>During a discussion about primitive forms of life, someone popped the ques-
>tion why there is so little biochemical variation around. His argument ran
>that most life on Earth has some form of DNA or RNA inside it, and that there
>is little evidence for anything more primitive. He then proceeded to say that
>regular biological evolution breaks down at the biochemical level, and that 
>you would need a different theory (but not any form of creationism, he was 
>quite emphatic about that) in order to explain all sorts of basic biological
>structures, like for example DNA.
>
>My first reaction was to dismiss the idea entirely, despite the fact I am
>not a biochemist. Nevertheless, I decided to hunt around if I could find some
>information on this particular subject. But most hits Google turns up 
>(including those of the much more limited scholar's edition) are poisoned 
>with creationism, and the library at my university does not have the
>necessary
>literature for a biochemical search.
>
>Is there any truth to what this person claims? Any links to informative 
>articles would be most appreciated. (I vaguely recall that a recent edition
>of the New Scientist featured an article about a quantummechanical spark of
>sorts to begin it all, but I don't have the print edition at hand. Something
>like that.)
>
>
>Kind regards,
>Maarten
>

First, it is not easy to prove that there is little biochemical evolution
around. On the contrary, Kirschner and Gerhart (Evolvability, Proc. Natl.Acad
Sci. USA, vol. 95, pp.8420 - 8427, 1998) argue that during ~3 billion years of
life on Earth unicellulars went through considerable evolution, but have
accomplished only modest morphological evolution.

However, in relation to multicellulars, his claim, is not baseless: during half
a billion years since it emerged, the multicellular life has recorded a
phenomenal and amazing morphological evolution, while their biochemical
evolution has been, at  best, modest.

At first sight this is paradoxical: where biochemical evolution has been rapid
the morphological evolution was slow (unicellulars); the reverse is observed in
multicellulars: without much biochemical evolution they underwent an ultrarapid
evolution. 

But, paradoxes normally are illusions deriving from insufficient knowledge or
wrong conceptions. In our case the source is an unjustified extrapolation of
the mechanism of the evolution of unicellulars (which is based almost totally
in selection of genes and genic mutations) for explaining evolution of
multicellulars.

Let's elaborate:
even if we would ignore the early forms of unicellular life, which is believed
to have had a much smaller number of genes in their genome, modern mycoplasma
cells have ~470 genes. Higher in the ladder of evolution of unicellular
procaryotes, E. coli contains ~4000 genes and still higher in eukaryote
unicellulars ~9000. There is a clear and unambiguous causal relationship
between genes and the evolution of unicellular life.

The situation in multicellulars is quite different: no relation is observed
between genes and the evolution of multicellular life. Look, there is a
consensus that we humans are, at least, a little more complex than one of the
most simple worms, Cenorhabditis elegans, which contains only 900 neurons
(compare it with  one trillion in our brain), and yet we have a comparable
number of genes with that worm and less genes than a mice, while the genome of
the lungfish, Protopterus aethiopicus has 20 times more DNA than our genome.

Now to summarize: the evolution of unicellulars is clearly related to the
evolution of their genes via the natural selection of genic mutations, whereas
evolution of multicellulars may depend on anything but genes. The reductionist
approach to the biological phenomena in the second half of the 20th century, in
an atmosphere of enthusiasm promoted by epoch-making discoveries of molecular
biology and genetics, would wipe off that essential difference in the mechanism
of evolution between the multicellulars and unicellulars and identify evolution
of living beings as not much more than evolution of their genes (in its extreme
irrational form, it would consider the evolution of living systems just a means
of gene survival and propagation). The genetic mechanism of evolution of
unicellulars, contrary to all the available evidence, was extrapolated to be
used as an explanans for evolution of multicellulars. 

For every error a price  has to be paid somehow. In an expression of the modern
American diplomacy: you break it, yuou own it. The reductionist view and
approach to the evolution of life has contributed to the modern wave of the
extrascientific and pseudoscientific attacks against the evolutionary thought.

Thank you,
 
Nelson R. Cabej
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