Biología

CHEMISTRY & BIODIVERSITY – Vol. 5 (2008)

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REVIEW What Is Life?
A Brief Historical Overview
by Antonio Lazcano Facultad de Ciencias, UNAM, Apdo. Postal 70-407, Cd. Universitaria, 04510 Mexico, D.F., Mexico (e-mail: alar@correo.unam.mx) Dedicated to the memories of Leslie E. Orgel and Stanley L. Miller

1. I Sing the Body Electric. – After many years of experimentation on the effects ofelectricity on frog legs, in 1791 Luigi Galvani published his Commentary on the Effects of Electricity on Muscular Motion, summarizing the observations that had led him to believe in the existence of animal electricity that originated in the brain, and traveled through nerves and muscles. A child of the Enlightenment, Galvani was no mystic, and the fascination that his observations awoke in both hiscolleagues and the lay public (which are echoed in Mary Wollstonecraft Shelleys masterpiece Frankenstein) must be understood as part of the process of secularization that life sciences underwent through this period: Galvani was, in fact, attempting to explain the nature of life itself on the basis of a purely physical phenomenon. As shown by the 19th century efforts to describe the basicproperties of life on the basis of magnetism, surface tension, radioactivity, and other physical phenomena [1], Galvani and others had initiated a scientific trend that has continued for over two centuries. In a way, Erwin Schroedingers famous book What is life? [2] can be seen as part of this trend. Schroedingers text should be read not as the starting point of the appeal that biological phenomena hadover many physicists, but rather as the culmination of a long tradition that attempted to explain the nature of life in physical terms. What is generally not realized is that Schroedinger did not include in his book a single reference to biology. This is quite surprising, especially since many of his contemporaries were already having important insights when addressing basic properties of life suchas heredity. A few years before What is life? was published, for instance, John B. S. Haldane wrote that ...two possibilities are now open. The gene is a catalyst making a particular antigen, or the antigen is simply the gene or part of it let loose from its connection with the chromosome. The gene has two properties. It intervenes in metabolism, sometimes at least by making a definitivesubstance. And it reproduces itself. The gene, considered as a molecule, must be spread out in a layer one building block deep. Otherwise it could not be copied. The most likely method of copying is by a process analogous to crystallization, a second similar layer of building block being laid down on the first. But we could conceive of a process analogous to the copying of a gramophone record by theintermediation of a negative perhaps related to the original as an antibody to an antigen... [3].
 2008 Verlag Helvetica Chimica Acta AG, Zürich

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CHEMISTRY & BIODIVERSITY – Vol. 5 (2008)

2. From Primordial Enzymes to Ancestral Nucleic Acids? – The same year that Schroedingers book appeared, the seminal paper by Avery, McLeod, and McCarty [4] on the role of nucleic acids in hereditaryphenomena was also published. Its publication marks the starting point of the extraordinary developments of molecular biology that have firmly established the central role that nucleic acids have in all cells. Perhaps not surprisingly, its publication would eventually lead to the reinforcement of previous attempts to define life solely in genetic terms. In a series of papers published during the FirstWorld War, the American physicist Leonard Troland [5 – 7] had argued the origin of life was due to the random formation of a self-replicating enzyme-like molecule that had made its sudden appearance in the primitive oceans. A few years later Hermann J. Muller, an American geneticist who would play an important role in the understanding of Mendelian heredity, explicitly adapted Trolands hypothesis...