that stones are intelligent as we understand intelligence, still less that stones are self-aware as we experience selfawareness. Let me try to explain what they mean. A former professor of physiology at Harvard Medical School, Walter Cannon-whom I remember as a very wise person-wrote a book called The Wisdom of the Body. What did he talk about in that book? Well, he talked about the very fine regulation of the concentration of glucose in the blood, of body temperature, of the pH of body fluids, and so on. As the great physiologist Claude Bernard said, the constancy of the internal environment is the condition of a free life. We can go to the Arctic or the tropics, and we are free because of all that internal regulation. But please note that the regulation is unconscious. It has nothing to do with will or intelligence. In fact, one can only interfere with the regulation by intruding with one's intelligence. The English scientist Galton tried for one day not to draw a breath without willing it. At some point he decided he'd had enough of the willing and then was deeply embarrassed to find that his breathing stopped. If he hadn't somehow gotten through that phase, he would have probably passed out, and the unconscious regulation would have taken over again.

Now in exactly the sense that one can speak of the wisdom of the body, one can speak of the wisdom of the planet, of the solar system, of the universe. But it is wisdom, not intelligence, and wisdom in the sense of fitting together. I may have seemed yesterday to be disparaging silicon when I said, "And that's why silicon is good for making rocks, but to make living organisms, we need carbon." But if silicon weren't good for making rocks, we wouldn't be here. Rocks are the skeletons of the planets-so thank heavens for rocks. Things fit to a remarkable degree.

Mind or consciousness are involved

George Wald

in a tremendous range of human activities. At one end is the child learning to avoid the fire. An awful lot of learning is just personal housekeeping. At the other end is mathematics. Tell me where mathematics comes from and wherein lies the rightness of mathematical thinking. One might think first of its self-consistency, but Gödel poked holes in that. I lived next door to a mathematician for a while-and I mean a creative mathematician, one who makes mathematics, not just uses it-and I never saw that man working. He spent his mornings in the bathtub and his afternoons quietly walking up and down the street with his little children. But he was a fine mathematician. Eugene Wigner wrote a nice essay asking how it is that mathematics fits physics so well. He concludes that it is simply a miracle, one for which we should be grateful.

I want to mention what Schrödinger, no mean physicist, says in the last chapter of his book What Is Life?. He says that he has been interested in Eastern philosophy for many years, and then he asks whether we are perhaps mistaken in thinking that there are as many minds as there are bodies. Clearly there

are many bodies, but perhaps there are many fewer minds, perhaps only one.

I do not believe in ESP, but I do think that the experiments done to determine whether ESP exists are laughable. They are like trying to produce a physical explanation for the existence of God. But the idea of one mind has something in

it.

Let me say one more thing. The Judeo-Christian god made the universe; the Hindu supreme god Brahman thinks the universe. Is it possible to think reality? Theoretical physicists seem to do it. It started when Paul Dirac saw that his wave equation for the electron was satisfied by another particle of opposite electric charge, and then that particlethe positron-was discovered the next year. Now it is pretty much taken for granted that if a theory describing some known aspect of reality has alternative solutions, those solutions also have physical reality.

Hubel: I would like to respond to the original question. We humans tend to make up words that have perfectly good uses the word sky is a good exampleand then try to reify those words, to identify them with physical things. The mind can no more be regarded as a thing located some particular place than the sky can. But astronomers don't study "the sky" or "the heavens" or worry about where "the sky" is. They study all that we know constitutes "the sky". Some day we may regard the mind and consciousness the same way.

My hang-up with what George talked about yesterday has to do with what makes biology profoundly different from physics and the other natural sciences, namely evolution. In terms of evolution, the mechanisms responsible for Cannon's wisdom of the body are very well understood right down to the molecular level. We have no indication that any such guiding force exists in, say, physics. I'm thankful that ice floats and that carbon atoms form

