>Alexei,Actually my claim is that only cells do duplicate autonomously.
>Because it is generally agreed that all extant organisms and cells are
>the descendants of a single cell, my claim is that only this single cell
>started duplicating autonomously and still does
Ok, I see your point. I agree that cells self-reproduce. But I insist
that self-reproduction occurs at other levels as well (organisms,
genes, species). If I can build a model in which I see exponential
(auto-catalytic) growth, then I deal with a self-reproducing system.
The model of Leslie shows the exponential increase in the number
of organisms in a population. Hence, organisms self-reproduce. This
model is very crude, it does not consider any internal structures
or genetic variability in organisms. But it shows self-reproduction
at this crude level. Then I take the model of Fisher (1930) that
describes changes in gene frequency and I notice that some mutant
gene increase in numbers exponentially. Again I conclude that this
is self-reproduction. This model is again very crude (as all
good working models); it ignores mechanisms of gene interpretation
but it captures identity of genes and shows there self-reproduction.
You may argue that these models are phenomenological, they do
not describe details of biochemical processes in cells. My
reply is that all models are phenomenological, some capture
more details, some less, but none of them captures everything.
The more detail you consider in the model the less are chances
that you will detect self-reproduction because there will be
more differences between parents and their offspring. Thus,
too many details is as bad as too little details. There is
an optimum level of details in modeling.
>I don't see how molecules, species or the biosphere can be
>self-replicating.
Example of self-replicating molecule is any autocatalytic
reaction. Crystal growth + mechanical disturbance that break
crystals is such a system. It is well described by A. G. Cairns-Smith
in his book "Genetic takeover" 1982.
A species (population) can be viewed as a super-organism.
Each single organism is like a sensor for the species;
its survival or death indicates the quality of environment.
By sexual exchange of genes, the population integrates information
from various organisms and creates new organisms. Speciation is
a self-reproduction of species. Although gaughter
species differ from the parent species, they have many
common features. Each genera has its identity (often more
striking than the identity of species).
Finally, the biosphere may be self-reproducing by emitting
living organisms to the oter space. For example, when big
comets hit the Earth, then large portions of oceans could
splash out, become frozen, and travel within solar system
and beyond. This ise may contain bacterial spores. It is
quite possible that Earth was contaminated with life from outer
space. Biosphere propagules carry a lot of information about
the parent biosphere. May be in the future hunams will discover
very unusual biospheres that have a different origin compared
with earth biosphere.
Another mechanism of biosphere propagation is by humans.
Humans can be viewed as analogs of generative cells in
the organism.
-Alexei
-------------------------------------------------
Alexei Sharov Research Scientist
Dept. of Entomology, Virginia Tech, Blacksburg, VA 24061
Tel. (540) 231-7316; FAX (540) 231-9131; e-mail sharov@vt.edu
Home page: http://www.gypsymoth.ento.vt.edu/~sharov/alexei.html