Approaches to the definitions of life

This negative attitude has several components, which have been partly analyzed (Luisi, 1998). One main problem is that the term life is too vague and general, and loaded with a number of historical, traditional, religious values. In particular, in the Christian tradition, the term life is generally linked to the notion of soul -and in Buddhism is linked to the notion of consciousness. 

Of course, this is too much of a big picture and to define fife at this level may indeed appear impossible. However, one can scientifically tackle this question by looking at life in its simplest expression, namely microbes and other uiucellular organisms. This is a first, important clarification, which also eliminates (at least for most scientists) the notions of soul or consciousness from the picture. In other words, let us talk only about microbial fife, and try to give a definition of cellular life. 

Another difficulty in attempting to give a definition of life is that in fact the term definition is too ambitious, too frightening. Probably the term description would be more acceptable. In the language of epistemology, there is the distinction between an intrinsic description, meaning a context-independent description based on first principles and an operational description. As Primas says in a different context (Primas, 1998)  

Actually, most of the definitions of life given in the literature comply to the above operational description. In the following pages, the term dehnition is used mostly as a way of habit, meant however in the above epistemological context. 

However, I still think - despite these intrinsic difficulties - that it is important to debate the question of the detiitition of life, both from an intellectual and a practical point of view. Everyone working in the held of the origin of life should be able to provide their own definition (or description) of life, simply because they work experimentally or theoretically on models of minimal life and they should state and define the subject of the inquiry and the final aim of the work. This corresponds already to a kind of definition of life. Considering the number of authors in the held, this may correspond to quite a large number of different research projects, but all should adhere to the same basic constraints. What are these  

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Approaches to the definition of life Table 2.1. The game of the two lists... 

System qualification is a process that ensures that an analyzer system is installed and operated according to requirements that are aligned with the intended use of the system. The commonly used approach in the pharmaceutical industry is the system life cycle or SLC process. In the SLC approach, the definition of intended use, design, configuration, installation and operation is linked and documented over the lifetime of a system. 

I have stressed in this book that one of the main reasons why the bottom-up approach to the transition to life has not been corroborated experimentally lies, among others, in the fact that the sequence of our macromolecules of life - enzymes, RNA, and DNA - are the products of the vagaries of contingency and by definition it is then impossible to reproduce them in the laboratory. 

Artificial life is an entirely new approach to the fundamental problems of biology, because it allows us to study life in a totally different way, i.e. by building machines that have some of its properties. It must be underlined, however, that silicon-based life is utterly different from carbon-based life because artificial molecules and artificial cells are made of electronic circuits and are therefore two-dimensional creatures. This explains why biologists have not abandoned more traditional approaches, and the search for a proper definition of organic life has never stopped. In this field, an important step forward was made in 1974 by Francisco Varela, Humberto Maturana and Ricardo Uribe, with the paper that introduced in biology the concept of autopoiesis. 

Yes, hexoses are too bulky base pairing in the Watson-Crick mode of hexose analogs of RNA runs into steric difficulties. This is a relatively solid result in this kind of work after all, research on molecular evolution cannot be expected to reach conclusions that are as definite as those in normal chemistry. This type of inquiry and experimental strategy will gradually allow us to approach a question that science will have to ask sooner or later, namely, whether the chemical uniqueness of life, as we know it, is intrinsic or accidental. For the time being, inquiring about the uniqueness of life is premature, but this may change some time in the future. 

Nevertheless, despite these warnings, the questions are of supreme interest. Given that life bends the rules, a slight digression is warranted. A definition of life is perhaps best approached via thermodynamics (Nisbet, 1987). Life is growth— it is always in disequilibrium with its surroundings, and its actions are such as to increase that... 

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