chains, and no one can say what a universe in which those facts didn't hold would be like. But I don't go along with invoking an all-permeating mind or consciousness to explain them. The very idea of a permeating force is a religious concept. It falls outside the realm of science. We have come a long way, thanks to scientists like Darwin, toward transcending the conflicts between science and religion. It is true that some scientists-Sherrington, Penfield, Eccles, and Schrödinger, for example-commit one part of their consciousness to science and hold in reserve some marginal part that is the source of soft statements. I find those statements disturbing because they tend to become identified as scientific statements although they are not. I'm not suggesting we should ignore everything outside science. I don't think that highly of science. But it's a good game to be in. It's very interesting, so interesting that I find talk about ESP rather silly. There are enough things to say gee whiz about in real science that we don't need silly things like astrology to keep ourselves happy. Audience: In the mid thirties von Neumann suggested that consciousness might play a very significant role in the interpretation of quantum theory, in the understanding of what measurement means. That idea was followed up by London and Bauer and is being pursued to this day by Eugene Wigner. It may be at the roots of one of the great physical theories of our time. I would like Professor Wald to comment on what he feels the role of consciousness might be in future theories of matter. Wald: First I want to respond to what David said. I am a scientist, and very glad to be one. In fact, I have spent my life pretty much as a strict constructionist in science. I certainly think that evolution is a great thing and that the wisdom of the body is understood. Perhaps natural selection was involved in the evolution of a universe in which ice

floats and carbon atoms form chains. Also I believe that every thoughtful scientist realizes that science deals only with a marginal part of reality. Reality is the very big picture, and science can deal cleanly and quantitatively with

only a portion of that reality. Science cannot deal with what are in many ways the most important aspects of our lives. A Harvard great, the mathematician George Birkhoff-do you know what a Harvard great is? A Harvard professor who is still there so he can tell you he is great-wrote a book called Aesthetic Measure. In it he presented a formula by which one could quantitatively assess the aesthetic value of a work of art, such as Beethoven's Ninth Symphony or Rembrandt's Self-Portrait. Then he decided to write a sonnet that would rate 100, and he did. It was a lousy sonnet. That is what the computer might dowrite lousy sonnets.

Hubel: George, I think you are misconstruing what I said. I would be the first to agree that science plays a marginal role in our lives and has little if any immediate relationship to the most important things we do and say. I was expressing a negative opinion about scientists who include, as a last chapter

in a supposedly scientific work, their wooly, nonscientific, difficult to understand thoughts about, say, mind and consciousness.

Wald: I don't share your negative feelings. Science is a path, one among many. It is the path to the boundaries of what we know. Of the many paths I prefer that of science to all others, perhaps because it does have boundaries. You seem to be saying that scientists shouldn't look beyond the boundaries, and if they do they should keep their wooly thoughts to themselves. Many scientists have looked beyond the boundaries-Newton, Maxwell, and so on down the line. How does one have the temerity to speak with superiority of such people? I'll admit, though, that we played that game as graduate students, saying too bad about that last chapter of Jeans', too bad about that last chapter of Eddington's.

Bitensky: It's time to move the discussion forward. I believe that David was not telling scientists to stay within the boundaries. He was saying that what lies beyond is simply not science. Now I would like Jack Sepkoski to comment

on how human consciousness might affect the speciation and extinction that characterize evolution on the earth. Sepkoski: First I want to emphasize that my comments yesterday about the constructive aspects of extinctionconstructive, that is, on a time scale of several tens of millions of years-were not meant to lend support to a so-what attitude toward the effects of human activities on the biosphere. After all, we have no way of knowing whether those effects will, in the long term, be constructive or destructive, and what may be constructive to the entire system in the long term may be very destructive to individual species, even ourselves, in the short term. But it is fairly clear that massive re-engineering of the earth is causing a departure from Darwinian evolution, and genetic engineering can only bring about an even greater depar

ture.

I should like to comment that I am less amazed by the existence of life than Professor Wald is, perhaps because of the rashness of my relative youth. Also I don't view intelligence as the pinnacle of creation, as being pre-eminent in and of itself. Intelligence is only one solution to survival, one that has been tried by a variety of organisms. Some organisms, the social insects, for example, rely on collective rather than individual intelligence. But survival of a species can be promoted by any number of tricks-by being camouflaged or showy, by being able to run fast, to reproduce quickly, to climb trees. That is why we enjoy such a rich variety of fauna and flora. But human intelligence coupled with culture is a factor very different in kind from those at work in evolution until the last few centuries, and the biosphere faces a whole new ball game. Before evolution had no purpose; it produced what could survive, not what should survive. Now the biosphere is increasingly subject to human purposes, to the uses we make of the

earth. Thus, the history of the earth, which extends back some four and a half billion years, has moved into a very different era.

Audience: May I ask Dr. Drake what will be the next step after signals from an extraterrestrial civilization are detected?

