Science in Christian Perspective
From: JASA 17 (June
Experimental work bearing an the origin of life continues to appear in scientific journals and two major symposia have now been published. In this paper three different reviews of the subject are discussed to indicate not only the current status but. also the varying attitudes of investigators toward accomplishments in the field. The influence of the space program and the lively conflict over exobiology are pointed out.
The subject of the origin of life has been reviewed by the present author several times in recent years,1,2 but has not been discussed at an Annual Convention of the ASA since the symposium at the 1957 Convention at Gordon, College.3 For those who wish an introduction to the subject, these published reviews, particularly the chapter in the monograph Evolution and Christian Thought Today' (or some of the semi-technical references cited therein) should serve the purpose fairly well.
For those with some technical background who wish to examine the scope of investigation in this field, the standard reference work is Volume 1 of the Interna tional Union of Biochemistry Symposium Series, proceedings of the first international symposium on the subject, held in Moscow in August, 1957. The EnglishFrench-German edition (with most of the papers in English) was published in 1959, a 700-page book edited by A. I. Oparin and other Soviet scientists and entitled The Origin of Life on the Earth.4 Major areas of concentration in this field are indicated by the titles of the sessions of this historic symposium:
(1) Primary formation of primitive organic compounds on the earth.
(2) The transformation of primary organic compounds on the earth.
(3) The origin of proteins, nucleoproteins, and enzymes.
(4) The origin of structure and metabolism.
(5) The evolution of metabolism.
In each of these areas competing theories still flourish, stimulating a wide variety of experimental approaches. It is clear by now that the problem of the origin of life is as vast as the problem of the evolution of living forms, and that no single experimental success, no matter how impressive nor how dramatically publicized, can settle all the many questions yet unanswered in this field.
As a sequel to the 1957 Moscow symposium, a meeting was held in October, 1963, in Wakulla Springs, Florida, on the origin of prebiological systems. The papers have only recently appeared in print20 but a brief report with some indication of the content of each paper was promptly published in Science.5 In general the papers fall into the above categories, but several new developments are apparent. For one thing the field has matured sufficiently for workers in it to see the need for clarification of terminology; the geneticist T. Dobzhansky, for example, who served as interpreter for A. I. Oparin's paper, at one point took great exception to use of the term "natural selection" for prebiotic phenomena in addition to its use in the traditional Darwinian sense. Another feature distinguishing the 1963 symposium from its 1957 predecessor was acknowledgment of the importance of space technology for scientific investigation of the origin of
*Walter R. Hearn Is Associate Professor In the Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa.
life. Indeed, the 1963 conference was sponsored jointly by the Institute for Space Biosciences of Florida State University and by the National Aeronautics and Space Administration (NASA), which maintains at its Ames Research Center in Mountain View, California, a large Exobiology Division. We will return to space technology and extraterrestrial life in a moment.
Investigators on the origin of life differ not only in their theoretical preferences and experimental approaches but also in their evaluations of the status of the field as a whole. To indicate these attitudes as well as accomplishments in the field, attention will be called primarily to three review articles by leading investigators, published in 1962, 1963, and 1964 and revealing attitudes which might be called pessimistic, realistic, and optimistic, respectively.1962: Horowitz and Miller
The 1962 review, by N. H. Horowitz of Cal Tech and Stanley L. Miller of the Oceanographic Institute at La Jolla, is entitled "Current Theories on the Origin of Life." It is in English but published in a tri-lingual annual called Fortschritte der Chemie organischer Naturstoffe (Progress in the Chemistry of Organic Natural PrGducts).6 Stanley Miller, you may recall, was the graduate student of Nobel-laureate Harold Urey whose 1953 paper, "A Production of Amino Acids Under Possible Primitive Earth Conditions",7 in a sense triggered off the modern phase of research on the origin of life. It is rather surprising, therefore, to encounter the decidedly cautious and negative tone in this recent review article by Horowitz and Miller. The article never describes an accomplishment in the field without emphasizing the tremendous gaps remaining in our knowledge, and criticizes essentially all major competing theories, seldom setting forth an alternative.
