The timing for the publication of this outstanding volume, which is handsomely produced and illustrated with photos, diagrams, and drawings, could hardly have been better. It appeared at virtually the same moment that a team of scientists announced, at a NASA press conference in the summer of 1996, that a meteorite from Mars contained evidence of ancient extraterrestrial life. Although critics are already contesting the claims made by that scientific team, few critics will be able to dispute the achievement constituted by this book, which brings to a culmination the Cambridge University Press series that began in 1982 with Dick's Plurality of Worlds: The Origins of the Extraterrestrial Life Debate from Democritus to Kant, and that was followed in 1986 by Michael J. Crowe's The Extraterrestrial Life Debate 1750-1900: The Idea of a Plurality of Worlds from Kant to Lowell. The present volume is a truly remarkable achievement, deserving to be read by everyone interested in the history of twentieth century astronomy, in the emergence of fledgling scientific fields such as exobiology (or "bioastronomy") and SETI (Search for Extra-Terrestrial Intelligence), and in the behavior of scientists who explore phenomena at the very limits of empirical science. An astronomer and historian of science at the US Naval Observatory in Washington, DC, Dick has written a book whose erudition, good judgment, and insight place it on the same shelf as the very best works dealing with the history of science.

The book examines how, during the late nineteenth and twentieth centuries, scientists from a number of different fields have speculated about the possibility of and have sought evidence for extraterrestrial life in the solar system and beyond. In describing the struggles of daring scientists to establish research programs based in part on debatable assumptions, Dick elaborates his major thesis: namely, that science cannot adequately be understood as the monolithic culture that C. P. Snow once contrasted so famously with the humanities, but rather must be viewed as involving different cultures. These cultural differences become most evident when natural science is "functioning at its limits. And nowhere are scientists pushed to more extreme limits, by the public and by their own perception of the gravity of the question, than in the extraterrestrial life debate." (p. 7)

Conflicts that have arisen in connection with this debate include defining the place of assumption and speculation in science, and determining whether scarce research funding should be allocated to fields whose hypotheses are scarcely subject to empirical testing. Dick is evidently on the side of scientists who have hypothesized that the universe is biological, i. e., who hold that life is a common feature in any suitable solar system, and who have fought to gain standing for their new field of research, precisely by developing methods to gain the empirical evidence needed to test that hypothesis. Although granting that some of the assumptions made by exobiologists, SETI researchers, and others who adopt the "biophysical cosmology" are probably false, Dick observes:

While exobiological assumptions might be more grandiose than those found in most sciences, they were not qualitatively different, and those who termed exobiology a science without a subject would seem either to have mistaken the nature of science or to have had an agenda of their own. No forefront science could be sure if its subject existed until the observations were made or the experiments undertaken. ...Over whatever period one chooses in the history of science, substantial progress was most often made by making bold assumptions and following leads to their sometimes dead-end conclusions. (p. 545-546)

In Chapter One, after briefly reviewing the history of the extraterrestrial (ET) life debate in Western science, Dick asserts that much subsequent progress in ET research can be attributed to two mid-nineteenth century developments: evolutionary theory and stellar spectroscopy. The latter enabled astronomers to derive significant empirical data about other stars, while the former freed scientists from the shackles of Biblically-based anthropocentrism and creationism, and thus encouraged speculation that there are a plurality of worlds on which life has also evolved. As Dick points out in Chapter Two, however, anthropocentrism did not die easily. Relying on contemporary astronomical research indicating that the sun is near the center of the Milky Way, for example, Alfred Lord Wallace, co-developer of evolutionary theory, argued in 1903 that life could have emerged only on Earth. Although the subsequent findings that the Sun is rather closer to the outer edge of the Milky Way, and that the universe is enormous, had by 1930 tipped the scales in favor of the plurality-of-worlds hypothesis, a number of scientists have continued to hold that the emergence of life on this planet was such an unlikely event that it could almost certainly not be duplicated, even in a universe with billions of galaxies.

In Chapter Three, Dick provides a stimulating review of the search for life in the solar system, with special emphasis on the debate aroused by Lowell's claim to have found "canals" on Mars. Far from denigrating Lowell and others who believed that they saw artificial structures on the Red Planet, Dick concludes that the controversy was difficult to resolve, because "the observations were extremely difficult [with available instruments] and the stakes extremely high, the latter ensuring all possible attempts at resolution." (p. 99) Given that the discovery of life, especially intelligent life, on another planet would probably be the greatest scientific discovery ever made, and would have incalculable effects on human culture, one can well understand why scientists and the general public were gripped by the debate sparked off by Lowell, a scientist with an "ample imagination". The canal controversy exemplifies Dick's contention that science is composed of at least two "extreme" cultures: "the one concentrating on gathering the hard facts and unwilling to go beyond them, the other seeing the hard facts as a basis for a larger theory, with all of the imaginative leaps that this implies." (p. 104)