Drake: That will depend on what we detect. What is most likely to be detected is a signal at a signal-to-noise level so low that no information can be extracted from the signal. So we will know only that another civilization exists. But of course that will be big news in itself. Then we must do whatever is required-build a much larger radiotelescope system, for example-to obtain information about that civilization. That information may have a great influence upon our own civilization. Or it may turn out that the extraterrestrials are so different from us that learning about them will be motivated only by scientific curiosity, like learning about the ecology of elephant seals.

Audience: Dr. Sepkoski, you implied yesterday that some maximum number of species exists at any given time. What might be the mechanisms for enforcing that maximum?

Sepkoski: The maximum is a relative, not an absolute, maximum. Probably

some absolute maximum exists, since the earth can support only so much biomass and the efficiency of energy transfer can be only so great. But the number of species existing at any time has never been anywhere near the limit imposed by those factors. On the earth today we see local ecological systems, particularly islands, approaching an approximate equilibrium as new species appear and existing species vanish. The equilibrium number of species can increase or decrease, however, if a pool of species is introduced that uses the habitat and its resources in an entirely different way. That has been observed, for example, on oceanic islands and in a number of habitat islands on the continents. The fossil record over hundreds of millions of years for, say, the whole oceanic ecosystem presents a very similar picture. We see an approximately constant number of families and genera. We also see the equilibrium perturbed by several large mass extinctions and then quick rebounds to the former level. That level seems to be maintained by background extinction, or slow attrition, of existing species and slow replacement by other species. The slow attrition of species was probably caused by competition among organisms for limited resources as well as by perurbations or small "catastrophes" in local ecological communities; replacement resulted from normal processes of speciation. We also see jumps in the steady-state number of taxa when a different style of fauna appears, for example, when Ordovician fauna replaced Cambrian fauna. And the animals that became dominant after the great Permian extinction did things in yet a different way. So it makes sense that the number of species in the oceans today is greater than it was 250 million years ago. We can imagine that if marine organisms found yet another way of organizing ecosystems, their number might jump even higher. We see terrestrial paral

lels, especially among plants-plateaus of diversity maintained by balanced speciation and extinction and jumps in diversity due to new ways of doing things, particularly at the advent of angiosperms. We have some hints of the same thing going on with vertebrates and perhaps with insects, but the insect fossil record is pretty messy.

Audience: I'd like Dr. Sepkoski to comment on Fred Hoyle's theory that life at some level pervades the universe and that that cosmic life is the origin of life on the earth.

Sepkoski: I haven't thought very critically about Hoyle's version of panspermia because I find it too easy to dismiss out of hand. Many ideas of that sort are based on the notions that 4.5 billion years is not enough time to produce the diversity of life we see on the earth today or that 1 billion years-the time between the birth of the earth and the age of the earliest fossil evidence of life-is not sufficient time to produce life itself. Unfortunately, we don't have theoretical principles of evolution with which we can quantitatively predict absolute rates of evolution. All we have right now is an ability to measure relative rates of evolution in some situations. My impression from looking at the fossil record, though, is that evolution can work extraordinarily fast when it is unconstrained. In the absence of competition and crowding, mutations and other accidents produce a huge array of variations from which natural selection can

produce a wonderful array of outcomes. I don't believe we need panspermia or any other means of inoculating the earth with life. But that's only my gut reaction to what I see in the fossil record, and we do need quantitative theories before we can say definitively that such hypotheses are unnecessary. Bitensky: When we speak about evolution, we are really talking about the evolution of DNA, and there is now a lot of evidence that the shuffling of whole exons is one of the changes that occur in DNA. That shuffling allows the mixing of very big pieces of DNA and so could be responsible for very rapid evolution.

Sepkoski: Exon shuffling certainly leads to rapid rates of change in DNA, but in fact speciation doesn't require any changes in DNA. The extraordinary genetic variations among individuals of a species is more than sufficient. Mutation could cease today, and after tens of hundreds of millions of years a far different biota would inhabit the earth. Bitensky: But the extraordinary variation is, in retrospect, a reflection of the plasticity and heterogeneity of DNA, which is made possible by shuffling.

Audience: My question has several parts and is addressed to Professor Sepkoski and Professor Drake. First, what mechanism is behind the rapid increase in number of taxa after a mass extinction? Second, is there some mechanism that prevents the simultaneous existence of more than one intelligent species?

And finally, wouldn't it be very depressing for us humans to come into contact with a civilization much more advanced than ours?

