How to Build a Dinosaur (23 page)

Creating a demonstration suitable for soundbite television is not, however a reason to do scientific experiments. In order to get to the point where the question—How did you do that?—could be answered, we would have to learn a great deal. And we would tie molecular biology to macroevolution. We would zero in on a significant passage in vertebrate evolution, the transition from nonavian dinosaurs to birds, and pin it down to molecular changes in embryonic cells.

The scientific significance of such a demonstration would be great. If we know the pattern of the release of growth and signaling factors, then we can read back to what genes are being turned on and off, and we can provide a flow chart for the growth of a dinosaur’s tail and the changes that make for the growth of a pygostyle. The science would not be in the showmanship of presenting a dinosaurlike chicken. The more characteristics like this we can pin down, the more detail we have on the small molecular changes that cause macroevolutionary changes in shape.

This is the heart of the promise of evolutionary developmental biology, to show how molecular changes effect large and obvious changes in animal shape of the sort that we have always tracked in paleontology. We can see dinosaurs appear in the fossil record, radiate into an astonishing variety of shapes and sizes and behaviors over 140 million years, and largely disappear, leaving one strain of descendants, the birds. Experimenting with embryonic development in an attempt to reverse evolutionary changes and bring back atavistic characteristics is the logical next step, the way to use the knowledge of evo-devo to test hypotheses in the lab. Call it
revo-devo
.

Basic research is at the heart of science. And I don’t want to underestimate the value of the search for knowledge for its own sake. Nobody goes into the study of dinosaurs whose primary goal is to seek breakthroughs in practical knowledge. Nonetheless, this is part of science, and society at large rightly asks what benefits will come from research. That is particularly important if public money is being spent on research, but it is also important if the kind of research makes some people uncomfortable, which is certainly the case when it comes to intervening in embryonic development, even of chickens.

Vertebrate paleontology may seem to be so remote from the daily problems of the modern world that it exists apart from society. It offers great entertainment and wonder—witness the popularity of museums’ dinosaur halls. But, if I were to be harsh, to ignore the unpredictable ways new knowledge of all sorts can add to our lives, I might ask, What good is it?

There is an aspect of vertebrate paleontology that is highly useful and of great importance to us as vertebrates. That vertebrate body plan that is so resilient, that has survived and prospered through flood, volcanoes, mountains rising and falling, and the bombardment of the earth by comets and asteroids, is one we share with dinosaurs, chickens, and countless other creatures. And the most basic aspects of how a vertebrate embryo grows are ones we have in common with all other vertebrates. So it should not be a surprise that there are paleontologists who teach anatomy in medical schools, or perhaps anatomists who also have a passion for fossils.

The result of this commonality of life, in this case in the specific fraternity of four-limbed vertebrates, is that lessons we learn about the growth of any tetrapod embryos may have significance for the growth of human embryos. Hans’s research on the tail, for instance, has led him to work on the spinal chord and notochord and to investigate how that growth can be disturbed or redirected. That can clearly be of use to medicine, since spinal cord defects are among the most common and devastating.

If we learn about the growth factors that signal the neural tube to continue developing, it’s possible that this knowledge could be useful in preventing birth defects. Humans do not have tails. But we do have spinal cords, and the growth and development of the two are intimately connected.

In spina bifida, for instance, incomplete development of the spinal cord can leave an infant with painful and sometimes lethal birth defects. In the 1980s researchers pinned down the importance of folic acid to the development of the spinal cord in human embryos. This discovery was made partly by gathering information about the diets of pregnant women and the incidence of spinal-cord birth defects like spina bifida, and partly with animal research. The simple remedy of adding folic acid to the diet of pregnant women now prevents countless cases of these defects. Hans is pursuing basic research on embryonic development, but at such a fundamental level that it is likely to have applications far beyond chickens and dinosaurs.

The chances for reasonable success in building a dinosaur are very good, and the benefits for basic and applied science that may accrue from the research, whatever the end result, are potentially very large. And here I should mention again that the end result, a dinosaur, is not really the goal of the research. It is a target, a means to an end. The ultimate goal, and the end toward which the research is aimed, is to increase our understanding of evolution and development and the connections between them. We learn as much from mistakes as we do from successes. So, for instance, Hans’s findings about the number of vertebrae in the chick tail as it begins to grow and the way in which the program of tail growth is disrupted and then redirected, are results well worth the work he has done. If he or someone else eventually manages to re-create a dinosaur, fantastic. If not, I am confident that what we learn along the way will be worth the effort.

Knowing that there are great potential benefits to be had in basic and applied science from trying to make a dinosaur, answers some significant questions about whether the research should be done. But there are other questions. Is it a morally justifiable act to play with life in order to go back in time? Is it cruel to the experimental subject? Is it dangerous to us or our environment?

I am not really going to answer all these questions, because morality and ethics are individual matters. I’m just not comfortable coming out with a statement that this or that practice is right, and the other is wrong. What I can do is to put the experiment I’m suggesting in the context of generally accepted scientific practice and common sense. I think that the experiment can advance science but that it does not really pose new ethical challenges. It is well within the kind of research now accepted in science. The deep into the waters of animal rights and the fundamental opposition to all experimentation on animals are subjects for another book, or several books.

Those are questions that apply to entire fields of science, to farming, to using animals for food, to keeping pets, to having zoos, to the ethics of farming, land use, population growth, to the question of what constitutes a person with legal rights and protections. They are worth discussing, but they are not questions I have answers to, or in which I have any particular expertise.

