Harold Morowitz' forthcoming book, "Metabolism Recapitulates
Biogenesis: The Beginnings of Cellular Life" has a succinct definition
of living systems. To paraphrase from a draft of the book, an
autonomous biological self-replicating system is a molecular
self-replicating entity that is capable of evolving, and that operates
in the absence of other self-replicating entities. Therefore, a virus
is not an autonomous biological self-replicating system because it
requires the presence of other self-replicating entities to replicate.
Whether it is alive or not depends on whether you equate life with an
autonomous biological self-replicating system, or simply a biological
self-replicating system.
For more details, see Chapter 8 of the book.
Peter