In discussing minimum criteria for living matter, these authors conclude that an organism, to be called living, must be capable of both replication and. mutation; the underlying pessimism of their review may stem from choosing a definition of living matter somewhat more encompassing than the working definitions used by others in the field. That is, having posed a larger problem, they see the solution to it as relatively more remote. A model DNA-RNA-protein system fulfills their minimum requirements for a living system and is simple in comparison to a whole cell, but they consider it still too complex and too efficient to have originated spontaneously by random chemical reactions; this system must itself be the product of a long evolution. The original, primitive genetic system may have been so different from the highly evolved system that they would bear little resemblance, but we have no experimental evidence to settle this point. There is much speculation that the first living organism consisted of a polynucleotide which produced or was associated with a polymerase, but the authors point out that even this hypothesis is not as simple as it appears. For one thing, degradative reactions have to be assumed which would result in a low, steady-state concentration of biologically significant polymers. At the present time we have no way of judging whether the origin of life was an extremely improbable event or the inevitable outcome of the evolution of organic compounds on the primitive earth.
Instead of presenting enthusiastic arguments for the reducing character of the primitive atmosphere, these authors say it would probably not be necessary to accept the hypothesis of a reducing atmosphere if organic compounds could be synthesized under oxidizing conditions; apparently they cannot. However, under reducing conditions, with essentially any kind of energy source, organic compounds are produced. A table of present energy sources averaged over the earth is presented to make the point that electric discharges from lightning and corona effects amount to about four calories per square centimeter per year, essentially the amount of ultraviolet radiation in sunlight at 1500 Angstroms (there is much more UV energy at longer wavelengths: 75 cal/CM2/yr at 2000 A, and 570 cal/CM2/yr at 2500 A). For formation of free radicals from methane, water, ammonia, etc., wavelengths below 2000 A are needed; larger organic molecules formed in photochemical reactions in the upper atmosphere would absorb at longer wavelengths and thus might not reach the oceans before being decomposed by absorption of ultraviolet light. It is not surprising that the types of organic compounds formed in experiments with electric discharges are identical to those formed when short-wave UV light is used as the energy source, since the same reactive aldehydes and hydrogen cyanide are formed from free radicals in either case. Cosmic ray energy is negligible at present and although 4 x 109 years ago radioactive disintegration was more important, most of that form of energy was expended on the interior of the rocks and not available for reactions in the oceans and atmosphere. The energy from volcanoes was relatively insignificant and localized.
and Miller are critical of Sidney Fox's argument that thermal reactions were
important on the primitive earth; they discount John Oro's syntheses of adenine
and other biologically important compounds from ammonium cyanide solutions on
the basis that his concentration of ammonium cyanide (1.5 M) would have been
impossible in the primitive ocean. Other problems, such as the origin of optical
activity in biological systems, are discussed in the same pessimistic vein. In a
final section on space research, however, these authors show considerable
optimism over the possibility of finding out whether life exists on other
planets. A fundamental question which might be answered by space exploration is
whether a form of living matter is possible which is not based on nucleic acids
and proteins; the implications of this question were discussed in 1960 by Joshua
Lederberg.8 But even if life is not found on the moon or Venus or
Mars, the possibility of examining the organic compounds on their surfaces or in
their atmospheres may yield invaluable evidence bearing on the. origin of life
an the earth, according to these authors.
Ekobiology: A Digression into Outer Space
It may be appropriate to digress here for a brief look at our actual plans for detecting life on Mars and Venus as described in a 1963 NASA pamphlet on "The Search For Extraterrestrial Life."9 It is generally assumed that though they now differ, in their earliest stages the atmospheres of all the planets were the same as that postulated for the primitive earth; hot gases of hydrogen and hydrogen compounds such as methane, water vapor, and ammonia, with the possibility of some carbon dioxide. The composition of this atmosphere gradually changed. The gravitational attraction of the earth was not sufficient to hold the lighter gas molecules so they escaped into space. The moon, with feeble gravitational attraction, was unable to hold any atmosphere at all. Jupiter and Saturn, much larger than earth, retained atmospheres of hydrogen and hydrogen compounds. Mercury, close to the sun, is probably too hot for any form of life. Jupiter, Saturn, and other planets far from the sun are probably too cold.