What I want to say is that the attempt to make a dinosaur as I’m suggesting fits within the common practices of science and medical research. On the big questions, it does not occupy such a special position that it needs to be discussed separately. It may seem extreme, but I don’t think it is.

First off, what Hans is doing so far, and the only work that he is planning, involves working with embryos, none of which will hatch. Experimentation on an embryo, at his university and most universities, does not come under the rules that govern the welfare of animals involved in experiments. There are those who object to any such experimentation regardless of how it is performed or what the benefits are, but that’s a bigger moral, philosophical discussion.

Experimentation of all sorts on chicken embryos is widely accepted and, I think, the correct assumption is that we are not causing the embryo pain. As to ultimately sacrificing the embryo, or a fully grown chicken, there are far greater injustices and indignities that billions of chickens face every day. Common sense would suggest that not allowing an egg to hatch, or humanely killing even a full-grown chicken, are actions that society recognizes as legitimate, given even the small return of a meal. The potential return is much greater here.

No one is ready to let an embryo experiment hatch yet. But when that point is reached, when the plan is to have a fully formed dinosaurlike chick hatch, then the experiment will come under review boards that deal with animal welfare. My sense is that providing a chicken with arms with claws instead of wings, with teeth, and with a tail, would not be cruel. In fact, if the atavistic structures grew improperly or were malformed in a way that would cause the animal pain, that in itself would mark a clear failure, since the whole point is to re-create functioning atavistic characteristics, not monstrosities.

There are research programs that do create monstrous animals of a sort. In order to understand human diseases, in particular the genetics of disease, many genetically altered mouse strains have been created by knocking out or inactivating a particular gene or set of genes. Some of these so-called knockout mice are obese, diabetic, hairless, or the mouse equivalent of schizophrenic. Others are prone to develop cancers or other inherited diseases. Clearly, and this is the case with other experiments as well, we are willing to cause suffering to these mice if it is a necessary part of a valid experiment.

Although there are plenty of examples of human beings acting cruelly, we also recognize cruelty when we see it, in a common-sense way. The committees that review animal experiments at universities have a variety of technical rules, but in essence they are designed to eliminate unnecessary pain, and to judge the value of an experiment if it will cause suffering to an animal. As a society we have, in the past, been willing to experiment even on close relatives, like chimpanzees, if the potential benefit were important enough, combating AIDS, for instance. That is changing now, but these are really decisions for the society at large. In the case of an adult chicken that had developed as a theropod dinosaur, the experiment would only be successful if the animal were comfortable and well-functioning.

That may not be so easy, because it may be necessary to make other changes in bone or muscle structure, or neck length, to allow a long tail to be functional. As for the claws and teeth, the chicken/dino would need to be able to use its forelimbs. They would have to have grown complete with proper nerve and muscle growth properly mapped to the controlling brain. The teeth would also have to be functional, and not interfere with the chicken’s diet. The red jungle fowl, the ancestor of all domestic chickens, which can still interbreed with domestic chickens, eats mostly insects, seeds, and invertebrates. Domestic chickens will eat almost anything including worms, salad, fruits, grains. As long as the teeth didn’t interfere with eating standard modern chicken feed, the creature would be okay. And that diet could be supplemented with other foods like worms and crickets, for which the teeth might be helpful.

There is a whole range of possible objections that have nothing to do with the health or life conditions of what we could probably call chickenosaurus. And that is fear for the environment, for interfering with the delicate ecological balance of the planet. Many people fear genetically modified crops, for instance, or genetically modified foods. It seems to me that the odds of harm occurring from eating genetically modified foods are very small. There is, of course, always a small chance that something new will cause an allergic reaction in some people. Other than that, the nutritional value of the corn or meat seems the same. Genetic modification also occurs in traditional selective breeding, or the kind of grafting and hybridization that goes on in developing new plant and seed varieties.

Selective breeding does not, of course, move genes from one species to another, and again there is some possibility for surprise. But I am getting away from chickenosaurus. If the embryo is not allowed to hatch, then it won’t be out in the environment at all. If it were allowed to hatch, and somehow escaped, the only problem would be the chickenosaur figuring out how to survive. It would not be a danger to the environment or to the billions of chickens in the world, because, as I’ve described, we would not be changing its genetic makeup. By manipulating growth signaling factors we would be switching genes on and off at different times during development, but not changing the genes themselves. Genetically, chickenosaurus would still be a domestic chicken. And if it were somehow to breed with a chicken, the result would only be more chickens.

Think of the difference in height between some immigrant groups and their children. Better nutrition during pregnancy and childhood leads to an increase in height. But there has been no genetic change. The growing child has simply had more fuel and, with the same genes as shorter parents, has grown taller.

A less happy but similarly instructive example could be babies born addicted to heroin or cocaine because of a mother’s habits. When the baby grows up there are no new addiction genes that it can pass on. So chickenosaurus would be harmless.

If our understanding of embryology and evolution reaches the point at which we know how to alter DNA to change the growth program, then we could make animals that would pass on their characteristics to their offspring. That will bring up another set of potential problems. It seems unlikely that chickenosaurs would take over an environment rife with raccoons, opossums, cats, dogs, coyotes, foxes, fishes, snakes, rats, and people. Still, altering the genes of an animal, as is done with knockout mice, is not something I am suggesting.

That would really produce the possibility of Jurassic Park, and attendant problems, although probably not vicious raptors rampaging through the kitchens of Southern California. More important would be the question of whether such animals would be functional in the outside world if they escaped. Even as an invasive species, they could disturb environmental equilibrium.