Even after the canal question was decided against Lowell, in 1924 scientists began debating whether the Martian atmosphere could support the vegetation which some astronomers said could be seen advancing and retreating with the coming of Martian summer and winter. Once again, developments in instrumentation -- especially spectography -- eventually demonstrated that there was far less oxygen in the Martian atmosphere than earlier findings had suggested, thereby casting great doubt on the vegetation hypothesis. By the 1950s, however, new data had breathed new life into this hypothesis. In this debate, too, Dick discerns the presence of two scientific cultures, members of one of which are "much more likely to go out on a limb and to extrapolate than the other." (p. 125) Even after the 1976 Viking mission, which found little evidence in support of Martian life, some scientists continued to hold out for the possibility that life of some form could exist on that planet. Dick's account of the debate about life in the solar system, as well as his detailed description of the debates over what kinds of experiments the Viking mission should carry out on the Martian surface, is fascinating.

The debate carried on between hard-data types and speculators resurfaces in Dick's absorbing account of how debates about the formation of planetary systems (including the birth, death, and resurrection of the nebular hypothesis) influenced the attitudes of early twentieth century astronomers toward the issue of ET life. Sir James Jeans, for example, at one time concluded that life elsewhere was highly unlikely, but toward the end of his life, further astronomical research convinced him to adopt the opposite viewpoint, namely, that ET life was probably common. The ET life debate itself was affected by whether the speculators, i.e., those favoring the idea that planets are common companions of stars everywhere, could gather sufficient data to give credibility to the plurality-of-planets hypothesis. Only very recently has the existence of planets around other stars been confirmed to the satisfaction of most astronomers.

Ever resourceful, Dick tries his hand (successfully) at literary criticism, when in Chapter Five he examines the role played by science fiction both in developing and in expressing modern humanity's deeply felt interest in alien life. Discussing writings by Jules Verne (who, curiously, rarely explored the idea of ET intelligent life), H. G. Wells, Kurd Lasswitz, Olaf Stapledon, C. S. Lewis, Ray Bradbury, Edgar Rice Burroughs, David Lindsay, Stanley G. Weinbaum, John W. Campbell, Arthur C. Clarke, Stanislaw Lem, and Isaac Asimov, as well as popular TV programs such as Star Trek, and films such as 2001: A Space Odyssey, Alien, Close Encounters of the Third Kind, and E. T., Dick points out that a number of scientists were not only attracted to science fiction, which fed their imagination in a way that empirical science could not, but also wrote science fiction. In so doing, such scientists lent credibility to a subject by which much of the public was already fascinated. As Stanislaw Lem, Soviet author of the brooding novel Solaris, once remarked, however, "Man has gone out to explore other worlds and other civilizations without having explored his own labyrinth of dark passages and secret chambers, and without finding what lies behind doorways that he himself has sealed." (p. 259) That envisioning ET life is inevitably characterized by human psychological issues, including projection of good and evil, is evidenced by the commonly polarized representation of aliens as either threatening or benevolent, rarely as neutral parties.

As if taking on science fiction were not a sufficiently risky business for a historian of science, Dick includes a well-balanced and informative chapter on "The UFO Controversy and the Extraterrestrial Hypothesis." While noting that from 1947-1965 the media happily pushed the alien hypothesis to explain UFOs to a gullible public, Dick forthrightly asserts that "scientists in many ways abdicated their role as critical analyzers of an unexplained phenomenon." (p. 269) Concern for personal credibility and difficulties in obtaining reliable empirical data led many scientists to remain silent about UFO sightings, but Dick suggests that the most important obstacle was that "the concept of extraterrestrial intelligence... was not yet a part of the collective scientific consciousness, as it certainly would be in later years." (p. 269, My emphasis.) This assertion leads me to raise the following question: What if the UFO phenomenon had begun to manifest itself not in 1947, but in 1987, after forty years of media hype about ET life, and nearly thirty years after Sputnik spawned the massive federal investment in the Space Program? Would more scientists be willing to investigate the UFO phenomenon, now that their "collective consciousness" has been imbued with interest in ET life? The question is problematic, of course, because UFO sightings that began in 1947 were themselves largely responsible for the subsequent media hype about ET life.