Spacecraft have now been sent past the moon and actually landed on the moon. Mariner 2, launched from Cape Canaveral on August 27, 1963, flew past Venus on December 14, 1963, taking readings and transmitting data which may have significance in the search for extraterrestrial life. Mariner's measurements showed temperatures on the surface of Venus on the order of 800 degrees Farenheit, too hot for life as known on Earth; however, temperatures at the top of the Venus cloud level are about -40deg. F. Could there be some form of life in the atmosphere between these levels?
Mars and earth both orbit the sun in the same direction but not at the same speed or distance. The mean distance of earth from the sun is 90 million miles; the mean distance of Mars from the sun is 141 million miles. Earth makes one revolution about the sun each 365% days; Mars takes 687 earth days for the same trip. The distance between Mars and the earth varies from 62 million miles down to 34 million miles when their orbits are in favorable opposition. After a failure by Mariner 3, the Mariner 4 spacecraft was launched toward Mars by NASA aboard an Atlas Agena rocket on November 28, 1964. If all goes well, this 574-pound planetary flyby will provide information for later attempts to detect life on Mars: as it sails within 10,000 miles of the planet it will transmit to earth high quality television pictures along with measurements of magnetic field strength, infrared spectra, and other data. A subsequent Mariner was originally scheduled to land a life-detecting instrument package on the Martian surface by parachute in 1966 or 1967, but these plans have been changed radically and postponed until at least 1969. What sort of instruments might such a package contain?
Eight devices now under development for detecting evidence of extraterrestrial life are described in the NASA pamphlet. One device measures optical rotatory dispersion in the ultraviolet region: if a sample of Martion soil absorbs at 26M A without optical activity, the baso adenine from pre-biological syntheses may be assumed to be present, but if a large optical rotation is associated with that wavelength, the adenine will be assumed to be linked to an optically active sugar in the nucleic acid molecule and life on Mars will be inferred from the signal transmitted to earth.
Another type of ultraviolet spectrometer is being developed to search for the absorption at 2000 A characteristic of the peptide bond of proteins.A device called a "multivibrator" is being developed by Dr. Lederberg at the Stanford Medical Center: it is essentially a set of incubation chambers into which soil samples can be blown for the detection of enzymatic activity. Breakdown of various substrates to easily detected radioactive or fluorescent products will indicate the presence of bacteria in the soil samples.
Another scheme of Dr. Lederberg's is a microscope with fixed-focus lens, an illuminator, a soil collection system, and a vidicon camera to take an actual look at any organisms present; it is believed that a microscope able to cover an object field of 100 microns with resolution of 0.5 micron, a one-watt illumination source, and a vidicon camera with a 200 line scan to match the resolution of the lens system can be combined in a package which will weigh less than three pounds, have a volume of less than 500 cubic inches, and be capable of standing both the trip and the sterilization necessary to prevent contamination by Mars by microorganisms from the earth. Another device is essentially a colorimeter with a monochromator set to measure an intense absorption peak known as the "J-band" of a solution of cyanine dye, a band which shifts when the dye is complexed with protein; if the J-band detector radios back to earth a spectral shift when Martian dust is introduced into the dye solution, the presence of proteins will be inferred, possibly from viruses, bacteria, fungi, algae, spores, or pollen.
A device nicknamed "Gulliver" has been tested several times already on earth; it consists of a chamber containing a universal culture broth made radioactive and three small cannons which shoot "sticky strings" out 50 feet and then reel them back into the culture chamber. If bacteria are present on any of the strings they begin to grow and multiply and produce radioactive gas which is detected by a miniature Geiger counter near the culture chamber; in this case as in some of the others the signal will be sent by transistorized radio to the "bus" or orbiting space capsule from which the package was dropped to the surface of Mars, and the "bus" will transmit to earth with its heavier radio equipment. Another type of "bug detector" being designed by Professor Wolf Vishniac has been nicknamed the "Wolf Trap"; it uses a vacuum chamber to suck atmospheric dust into a culture medium where changes in turbidity and pH can be measured with time.
