And what I am trying to explain is that this claim is incorrect. A genetic
code is simply one part of an overall metabolic system; it is not _a priori_
a requirement for "life" in the biochemical sense, though it is a result of
life.
>
>The use of an esoteric definition of abiogenesis to proclaim
>it fact is a little misleading.
>
It is not an "esoteric" definition just because it involves biochemical
terms and concepts you are not familiar with. It is a specific, testable
definition that has been proven to be true over and over again in many
different kinds of laboratory experiments. It is misleading only to those
who believe in a vitalistic type of life, or like you try to load life with
requirements that in fact did not appear until after life itself appeared.
In other words, a genetic code is an _a posteriori_ requirement; once we
have life we should get a genetic code, but genetic code itself is not
required in order to get life.
>
>>Let me ask you a question: are red blood cells alive by your
>>definition?
>
>By themselves, no.
>
Then your definition is wrong, because by any biochemical or biological
standard you wish to use RBCs are in fact alive, in the sense that they do
what living things are expected to do.
>
>They are part of a living system. If isolated, with all
>the things necessary to keep them alive, you will soon lose all of them to
>natural causes with no new little replacement cells.
>
Are you switching gears here? Going from a genetic code to reproduction as
your definition of life? Yes, among modern organisms a genetic code is
needed for reproduction, but in fact the presence of a genetic code does not
guarantee reproduction, either in cells or in whole organisms. If you are
introducing reproduction as a new or alternative requirement for life, it is
irrelevant. It is possible to take an otherwise normal cell with a nucleus
and prevent mitosis from occurring. The cell will thus remain in interphase
forever, despite the presence of its genetic code. Such cells, like RBCs,
eventually die, but until they do they, like RBCs, do everything that a
normal interphase cell is capable of doing. No biologist or biochemist
would say that such cells are not alive simply because they cannot
reproduce. Life involves more than simply reproduction; thus the loss of
the ability to reproduce does not mean the loss of the status of a living
organism.
Besides, your above statement could easily be applied to metazoan organisms
as well. Is a mouse that is isolated form all other mice, with all the
things necessary to keep it alive, not alive simply because it will
eventually die without ever having had the ability to reproduce?
>
>They cannot reproduce.
>
Then it is official; you are introducing reproduction as a new/alternative
requirement for life. It is still irrelevant. Metabolically RBCs are no
different from any interphase cell. If a cell stuck in interphase is
biochemically alive, despite the inability to reproduce, so is an RBC. Are
you suggesting that a mule is not alive because it is not capable of
reproduction?
>
>They do not evolve.
>
Another new/alternative irrelevant requirement? The working definition of
life accepted by biologists/biochemists does not even mention evolution as a
requirement for life. However, like reproduction, evolution is a
consequence of life once it finally appears.
>
>Being part of a living system does not make it alive.
>
No, of course not, but isolated RBCs do not immediately die. They continue
to live until their proteins wear out, at which point their metabolism
collapses. Isolated cells that are permanently locked in interphase live
longer because they can make more proteins, but eventually they also die
when a preprogrammed apoptotic mechanism is triggered. Yet they too are
alive until that event. Both RBCs and interphase cells contain their own
"living system" that keeps them alive until either that system wears out or
is deliberately destroyed. Metazoan organisms are the same way. If they do
not reproduce, if they do not evolve, are they therefore not alive?
>
>>
>>Let me ask you another question: are viruses alive? They have a genetic
>>code, but no metabolic system.
>
>I don't know. I've wondered this for a long time, especially since one of
>my main interests and the direction I've wanted to go in was virology.
>
There is alot of controversy over this, but in fact your definition would
confuse the issue even more. Viruses contain a genetic code, but no
metabolic system, so technically could not be alive, yet they can reproduce
and evolve, and they can make use of a foreign metabolic system, so
technically they should be alive. Using a definition of life that
concentrates on metabolism, however, renders viruses not alive, period. In
fact, I believe that the best current theory about them is that they
represent an evolutionary deadend, an organism that did not arise until
after the appearance of the genetic code in cells, but which tried to
produce a new type of "abiotic organism" (one that didn't need an integrated
metabolic system to reproduce or evolve) that ultimately failed.
>
>The problem, however, with both of these examples is that they are both
>post 'genetic code'. They wouldn't exist without it.
>
Irrelevant. We are testing a definition of life that makes reproduction a
requirement for life. Such a definition states that RBCs are not alive
because they cannot reproduce. As such, interphase cells, isolated mice and
mules cannot be alive either because they too cannot reproduce. This
definition is too restrictive, and the only way to save it is to use
different standards for different circumstances, such as the presence or
absence of a genetic code. However, this means that we do not have one
general definition, but lots of specific, even ad hoc, definitions unique to
each set of circumstances, which is too cumbersome. So a definition of life
that requires reproduction is inappropriate as a scientific or a
philosophical definition, because it produces too many false positives and
false negatives.
>
>You and I would both agree that metabolic systems are absolutely essential
>for life (in the case of viruses, they don't have their own, but they use
>others). I believe a genetic code is absolutely essential for life. Both
>must exist, in my opinion, to define something as life.
>
There were several ways I could answer that, like pointing out that a
genetic code is not the same thing as reproduction, or explaining how the
requirement for both produces false positives (claiming something is alive
because it has both a genetic code and a metabolic system when in fact it
clearly is not alive by any objective standard) and false negatives
(claiming something is not alive because it either does not have a genetic
code or a metabolic system when in fact it clearly is alive by any objective
standard). Instead I decided to address your logic.
You are in fact committing a logical fallacy known as composition (what is
true of the parts of a whole must be true of the whole itself). It is
certainly true that modern living organisms require a genetic code to
produce some of the biomolecules they need to keep their metabolic systems
going (though an organism without a genetic code would continue to live
until parts of its metabolic system began to wear out), but that does not
mean that this must be true for life as a whole. In fact, modern
abiogenetic research has shown that you can get structures that are
metabolically alive and can even reproduce themselves, but have no genetic
code at all. As such, if a definition for life must be based on the most
basic characteristic that is true both for all the parts of life as well as
for the whole of life itself, this definition must be based on
biomolecules/metabolic systems only and not include a genetic code. Our
best research so far indicates that a specific genetic code came late, long
after "life" itself had appeared.
>
>Can the metabolic systems you speak of evolve? If so, is there a ceiling
>to their level of complexity?
>
They can abiotically, but we cannot say how far this might go because on
earth (so far our only known example of life) a genetic code did eventually
arise to provide a faster means of evolution than abiotic evolution. On
another planet, where no genetic code ever arose, who can say?
Kevin L. O'Brien