Re: Essay: A first draft of a definition of life

Definition or not, my model can identify life unambiguously.
Joe:
I have to disagree. LUCA is the most recent common ancestor (if there
was only one). But that is entirely different from saying that it was
the first living form. There is nothing about being "life" that would
require that the immediate ancestors of LUCA weren't alive. They
could have all the same machinery, and be virtually identical to
LUCA. The first life, however you define it, would be much earlier
than LUCA. LUCA is the last (common ancestor), not the first (of
anything). It is worth thinking about what LUCA looked like, because
we can use existing forms to infer things about it, not because there
is any reason to believe that previous ancestors didn't have genes.
reproduce, metabolize, etc.

It is like saying that the last common ancestor of modern elephants
must therefore be the first elephant,
and whatever went before is then by definition not an elephant.

----
Joe Felsenstein joe (at) removethispart.gs.washington.edu
Department of Genome Sciences and Department of Biology,
University of Washington, Box 355065, Seattle, WA 98195-5065 USA


RKS:
It is impossible to define a thing if the variables include:
A) an unknown list of objects to be covered by the definition;
B) an unknown list of properties to be included in the definition.

There are two main approaches to defining anything, including such tricky
ones as life and, for instance, consciousness:
1) I can examine a list of examples and determine what properties they have
in common or
2) I can examine a list of properties and find examples that satisfy that
list.

For every property defined, the list of objects that fits the list of
properties changes. For every change in the items included in the list of
examples, the list of properties changes.

Do you notice that with the two variables I have mentioned it is impossible
to arrive at a definition because A changes B and B changes A??

The ONLY solution is to introduce some arbitrary cut-off point, either in
the list of properties or in the list of objects to be defined. A
compromise is to split the word to be defined so that one half is defined by
a list of examples and the other half is defined by a list of properties.

That is a solution that will work in principle. The current approach can
not work even in principle (as I have outlined above).

Thus I have broken the word 'Life' into two. Basically, all species that
have DNA and at least one common ancestor can be defined as living if they
are not dead (suspension of animation with no prospect of reanimation).

For the other half we have 'proto-life' which is defined by its properties,
not by its examples. Thus from the definition of life we can list
properties, and from the list of properties we can discover proto-life forms
including those forms that a non-arbitrary cut-off point would include as
life. The compromise is that proto-life forms can live independently for
*some* interval (not necessarily for their entire existence) and life
forms have *some* dependence on others.

There are two choices left for us, and only two:
we can choose to continue as is, knowing that a definition of life is
impossible in principle or we can choose to split the definition, introduce
an arbitrary fixed point, and proceed to define life and then associated
phenomena definitively.

Which solution will better serve the advancement of science?

Kind Regards
Robert Karl Stonjek


.

Relevant Pages

  • Re: Essay: A first draft of a definition of life
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