Finally, an attempt is being made to miniaturize a mass spectrometer so that the range of molecular fragments vaporizing off a sample of Martian dust near the ion source can be scanned quickly; if amino acids, peptides, or proteins similar to those of living things on earth are present on Mars they should give mass spectra similar to those of samples tested on earth. The Chief of Exobiology Programs for NASA says that this device may even be able to detect a form of life as we do not know it on earth if complex life-related substances unlike our familiar earth-bound organic compounds are discovered.
Since the moon has no appreciable atmosphere, its surface may be a museum of cosmic dust captured by its gravitational field and left undisturbed by atmospheric or biological alteration. In a 1958 paper with perhaps the shortest and most fascinating title in all scientific literature-"Moondust"10-Dr. Lederberg and Dean B. Cowie argued that the record of cosmic history contained in the dust on the moon should be as valuable for understanding the biochemical origins of life as the fossil-bearing sediments of the earth's crust have been in understanding life's subsequent evolution. Lederberg and Cowie expressed concern lest future scientific investigation of the moon and of other celestial bodies be ruined by contamination from interplanetary missiles from earth. A committee has now been set up by the International Council of Scientific Unions under the chairmanship of M. Florkin of Belgium to study this problem.
The reciprocal problem posed by the future possibility of round-trip space flight has also been discussed by Lederberg.8 The dramatic hazard of introducing a disease-producing organism from another planet can no longer be relegated to science fiction. Although it can be argued that earthly disease-producing organisms have generally had to evolve very elaborate adaptations to resist attack by human defense mechanisms, it can also be argued that an infective organism to which our defenses have not been adapted through previous contact might prove to be beyond our powers to cope. The risk of pandemic disease, while extremely unlikely, is also immense. Exobiology is no more fantastic than the realization of space travel itself, according to Professor Lederberg.
In contrast, George Gaylord Simpson in a 1964 article entitled "The Nonprevalence of Humanoids"11 ridicules the whole field of exobiology, arguing that this new "science" has yet to demonstrate that its subject matter even exists! Simpson concludes that (1) there are certainly no humanoids elsewhere in our solar system; (2) there is probably no extraterrestrial life in our solar system; although some form of life may occur on Mars; (3) because of the vast number of stars in the universe, the highly improbable development of life undoubtedly has occurred in other planetary systems, but even so it is extremely unlikely that we shall ever learn of its existence; and (4) it is nearly impossible that life anywhere in the universe includes humanoids and even less possible that we could ever communicate with them in a meaningful way even if they did exist. According to Simpson, spending money to discover extraterrestrial life is a gamble at the most adverse odds in history which even if successful can teach us only little about life. His article ends on a pleading note:
But we already have life, known, real, and present right here in ourselves and all around us. We are only beginning to understand it. We can learn more from it than from any number of hypothetical Martian microbes. We can, indeed, learn more about possible extra-terrestrial life by studying the systematics and evolution of earthly organisms. Knowledge from enlarged programs in those fields Is not a gamble because profit is sure. My plea then Is simply this: that we invest just a bit more of our money and manpower, say one. tenth of that now being gambled on the expanding space program for this sure profit.
