article in this week's The Scientist takes a look at the old problem of just what exactly is life? Drawing on some recent papers they suggest that it is self reproduction with variation that is key.
The hypothetical primitive RNA replication process has a degree of
sophistication that separates it from mere chemistry: it copies itself
and allows copying mistakes, which themselves are copied in future
generations. In other words, this is the process of self-reproduction
with variations (as in Spiegelman’s system), not just organic
synthesis. This is the very definition of life suggested by the
developing theory of early molecular evolution. The same
formula is derived by “word count” analysis, which yields the most
frequently used words, of more than 100 known definitions of life.
The recent discovery that both genes and genomes appear to have emerged
originally as simple tandem repeats, with subsequent mutations
increasing their complexity makes such definition even
more attractive. One can view a genome as molecular habitat for
emergence of “new life” in the form of expanding and mutating simple
repeats. In that sense, and under the above minimalistic definition,
life never stopped emerging, starting some 4 billion years ago with
replicating RNA, and continuing to this day within the genomes of every living organism.