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IS LIFE ORIGINATING DE NOVO?* ADOLPH E. SMITHi and DEAN H. KENYONt Recent evidence suggests that the possibility of neobiogenesis should be seriously reconsidered. I. Introduction In 1864, Louis Pasteur declared that living organisms can arise only from parental organisms like themselves and not, as many other investigators had claimed, directly from inanimate matter. Pasteur's carefully conducted experiments were widely believed to have refuted the ancient theory of spontaneous generation, although Pasteur himself stated that the experimental evidence taken in toto could be argued either way [1, p. 187]. It is important to note that Pasteur's experiments were aimed at specific claims of spontaneous generation of microbes involving short periods of time (days, weeks) and very simple starting conditions (boiling organic infusions). He was not concerned directly with either the historical appearance of the first life on the primitive earth or with the possibility of contemporary spontaneous generation in other settings besides sterile infusions. Nevertheless, the spirit of Pasteur's conclusions remained intact during the next seventy years and was accepted by the overwhelming majority of scientists, so that almost no effort was made during this period to find conditions under which spontaneous generation might be possible. Furthermore, the growing body of experience with pure bacterial cultures served to consolidate and strengthen the view that spontaneous generation was not possible. Despite Pasteur's admission that his own data did not absolutely refute spontaneous generation, it would appear that the current reluctance to acknowledge the pos- * We thank the National Research Council (Canada) and the U.S. Atomic Energy Commission for support; and for valuable discussions, Drs. K. Floyd, H. Yonenaka, and W. Keith Hadly. t Physics Department, Sir George Williams University, Montreal 107, Canada. X Department of Cell and Molecular Biology, San Francisco State College, San Francisco , California 94132. Perspectives in Biology and Medicine · Summer 1972 | 529 sibility is based more on unstated beliefs of bacteriological research than on Pasteur's demonstration. Two decades ago an effort started which has shown that, at least in the case of the original appearance of life on the primitive earth, "spontaneous generation," spread over millions of years, very likely did occur. Various mixtures of hypothetical primitive earth gases and liquids produced most of the simpler biochemicals used by life today. Plausible means for the spontaneous appearance of biopolymers and simple microscopic structures bearing some resemblance to living cells have also been demonstrated [2-4]. Although a considerable gap remains between the most complete microscopic structures produced in "origin-of-life" experiments and the simplest free living cells (mycoplasma), we have made very considerable progress in understanding the historical emergence of life from nonliving matter. In 1960, John Keosian raised the possibility of contemporary spontaneous generation of life, that is, the origin of life under present conditions [3]. He proposed the term "neobiogenesis" for such phenomena and attempted to answer some of the objections which are usually raised against the idea. In 'the present paper, we reconsider the hypothesis of neobiogenesis in the light of several recent developments in molecular biology and microbiology: (a) the elucidation of the genetic coding mechanisms and the process by which genetic information is transferred among microbial units of life; (b) the widespread occurrence of mycoplasma in animal hosts and their implication in many diseases; (c) recent data on intimate relationships between animal viruses and their host tissues, especially vertical transmissibility from parent to offspring; (d) recent studies of the spontaneous appearance of organized microstructures in sterile media supplemented with animal sera. We will propose that both mycoplasma and viruses may be originating de novo within cells and tissue fluids of host organisms. We will further suggest that both such newly formed units of life and their "subvital" precursors may play important roles in some disease processes. Our hypothesis is thus an alternative to the view that mycoplasma and virus diseases are caused solely by the invasion into host tissues of preexisting exogenous infectious agents. We will suggest specific experimental consequences of this viewpoint. Since animal mycoplasma have so far been cultured only in serumsupplemented media, we will first examine reports of the appearance 530 I Adolph E. Smith and Dean H. Kenyan · Is Life Originating de...


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