Simpson's chilling blast in February, 1964, drew a series of critical replies published in Science in May.12 Also that May, the AIBS bulletin now called BioScience carried a report13 of a Space Biology Workshop convened in January, 1964 by AIBS and supported by NASA at the Space Sciences Center of the University of Rochester. According to the report by Wolf Vishniac and Richard Lewontin of the Rochester Center, thirty of the nation's prominent biologists unanimously agreed that "The search for extraterrestrial life is the single most important question to be answered by the space age." In June, 1964 a BioScience editorial "On Exobiology"14 reported these conflicting opinions about space biology programs and described hardware difficulties which caused the 1964 Mars life-detection shoot to be postponed until the next "window" or favorable launch opportunity in 1966. Furthermore, a reevaluation of the Mars spectrum has now led to the conclusion that the atmosphere on that planet may be as low as ten millibars, an order of magnitude lower than the previously accepted value; the lower pressure would make parachuting an instrument capsule from a "bus" impossible and adding retro-rockets to the capsule might reduce the payload to the marginal point. NASA has revealed that a 1966 life-detection mission is out; Congress, tired of perennial increases in NASA appropriations, has left a total funding of $7,000,000 for exobiology, possibly inadequate to prepare even for a 1969 mission. After 1969 there will be 19 windows" to Mars in 1971 and 1973, but after 1973 oppositions between Mars and earth become unfavorable for a decade.131963: J. Oro
This would mark the end of our digression into outer space except for the fact that the second review paper to be considered, John Oro's realistic "Studies in Experimental Organic Cosmochemistry,"15 appears in a symposium with an extraterrestrial theme: "Life-like Forms in Meteorites and the Problems of Environmental Control on the Morphology of Fossil and Recent Protobionts." This June, 1963 issue of the Annals of the New York Academy of Sciences contains papers presented at a conference called in April, 1962, primarily to deal with the claims of Bartholomew Nagy of Fordham University and his NYU colleagues that "organized elements" they found in the Orgueil carbonaceous chondrite were clear-cut evidence of extraterrestrial life. The published symposium carefully arranged with three papers by Nagy at the end for obvious climactic effect, must now be a source of embarrassment to its overzealous organizers; Frank Fitch and Edward Anders of the University of Chicago, who argued against Nagy's claims at the conference, have smice convinced most people that some of the "organized elements" on the century-old meteorite were biogenic all right-but earthly contaminants--and the rest merely mineral grains.16 A spiny type of "hystrichospherid" on the Orgueil meteorite was identified by several investigators as ragweed pollen! Judging by the condensed report appended to the published symposium, the final discussion chaired by Harold Urey must have been a riot-or nearly so.
The rationale for including Oro's down-to-earth paper on organic cosmochemistry in this bizarre symposium was probably to show that the small percentage of organic matter (7 per cent in an Orgueil sample) in the nineteen known carbonaceous chondrites might be of prebiological if not biological origin. Oro's 1963 review stands on its own, however, as a balanced and thorough review (with 182 references) of experimental work relating to prebiological syntheses of organic compounds of biological significance. Amino acids, hydroxy acids, monosaccharides, parines, pyrimidines, polypeptides, and polynucleotides have now all been produced experimentally in model systems simulating reasonable primitive atmospheres. Oro points out that his own "cometary" model, Urey's "primitive planetary atmosphere" used by Miller, and Sidney Fox's 44volcanic atmosphere" model should be considered as complementary rather than alternative approaches to study of the prebiological formation of organic compounds on earth.
The implications of Oro's choice of a cometary model are quite interesting, since the composition of present comets is considered to reflect approximately the composition of the primordial solar nebula and protoplanets. The spectra of comets show fluorescence emission bands corresponding to the molecules or radicals CN, CH, CH2, C2, C3, NH, N112, and OH, to the radical ions CH+, OH+, CO+, N2+, and C02~, and to the atoms of Fe, Ni, Cr, and other elements; Oro's simplified experimental model contains HCN, NH3 and H20-and this mixture produces adenine and its biological precursor 4-aminoimidazole-5-carboxamide!
Possibly because we take inorganic chemistry as freshmen, organic chemistry in our junior year, and biochemistry only in graduate school, it may be hard for us to think of organic and biochemical compounds as being fundamental components of the universe. Yet, with the exception of the noble gases the four most abundant elements in the universe are hydrogen, oxygen, carbon, and nitrogen, precisely the four major elements of organic compounds and of living matter.
Indeed, Oro reminds us that the composition of living matter is a better sample of the universe than is our earth! The assumption that the earth was formed from a gravitationally undifferentiated protoplanet implies that organic chemistry was already going on at the very beginning of the primitive earth.