Sepkoski: In answer to your first question, we see rapid evolution following mass extinctions because of a change not in the process but in the boundary conditions. Variations occur all the time, but most of the variations don't survive. Most new species probably arise from small, local, slightly variant populations of existing species. But ecologists have learned that such local populations disappear at phenomenal rates, probably because of competitive pressures that keep them small in size and hence susceptible to extinction. But if somehow the lid of competition is lifted so that populations can expand, then the probability of their extinction goes way down. And then we see rapid increases in number of species.

Turning next to the question about a possible limit on the number of intelligent species, first we need to define intelligence. I prefer an operational definition, as a measure of the ability to control, to re-engineer, the local environment in a nonstereotyped way. mentioned before that a variety of animals can re-engineer habitat, and they are not all even mammals. I think that competition is inevitable if more than one intelligent species exists, and in that competition only one will win, will become pre-eminent. Now I yield to Frank.

Drake: Why is there only one intel

ligent species on the earth? Because of the greed and selfishness of Homo sapiens. The fossil record indicates that at some times more than one intelligent species inhabited the earth simultaneously-Neanderthal man and Cro-Magnon man, for example. The

fossil skulls of those other species often show signs of having been hit with a blunt instrument, and one suspects that it was Homo sapiens who was wielding the blunt instrument, getting rid of all competitors.

The graph of number of species versus brain weight-corrected for body weight is very interesting. For aquatic creatures, particularly aquatic mammals, the curve is continuous. There are species with brains almost the size of those of the dolphins and killer whales, which have the largest brains. But the curve for terrestrial mammals is continuous only up to a certain brain size, then a gap occurs, and beyond that gap there is only one species-Homo sapiens. What created that gap? We did. We eliminated the competition to have the earth to ourselves. That is our nature, and not something to be very proud of. The dolphins and the killer whales have not done the same thing. Terrestrial mammals seem prone to population explosions, and the resulting population pressure leads to fierce competition. But marine mammals do not engage in population explosions. The populations of dolphins and killer whales could expand enormously, since they have very few predators, but for unknown reasons that doesn't happen. So those most intelligent marine mammals have no drive to eliminate near rivals.

In any case one intelligent species dominates the terrestrial ecosystem on the earth. What can be said about the universe? If the other intelligent creatures out there are like us, then they will want to eliminate near competitors. So when they see a new intelligent species emerging, they will stamp it out just as

we stamped out the australopithecines. However, the extreme expense of interstellar travel may be our salvation, since no possible benefit could justify the cost. On the earth inferior cultures have been exploited by superior cultures, as, for example, the Europeans exploited North America and Polynesia. But getting to North America and Polynesia was easy. Going to a distant solar system for self-protection or economic reasons would cost far more than any possible benefit. So the great distances between stars and the laws of physics create a very effective and beneficial quarantine. Intelligent civilizations that far apart can neither exploit nor attack each other. We hope. But they can help each other by communicating. Audience: Today's feats of technology would have been regarded as impossible only a few hundred years ago. So isn't it rash to say that physical contact with other intelligent life is unlikely? Maybe traveling faster than the speed of light is somehow possible, for example. Drake: Yes, we certainly should not neglect the possibility that all the physics relevant to this problem is not known. History raises big red warning flags

about thinking that we know everything. Regarding the question about our egos being demolished by contacting a civilization more advanced than oursand that is the most likely possibility-I don't consider that a problem. We all have been exposed to minds and accomplishments greater than ours. In fact, for most of us that is a continual experience. But the result is more often inspiration rather than depression. I don't believe the human brain is limited in any fundamental way and think it can emulate the power of any intelligence we may find in the universe.

Wald: We humans have stockpiled all the hardware necessary for destruction of our civilization, although at the moment it has not been used. How likely is it that other civilizations have committed suicide with similar hardware and that no one is out there for us to communicate with?

Drake: It has been said that the civilizations we detect will be those that have passed successfully through the nuclear crisis, which will occur in every civilization almost simultaneously with the development of the technology necessary for communication with other civilizations.

Bitensky: Perhaps intelligent extraterrestrial beings are waiting to communicate with us until we prove our worthiness by transcending the nuclear crisis. Wald: The supposition on the part of many people is that the civilizations we might contact would be benign. Is our civilization benign? We grow viruses in our closest mammalian relatives, we slaughter bottle-nosed dolphins by the millions, and we are far from benign even to our fellow humans. It seems to me that we have more to worry about than simply having our egos crushed.

Hubel: What do anthropologists have to say about greed being the cause of extinction of the predecessors of Homo