The best chance for serious UFO investigation occurred in the late 1960s, which Dick describes as the "peak" of the ET hypothesis. Spurred by a huge number of UFO sightings, Congress held hearings in 1966 that led the Air Force to sponsor a major study to be carried out by Edward U. Condon. Around this time Donald Menzel was passing the torch of UFO skepticism to Philip Klass, while Northwestern University astronomer, J. Allen Hynek was moving from skepticism to the conviction that UFOs constituted a genuinely new phenomenon worthy of scientific investigation. Meanwhile, James McDonald of the University of Arizona strongly favored the ET hypothesis to explain UFOs, and helped to lead the critical attack against the 1969 Condon Report, in which Condon asserted that UFOs did not merit scientific investigation, despite the fact that members of his own research team had concluded that about one-third of the cases studied could not be explained in terms of known phenomena. Even the American Institute of Aeronautics and Astronautics (AIAA) "turned its back on Condon's conclusions after its own study." (p. 305). Dick emphasizes that the many-cultures dimension of science was nowhere more evident than in the UFO debate in the 1960s.

By 1970, however, despite dissenting voices, scientific interest in the ET hypothesis had begun to wane, for three reasons: 1) no incontrovertible evidence had been found to support the ET hypothesis; 2) ethereal "New Age" theories about UFOs had made study of them increasingly unpalatable for serious scientists; and 3) the "evidence" produced in favor of "ancient astronaut" theories advanced by best-selling authors like Erik von Däniken helped to bring "the entire extraterrestrial hypothesis into disrepute." (p. 308)

Hynek and others countered by suggesting that the ET hypothesis be set aside, not only because it generated unnecessary emotional reactions but also because there was no reason to favor that hypothesis. From Hynek's point of view, UFOs merited study because they could well constitute a new phenomenon unknown to science. Klass and other debunkers continued to insist, however, that UFO sightings could be explained in terms of known phenomena. Increasingly strange claims, including reports that people were being abducted by UFO aliens, made UFO research even more taboo to many scientists. Conceding that career concerns and peer pressure understandably make scientists unwilling to investigate UFOs, Dick goes on to assert

that the desire of some to squash the subject without considering the evidence flies in the face of scientific curiosity that supposedly led them to science to begin with. On the other side, the outrageous claims and hoaxes that presently flood the field are unworthy of scientific attention.... In the middle of these extremes may yet be a phenomenon that requires study, if only one can find it in the midst of the twin human failings in perception and deception. (p. 319)

Chapter Seven offers a superb account of how biological debates about the origin and evolution of life eventually became intertwined with the astronomical search for life on other worlds, so as to give rise to a new scientific field, exobiology, which is still in its infancy. For a long time, many biologists were so convinced of the sheer contingency of life's emergence on Earth that they could not imagine its emergence elsewhere, despite the contention of astronomers that there were probably billions of planets suitable for life. (p. 331) Yet as some biologists became increasingly skeptical that existing hypotheses could explain the origin of life even on Earth, they suggested the "panspermia" hypothesis, according to which life arrived from elsewhere, though this merely pushes the problem of life's origins to somewhere else. (p. 339) In the 1950s, however, Miller and Urey's successful synthesis of amino acids from a mixture of chemicals that supposedly resembled terrestrial conditions at the dawn of life, convinced biologists like George Wald that life will appear anywhere where the conditions are ripe, which would be on many planets in such a vast cosmos. (p. 348) The new gospel of "abundant life" led some biologists to conclude that their discipline, far from being Earth-bound, could attain the same universality as physics and chemistry. Henceforth, exobiology and the study of life's origin on Earth became interconnected, as life on Earth came to be viewed as the result of "normal" evolutionary processes rather than as a singularity.

Despite the early promise of the Miller-Urey experiments, and despite the subsequent discovery by astronomers that organic matter is present in many parts of the universe, critics emphasized that no one had demonstrated how to cross the enormous gap between non-life and life. Such difficulties led Fred Hoyle, Francis Crick, and others to revive the panspermia hypothesis in the 1980s. Others maintained that such an explanation only delays confronting the possibility that purpose, teleology, and design may have to be reintroduced to explain the emergence of a phenomenon as complex as life, since the odds against life emerging by accidental processes are far too great.¹

Evolutionary theorists such as George Gaylord Simpson, Theodosius Dobzhansky, Ernst Mayr, and Steven Jay Gould entered the debate about whether evolutionary theory could be plausibly used in favor of the idea of life on other worlds. Even more daunting than the conceptual difficulties facing the idea that there is such life, is the assumption that human beings could somehow communicate with beings who evolved on other planets. This assumption, however, has driven the remarkable program known as SETI, the Search for Extraterrestrial Intelligence.

