In June 1980, Luis and Walter Alvarez and their associates startled the scientific community by announcing that dinosaurs had not died out be-cause of gradually changing environmental conditions 50 million years ago. Instead, they said, mass extinctions took place when an extraterrestrial body slammed into the Earth, throwing a pall of dust and ash over the planet that lasted for years. Initially skeptical, paleontologist David M. Raup helped analyze data on marine fossil extinction that changed his mind, eventually arguing for a 26 million-year cycle of extinctions that probably were tied to solar system or galactic forces. Others continued to refine the theory, postulating the return every 26 million years of Nemesis, the hypothetical small companion star of our Sun that sends comets from the Sun's Oort cloud hurtling toward our planet, altering its ecology. Raup's new book "The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science" (W W Norton & Co., 1986) is an insider's account of the development of the theory and its reception by scientists, the media and the public. But the book also examines how scientists' belief systems impair their ability to evaluate and test new ideas dispassionately. The following is adapted from the Raup book.
The structure of science, with its rigid procedures and standards for testing of hypotheses, helps to organize our knowledge (and ignorance), and the results of the "scientific method" are probably more objective and dispassionate than in most other fields of human inquiry. But the process still con-tains strong emotional and sociological elements. Almost all scientists think they know how science differs from philosophy, religion and plain guesswork. Most will argue that religion is not science because religion involves no experiments, tests no hypotheses, and is committed beforehand to a set of beliefs. Science and faith are antithetical. It follows that scientific research is objective because the scientist is not influenced by prior expectations and is willing to let the chips fall where they may. I think these statements contain a fair amount of bunk.
All sciences work within theoretical frameworks, called models, paradigms, hypotheses, concepts, principles or precepts. In nearly all cases, the theoretical frameworks are "thought up" by imaginative scientists. They usually start out as little more than hunches-perhaps suggested by observational data but not required by them. The periodic table of the elements was not forced on chemistry by an immense weight of evidence that allowed no other interpretation.
Once a new theory or paradigm is pro-posed, it is tested and evaluated by the scientific community-assuming it is reasonably credible and evokes enough interest. New or old observations or experiments are evaluated in light of the new idea. If they fit, the new idea is supported. If they don't fit, the new idea gets a black mark. Rarely is there a single crucial experiment to prove or disprove the new idea.
All this is straightforward and has its counterparts throughout human affairs. But there is a tricky aspect. The new idea is a! most never in a vacuum: one or more other ways of describing or explaining the same phenomena already exist and are accepted by the scientific community. Walk up to an astronomer and ask: How was the universe formed and how old is it? You will always get an answer, regardless of the decade or cen tury in which you ask the question. Yet the answers change as new ways of interpreting the observations become established.
Acceptance of any new theoretical framework depends on credibility and improvement on existing alternatives. In cases where the choice is not immediately obvious, the burden of proof generally lies with the new idea. Given a choice, the scientific community invariably sticks with the conventional wisdom. Furthermore, the older ideas have usually been around long enough to have accumulated supporting evidence, whereas the new idea rarely has much going
for it, at least at first. It is not a fair game.
Despite the lack of "fairness" to new ideas, the traditional practice in science may serve us better than a more democratic mode. History shows that most new ideas fall. Science would be very confused much of the time if all new ideas were given precisely equal treatment. It is clear that the new theory is guilty until proved innocent, and the pre-existing theory is innocent until proved guilty.
Although I am somewhat uncomfortable with this procedure, it is a strong element in the culture of science and may even move us ahead in the long run. But it has a some-times crippling effect on progress, especially if the conventional wisdom in a field has been established for a long time with its innocence supported by a great variety of evidence. The persistence of the Ptolemaic system of astronomy is a classic example. It was accepted by virtually all educated people,
partly because of inertia and partly because it worked remarkably well as a predictor of eclipses and so forth. Its replacement by the Copernican system was a long and difficult process.
Perhaps the only thing that saves science from invalid conventional wisdom that be-comes effectively permanent is the presence of mavericks in every generation-people who keep challenging convention and thinking up new ideas for the sheer hell of it or from an innate contrariness.
One should not discuss the subject of belief systems in science without mentioning Alfred Wegener's theories of continental drift. The strong conventional wisdom of the time was that continents and ocean ha-sins are permanent, fixed. Today, this is all changed. We now have drifting continents as part of the larger paradigm of plate tectonics. This paradigm shift has been hailed a major revolution in the history of science. Comparing the continental-drift literature with that of the Nemesis Affair, one can see a similarity in tone and method of argument. Continental drift was guilty until proved innocent.
My question is: To what extent have the events making up the Nemesis Affair been influenced by preconceived belief systems? Have the scientists who study Nemesis been influenced by their own biases? so, is the effect important or trivial?
The Nemesis Affair shows many examples of the conflict between new and old the-ones. But it is virtually impossible to prove the guilty-until-proved-innocent bias. When an article contains a list of 10 reasons why the Cretaceous-Tertiary extinctions could not have been caused by impact, there is no way to know to what extent the author is consciously or unconsciously selecting or slanting the data. With regard to the original Alvarez proposal of the Cretaceous-Tertiary impact, I am reasonably sure that protection of the conventional wisdom has played an enormous role.
What will happen if Nemesis and the related theories turn out to be wrong? There will be some red faces, of course, and some gleeful ones as well. But by and large, the scientific community will absorb the event. No careers will be ruined and no staff will be reprimanded. In fact, some of the more active participants may receive some professional rewards for having shown the imagination necessary to think up new ideas and stimulate research in new areas.
The story is not yet over. Nemesis has not been found and much controversy rages over whether there is even any need for Nemesis. That is, the claim of periodicity in extinction on which Nemesis is based is still being debated and new lines of evidence are being sought. I suspect that the day will come, perhaps rather soon, when we will look back on this period and wonder how we ever thought the Earth could have been unaffected by all those things whirling around above our heads.
Science is an extremely pluralistic endeavor, and the culture varies somewhat from discipline to discipline. But I don't think there are many fundamental differences in the way science is done. All fields have strong conventional paradigms that are constantly under fire. Some of the paradigms are well founded in observation and experiment; others are simply logical con-structions that "seem" to work. And every so often, there is a revolution whereby the old paradigm is replaced by a new one. It is a wonderful area of scholarship to be in-so long as you do not take the wisdom of the moment too seriously.
Raup is Sewell L. Avery Distinguished
Service Professor of Geophysical Sciences at the University of Chicago, 60637.
Copyright © 1986 by David M. Raup. Reprinted with the permission of the publisher, W. W. Norton & Company, Inc.