Читать книгу Astrobiology - Charles S. Cockell - Страница 28

There is no doubt that studying the matter that we broadly refer to as “life” is enormously interesting. That is not just because we belong to this subset of matter (although that is certainly one motivation), but because life does do things and exhibits emergent properties that make it interesting as a form of material behavior. In that sense, attempting to refine our understanding of what constitutes and underpins many of these behaviors is an important task in advancing our understanding of this type of matter. However, it may not be possible, or even necessary, to attempt to encapsulate life in definitive single sentences that have no exceptions. Instead, one approach is to formulate operational definitions that broadly capture the type of material we are interested in studying under the term “life.” Joyce's definition, described earlier, is one such approach.

Operational definitions can also circumscribe the type of material we might look for elsewhere in the Universe. For example, to state that one objective of astrobiology is to discover if there are “self-sustaining chemical systems capable of undergoing Darwinian evolution” elsewhere seems like a sound starting point and a reasonable way to agree about the sorts of matter that interest most astrobiologists. Indeed, this definition is a satisfactory basis for the type of material that the rest of this book considers as “life.”

The concept of using working definitions of life may help us resolve some existing problems. For example, the argument about whether viruses are alive is a pervasive one. However, clearly if astrobiologists found virus-like entities on another planet, it would be of enormous interest. Although these entities cannot replicate on their own, and provided they could be shown not to be terrestrial contaminants inadvertently transported to the planet, then their presence would suggest the existence of other perhaps cellular entities, within which they can replicate. From an operational standpoint, the discovery of viruses on another planet would be highly significant. Thus, although we might argue about their place within a definition of life, in terms of the search for life elsewhere, they clearly would fall into the purview of living matter of interest to an astrobiologist. Consequently, from an operational point of view, it seems sensible to include them, and similar sorts of entities, in our quest for “life.”

A working definition of life should not stop us continuing the debate about defining what sort of matter should fall under our category of “life.” Quite apart from refining our understanding of biology, it would be a travesty to destroy some sort of entity elsewhere (if we ever find it) simply because it failed to fit within a narrow definition of life that we have constructed.