SETI enthusiasts proposed to leapfrog problems concerning the origin of life by seeking to make direct contact with ET intelligence. Dick describes in great detail the history of such attempts, ranging from Marconi's claim in the 1920s that he had picked up radio signals from Mars, to early efforts to use radio telescopes in order to pick up possible signals from other planets, all the way to the vicissitudes undergone by SETI proponents seeking to find a place (and a budget) for themselves in NASA. The "Bible" of SETI, I.S. Shklovskii and Carl Sagan's Intelligent Life in the Universe, argued that intelligent life is common throughout the universe and in our own galaxy, but the credibility of SETI was harmed by a second major trend in late-twentieth-century space science: interstellar colonization. Conceptual to proponents of the idea of human colonization of space, if there were any ETs out there, they would have already visited us by now. Since there is no evidence of such visitation (here, of course, as Dick notes, one must set aside the ET hypothesis regarding UFOs), ETs don't exist. SETI skeptics, including Frank Tipler, emphasized the problematic assumptions at work in the famous "Drake equation" often used to estimate the number of communicative civilizations beyond Earth. SETI proponents won points by emphasizing that in science nothing can replace observation when deciding the validity of a hypothesis, and that attempts to make such observation are justified because the stakes are so very high regarding the possibility of ET life.

In Chapter Nine, Dick explains that the protoscience of exobiology (a term coined in 1960 by later Nobel laureate, Joshua Lederberg) followed from the convergence of four separate fields: 1) planetary-spectroscopy, 2) planetary-systems science, 3) radio astronomy and 4) biochemistry. Between 1953 and 1963 these fields themselves "were profoundly transformed in relation to the extraterrestrial life debate." (p. 474) Many scientists have continued to view the whole SETI quest as a waste of time, money, and resources, but Dick concludes that SETI and exobiology "have surely achieved some measure of success in their claims of discipline status," though their greatest achievements presumably lie in the future. (p. 500-501)

Dick explores a host of philosophical and theological themes in his penultimate chapter, which deals with how the discovery of ET intelligence would change the meaning of human life. Ranging from fears that discovery of Earth by an ET race would doom human civilization to hopes that contact with ETs would mean that humankind would become a member of a galactic federation or even achieve a kind of cosmic "salvation", the views expressed by scientists are quite various, a fact that supports Dick's thesis that science is by no means a monolithic enterprise. Consider that, despite natural science's efforts to rid itself of anthropocentrism and teleology, the Anthropic Principle has helped to restore interest in the possibility that the universe exhibits purpose, including the generation of intelligent life capable of reflecting on the origin and meaning of that universe. Nobel laureate Steven Weinberg once concluded that the universe seems pointless, but Dick counters that this conclusion

did not take into account the possibilities inherent in the biological universe, where intelligence, whatever else its characteristics, is likely to be purposeful by definition. What that purpose may be we have not yet the slightest inkling, but if there is a meaning to life on Earth, it is undoubtedly linked ultimately to intelligence in the universe, if this exists. (p. 537)

Although intrigued by the implications of the Anthropic Principle, Dick concludes that many scientists (and the general public) have embraced the idea that evolution is not a one-time event on Earth, but instead that life has arisen throughout this vast universe. This "cosmic Darwinism" may forever end the myth of human specialness, but it makes up for this by suggesting that we are not alone in what has sometimes seemed a lonely universe.

In concluding, Dick reminds the reader that his aim has been to show the many cultures of science as they emerge when scientists are working in "boundary regions", such as those involved in the SETI and exobiology. A host of different sociological and personal factors including worldview and religious concerns, led individual scientists to take up the question of life on other planets. These scientists preferred empirical data, but "did not hesitate to use theory in the absence of observation to further their argument." (p. 548) Even when data were available, scientists read them in a number of different ways (suggesting once again that data are theory-laden). Often, the optimism or pessimism of a particular scientist helped to shape how such data were interpreted.

Presumably, those who are experts about the particular fields studied in such detail by Dick could contest some of his claims, and living participants might have even sharper criticism to make about his assessment of their views and actions. Nevertheless, there can be little doubt that The Biological Universe is a landmark achievement both as a brilliant historical treatment of the search for ET life and as an examination of how this search at the limits of science sheds light on the plurality of cultures within science.

Michael E. Zimmerman
Department of Philosophy, Tulane University
New Orleans, LA 70118

¹In one of the few inconsistencies that I found in this book, Dick observes the following: "If the leap from the synthesis of amino acids to the origin of life was large, the leap from first life to intelligence was, in the eyes of some (although not all), even more monumental. But it is a matter of terrestrial history that chemical evolution not only begat biological evolution, Biological evolution also begat intelligence." (p. 389) In fact, however, that such evolutionary processes occurred is not "a matter of terrestrial history," but instead a current scientific hypothesis to explain the origin of life and intelligent life. Because Dick's own discussion shows that evolutionary theory faces apparently insurmountable obstacles in explaining macroevolutionary events, I am puzzled about why he reasserts (without comment) the validity of the evolutionary hypothesis at this point.

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