Re: Essay: What is Life?

> In my own area of interest, OOL, one encounters a variety of answers
> to the question "What is life?" that seem to be based on what life
> DOES.
> 1. Life dissipates energy - it is a thermodynamic open system far
> from equilibrium.
> 2. Life propagates information - it is characterized by genetic
> replication.
> 3. Life evolves - it is characterized by heritable variation in fitness,
> i.e. by natural selection.
> 4. Life reproduces - it is characterized by the potential for
> exponential growth in population sizes.
> 5. Life maintains itself - it is autopoietic.
> 6. Life grows; increases biomass - it is characterized by an
> autocatalytic metabolism.
> Plus two more that don't quite fit the "What it does" framework.
> 7. Life is cellular - "Every cell from a cell" but entities smaller
> than a cell are not "alive".
> 8. Life is not spontaneously generated - "All life from life".
>

RKS:
I didn't make any claims about life actually having a purpose, just raised
the question of using that approach. One can use the same approach for any
of the processes associated with life. For instance, is genetic
transmission a means of achieving something, or the end in itself. If it is
the end in itself then we would only count DNA and RNA in any discussion of
the transmission of information between generations. If it is only a means
to an end, say the purpose is to transmits information, then we may
postulate that there are other methods, even if only in principle, of
transmitting 'information'.

Given that the purpose is to transmit information between generations we can
also count methylation, microtubules, and so on that are known to transmit
some information between generations, under the same umbrella term, of which
genetic transmission is only one example among others. Such a position has
no trouble incorporating the prions and the information they can potentially
convey into the same overarching concept of information transmission.
Concepts such as cultural transmission of information may also impact on the
phenotypic development of a species, though humans are subject to this to a
far greater degree than any other animal.

Your '7' is problematic in that you define life according to the structure.
This is a counter position to the one I am suggesting. By asking "What is
life?" we can come up with a definition free of current examples (such as
cells) of which the current examples and others undreamt of are summed under
the same definition. Biologists have arbitrarily decided that life should
be defined by certain examples bracketed by the cell on the small scale and
skin on the larger scale. These constraints are arbitrary - they are not
defined by a definition of life of which cell and organism are examples.
Any definition of life independent of examples may well incorporate such
non-skinned entities such as colonies, slime mould conglomerates and biotas.

Your '8' introduces a much bigger problem than it solves (spontaneous
generation of the 19th century). If life only comes from life then life
must have been introduced to the Earth. Even with this thought in mind,
life must have existed, by your assertion that life only comes from life,
eternally.

I disagree with your '3' - evolution is the result of adaptation. If a
species is adapted to an environment, and the environment is stable, then
that species does not evolve. Thus the assertion that 'life (arbitrarily)
evolves' is wrong.

Your '4' does not cover single celled animals, which are the most common and
possibly oldest forms of life. Prokaryotes and archaea do not reproduce -
cells divide. Cell division is not considered to be reproduction in any
biology text book that I am aware of.

Not all life maintains itself (5). Most extant life has successfully
maintained itself or is in the process of becoming extinct. Earliest forms
may not have had a successful maintenance capacity and so many forms may
have become extinct. The fossil record seems to confirm that extinction is
a very common phenomena. I can only imagine that you are refering to
'successful forms of life' ie those that have survived to the present time.

Kind Regards
Robert Karl Stonjek


.

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