Biology is the science of living things, therefore the definition of life is a matter outside biology.
the definition of life is, properly speaking, outside of science;
despite that the mainstream current definition is derived from chemistry
- based on the replication of molecules with the possibility for
variation and selection. But that this really constitutes 'life', does
not come from science but is a non-scientific assertion or assumption.
other mainstream definition of life refers 'metabolism' - but the
'real' nature of life is just a matter of choosing a definition - there
is no right answer; and furthermore replication and metabolism may have
evolved separately and using different molecular types.
example, Freeman Dyson has argued that metabolic life may have evolved
firstly among proteins, and this metabolism was parasitised by
replicating RNA molecules - and later protein and nucleic acids
co-evolved to join in that symbiosis we observe as 'the cell'.)
selection must have something to work on - and that something must be
sufficiently stable to allow for some reasonably large number of
generations to do the work of natural selection.
deeper, metaphysical sense; natural selection presupposes an
understanding and identification of 'form'; because form dictates what
it is that evolves, and when that form stays the same or when it changes
to another and different form. Unless form, its constancy and change
are already known, in a definition originating outwith biology, then the
workings of natural selection could never be observed.)
life must have been initiated by chance; then this spontaneous life
must have 'fallen-into' some natural form, pre-existent order,
stereotypical pattern, auto-catalytic system, or 'strange attractor'
which kept it going for a while - because only then could natural
selection do its work.
Even with natural forms - when
it comes to life: what chance has given, chance also can take away. And
any form of life will have a tendency towards extinction from what has
been termed 'error catastrophe' (unless it has evolved methods for
Error catastrophe is what happens in a
metabolising or replicating system due to the spontaneous occurrence of
errors to processes and copying. Such errors will naturally accumulate
over time, unless there is some means to prevent them accumulating.
(Mutation accumulation is a special type of error catastrophe:
the vast majority of errors will damage functionality (because only a
tiny proportion of undirected changes will improve functionality), and
each new accumulating error will tend further to damage functioning -
tending towards a catastrophic loss of function with death of the
individual and/or extinction of the lineage.
however life is defined, the principles apply that life must form and
have some degree of stability by some combination of chance and natural
forms; and then the first job of natural selection is to stabilise life.
Put it another way - life may form spontaneously - but it will not last without the help of natural selection.
selection must primarily be about sustaining life, because only when
life is being sustained, is there a possibility of the of life being
Because it is statistically improbable for an
error to be an improvement; and therefore it typically requires
considerable time (in terms of generations), and or a considerable
population (because numbers amplify the number of generations) before
the undirected ('random') occurrence of a beneficial error.
life happens by chance but life is also is doomed by chance to be
short-lasting; therefore the first 'job' of natural selection is to keep
life going just as it is - just as it has arisen by chance.
And only after
life has evolved such as to have been kept going just as it is by
chance, is there any possibility of natural selection to produce
adaptation of organisms.
Natural selection and the origins of life: First sustaining, then later (perhaps) improvement.