Before turning to the final review article on the origin of life, we might call attention to several other papers of interest in the "meteorite-inicrobe" symposium. Sidney Fox17 of Florida State University as usual reviewed his own work on proteinoids of thermal origin, with impressive photographs to illustrate their precellular I'morphogenicity" and hints of their catalytie aq tivity. Along a different line was the report of "Bacteria from Paleozoic Salt Deposits"18 by Heinz Dombrowski of the Department of Balneology of JustusLiebig University in Giessen, Germany: for the first time it has been possible to isolate and cultivate bacteria from Permian, Middle-Devonian, Silurian, and even Precambrian salt deposits, creatures having lain dormant for from 180 million years (Permian) to 650 million years (Precambrian). Bacteria from the Precambrian and Silurian salts showed fewer biochemical abilities than the "younger" Permian organisms. Ages of most of the deposits were established from characteristic fossil pollen grains and found to be in accord with geological features. Careful precautions to avoid contamination were taken and apparently these astounding findings have not been challenged by other investigators.1964: Calvin and Calvin
The 1964 review of the origin of life categorized earlier as optimistic was written by Nobel-laureate Melvin Calvin of the University of California at Berkeley and his wife Genevieve. It is entitled "Atom to Adam," a lecture given by Dr. Calvin before the American Philosophical Society in November, 1963; it appeared in the June, 1964 issue of American Scientist.19 Calvin's minimum criteria for living matter are slightly different from Horowitz and Miller's; they are (1) transfer and transformation of energy and (2) transformation and communication of information. The major argument of the paper is as follows: the problems of prebiological synthesis of biological monomers and polymers are essentially solved; furthermore, the structural information in three-dimensional polypeptide and polynucleotide molecules required by the two criteria for living matter is contained ultimately in their monomeric sequences. This argument is supported by reference to the reversible destruction of secondary, tertiary, and quaternary structure of various enzymes, and to the reversible uncoiling or "melting" of DNA. Calvin postulates that even visible structures such as collagen fibrils may be the direct resultant of primary structure, and stops just short of saying the same thing about cellular units such as ribosomes and mitochondria.
A review of the DNA-RNA-protein system for "molecular communication" leads Calvin to consideration of environmental control of genetic expression. How do different cells of an organism know they have different functions when they all have the same kind of DNA? What tells the individual cells which parts of their DNA to read? At this point Calvin speculates on what might be accomplished if our present knowledge of manipulating genetic information in bacteria (such as introducing new genes by transduction, or controlling expression of existing genes by simple molecules as in enzyme induction) can be extended to the human level. For example, the ten billion brain cells with which a human being is born might be increased to 100 billion by controlling the growth of various developing cells in the embryonic brain, maybe even allowing us to keep ahead of electronic eomputers in the future! More practical, no doubt, is control of virus disease, cancer, and the adaptability of man; we may someday have the power to intensify certain human traits, delete others, and perhaps even develop new ones. The chemical control of men's minds is approaching already. Calvin's optimistic spirit is maintained right up to the staggering question: "Who is going to change men, and how many of them, and in what way?" He concludes his review of the origin and development of life with these statements:
The distance from Atom to Adam covers billions of years. But following the laws of the behavior of matter, the process has been orderly, even in Its infinite complexity. But during these years, the laws of nature have functioned In a laboratory in which each atom has its destiny, but within which no encompassing comprehension of the whole could sway the course of experiment.
