stone thrown into the air fall to the ground? is a question to which there is an answer—many answers, actually. The testable answers, the ones that can be proven wrong, are scientific ones. If you propose a physical force called gravity that works in a certain way, that’s an answer that can be tested.

If I proposed that all things are drawn to the earth, that might seem a pretty good explanation until we started thinking about the moon and the sun and the stars and why they weren’t falling to the earth. In any case, it’s an answer that can be proven wrong, or incomplete. If I say that the stone falls because its spirit wishes to return to its home, that’s a spiritual answer. I can’t think of a way to test that to falsify it. So that answer is outside the realm of science. Theologians and philosophers may have a way to address it, but I don’t.

One of the benefits of actually hatching a dino-chicken would be that it would be shockingly vivid evidence of the reality of evolution—not a thought experiment but an Oprahready show-and-tell exhibit. The creature would be its own sound- and vision-bite. It certainly wouldn’t convince anybody who didn’t want to be convinced. But it would cause discussion and thought. What I like about the idea of using a chicken that developed into a dinosaur as evidence of the reality of evolution is that it is more than an idea. It is an experimental result. And it calls out for questions. What is it? How did you do it? Is it a circus freak or a trick? What does it mean? Without staking out a position or starting a war of words, the animal would prompt a discussion that would have to end up with the mechanisms of evolution and its footprint in the genes of living animals. Even more than a fossil, it would cry out for explanation.