Today, the world is quite as awesome to contemplate as it must have been in its beginnings, for today man Is here and he has a little knowledge! With each thread of new truth, the responsibility to weigh the consequence of its application becomes more critical. The rate of evolution can change tremendously with man's new knowledge, and the responsibility to control the rate and the direction of change must depend on wisdom. As it has to this day, time will record our success-or our failure.In the above quotation which leaves the realm of science and enters the realm of philosophy to speak of destiny, awe, responsibility, wisdom, success, and failure-I personally see a primary reason for us as evangelical Christians to pay serious and respectful attention to Experimental Work Bearing on the Origin of Life, the title of this paper. It is clear to me as a biochemist that this field will continue to develop, with or without adequate NASA support. It is clear to me as a Christian that its development will continue to bring scientists face to face with the perennial theological questions to which we claim the Gospel of Jesus Christ provides necessary and sufficient answers. If we show respect for the work in this field and for the workers in it we shall in turn command respect for the testimony which we bear. Having followed Professor Calvin's scientific arguments I am not obliged to agree with his philosophical position. In fact, I do not agree with him philosophically, for I believe that God, the Creator, does possess an "encompassing comprehension of the whole" and indeed has "swayed the course of experiment" at every turn. When scientists, even Nobel prize-winners, seek wisdom, shall we not be ready to tell them of its Source? "For the fear of the Lord is the beginning of wisdom."
1. Hearn, W. R., and R. A. Hendry, The Origin of Life. In: R. L. Mixter, Ed. Evolution and Christian Thought Today. Grand Rapids: Eerdmans. 1959.
2. Hearn, W. R., Origin of Life, J. Am. Scientific Affiliation 13, 38 (1961).
3. Hearn, W. R., The Formation of Living Organisms From Non-Living Systems. J. Am. Scientific Affiliation 10, No. 2, P. 2 (1958).
4. Oparin, A. I., A. E. Braunshteln, A. G. Pasynskli, and T. E. Pavlovskaya, Eds., Proceedings of the First International Symposium on the Origin of Life on the Earth. New York: Pergamon Press. 1959.
5. Young, R. S., and C. Ponnamperuma, Life: Origin and Evo. lution. Science 143, 384 (1964).
6. Horowitz, N. H., and S. L. Miller, Current Theories on the Origin of Life. Fortschr. Chem. organ. Naturstoffe 20, 423 (1962).
7. Miller, S. L., A Production of Amino Acids Under Possible Primitive Earth Conditions. Science 117, 528 (1953); J. Am. Chem. Soc. 77, 2351 (1957).
8. Lederberg, J., Exobiology: Approaches to Life Beyond the Earth. Science 143, 384 (1964).
9 , National Aeronautics and Space Administration, The Search for Extraterrestrial Life. Washington, D.C.: U.S. Govt. Printing Office. 1963-M91-542. 20 pp. 20c.
10. Lederberg, J., and D. B. Cowie, Moondust. Science 127, 1473 (1958).
11. Simpson, G. G., The Nonprevalence of Humanoids. Science 143, 769 (1964). Reprinted from This View of Life, Harcourt, Brace and World, Inc., New York.
12. Pfeiffer, J., and H. F. Blum; M. F. Halasz; L. Ornstein; G. G. Simpson; Life on Other Planets: Some Exponential Speculations (Letters). Science 144, 613 (1964). Fox, S. W., Humanoids and Proteinoids (Letter). Ibid. 144, 954 (1964).
13. Vishniac, W., and R. Lewontin, Report of Space Biology Workshop, January 9-10, 1964. BioScience 14, No. 5, p. 63 (May, 1964).
14. On Exobjology (Editorial). BioScience 14, No. 6, p. 7 (June, 1964).
15. Oro, J., Studies in Experimental Organic Cosmochemistry. Ann. N. Y. Acad. Sci. 108, 464 (1963).
16. Fitch, F. W., and E. Anders, Organized Elements, Possible Identification in Orgueff Meteorite. Science 140, 1097 (1963). Anders, E., and F. W. Fitch, Search for Organized Elements in Carbonaceous Chondrites. Ibid. 138, 1392 (1962).
17. Fox, S. W. and S. Yuyama, Abiotic Production of Primitive Protein and Formed Microparticles. Ann. N.Y. Acad. Sci. 108, 487 (1963).
18. Dombrowski, H., Bacteria From Paleozoic Salt Deposits. Ann. N.Y. Acad. Sci. 108, 453 (1963).
19. Calvin, M., and G. J. Calvin, Atom to Adam. Am. Scientist 52, 163 (1964).
20. Fox, S.W., Ed., The Origins of Prebiological Systems and of Their Molecular Matrices. New York: Academic Press. 1964.