Newsgroup: it.politica
Titolo: (OT) Articolo di TheScientist.com richiesto da XO5 (lungo e in inglese)

Even as political rhetoric and court battles reflect a public struggle
over Darwin's theory of evolution as an explanation for the origin of
humans, a different struggle is unfolding within science about the
adequacy of evolution as a theoretical foundation for biology. On the
surface, the two debates seem to have little to do with one another,
but in a subtle way both reflect the need for a richer theoretical
biology. The perception of evolution among the wider public might even
be improved by better communication of scientific concerns about the
limitations of evolutionary theory, and how those concerns are being
addressed. 
A sympathetic reading of public distrust over evolution would be that
a simple theory of change seems too bare to account for the richness
of structure we see in the world around us, and for how that structure
first came to form. This certainly indicates a failure to appreciate
the complex origins of order, and most popular science writing on
evolution has been devoted to explaining the surprising and delightful
origins of eyes, wings, or peacock's tails. But besides this, an
intuitive discomfort that a theory of change cannot adequately account
for genuine novelty has a scientific counterpart. The original
emergence of life from a lifeless geosphere is one of the most
striking such cases. 
 
While they share a certain level of unease, the public and scientific
debates diverge sharply on how to overcome the limitations of
evolutionary theory. Public rejections of Darwinian ideas are bound up
with a wish to introduce something more complicated than undirected
variation and brute selection: a creator or designer responsible for
novelty and innovation. In science, we recognize that while
evolutionary theory is limited, some of the limits concern its
connection to simpler - not more complicated - scientific principles
than those introduced by Darwin. The remarkable story that is emerging
about the origin of life is that these simpler principles may account
for aspects of the biosphere that are older even than the evolutionary
era itself, and which tie life at its core to the geochemistry of the
earth. 
Evolution as Biology's Unifying Theory
To understand the role and also the limitations of evolutionary
thinking in biology, it is helpful to recall a little history. Biology
as a unified science did not even exist until well into the 20th
century. Before that time, only application domains were recognized:
systematics, botany, morphology, ecology, paleontology, physiology,
medicine, and so forth. Each of these fields had its own
domain-specific knowledge and even some elements of theory. However,
the possibility of an overarching theory for all of life was not
central to any of them. When this situation changed, the change was
not a result of new ideas, but rather of ideas that had already been
current for nearly a century, and had gone unrecognized as a
foundation for theoretical unity. 
If public discontent with evolution stems from an intuitive
appreciation of its limits, perhaps we as scientist can accomplish
more by discussing these limits scientifically. The two ideas that we
now think of together as the "theory of evolution" were Gregor
Mendel's conception of the gene, and Charles Darwin's model of natural
selection. Mendel had argued 1 in 1865 that traits do not mix like
paint when they are handed down from parents to offspring, but rather
are shuffled like cards. The concept of the unmixable source of a
trait (say, whether peas would be smooth or wrinkled) was given the
name gene, and Mendel's important observation was that the particular
forms of genes usually did not change as they were passed from parents
to offspring. This kind of faithful inheritance of traits, and
shuffling instead of mixing of genes, allows populations to preserve
diversity, instead of washing all traits out to some average form. 
Darwin contemporaneously (1859)  had argued that the infrequent
variations that do occur as traits are passed from parent to offspring
need not be directed in order to enable adaptation. The greater
reproductive success of individuals with better-adapted traits would
be sufficient to establish the favorable forms. Darwin called this
process natural selection as a reference to the selection exercised
deliberately by human breeders, and he recognized that variation is
necessary to give either breeders or nature the raw material from
which to create changes in form. 
The memory of life works so spectacularly well that it is often
forgotten in biology just how difficult it is to produce a material
that can remember anything, let alone remember it for billions of
years. Mendel's heredity and Darwin's selection were not theoretically
central to the many particular life sciences, and were not even linked
to each other until they were brought together by several researchers
in the 1930s and 1940s, into what Julian Huxley called the Modern
Synthesis of evolutionary biology.  The key observation of the Modern
Synthesis (as it is now known) was that Mendelian heredity preserves
the diversity of forms available in a population, while Darwinian
selection changes their frequency of occurrence. Together the ideas
link variation on the short-term to change in average properties on
the long term. This synthesis did not replace the domain-specific
theory in many life sciences, and in many cases it did not
significantly change how it was used. The Modern Synthesis proposed a
way in which random variations, with no foresight, could
systematically lead to population changes in a manner that made sense
in each of these fields. 
This theory of evolution is really a framework for thinking about
change in the living world. It provides no specific guesses for the
kinds of traits that may exist, no strong requirements or prohibitions
on how they may interact to make a complex organism or ecosystem, and
no commitments to how innovation can occur. Even the problem of how a
differentiated population ultimately divides into two distinct species
(posed in the title of Darwin's seminal work)  remains a major
technical problem in evolutionary biology. 
There is no reason to view Mendel's and Darwin's ideas as
self-contained or complete for biology, in the sense that all needed
principles of organization can be generated from these two ideas
alone. What they provide is a new class of dynamics that is different
from what had previously been considered in physics, chemistry, or
engineering. While these ideas seem particularly suited to answering
questions about life, they have also found their way into thinking
about such diverse fields as economics and Internet security, so they
are certainly not uniquely biological. 
Evolution's Requirements
Darwin's ideas were controversial as soon as they were introduced,
because he and his contemporaries appreciated (and he intended) that
they separated the concept of "good design" (called adaptation in
evolution) from a need for a designer. In the enthusiasm for this one
point, many other equally important points about the principles of
evolution have been glossed over, and their omission is starting to be
felt in practical problems in biology. Both Darwin and Mendel, working
more than 150 years ago, took as self-evident what constituted an
individual organism, and with a little more care, which similar
organisms constituted a species. They recognized that individuals
reproduced similar types of individuals, apart from minor changes, and
that birth and death of individuals marked the change of generations. 
Carbon fixation is one of the most conserved reactions throughout the
biosphere.Today, as we consider more life forms and their
interactions, and especially as we consider the origin of life from a
lifeless geosphere, the situation is more complicated. When multiple
strains of virus "mate" by coinfecting a host, many different notions
of individual become blurred even within a single infected cell: the
two viral strains that might insert genes into the host genome; the
viral and host genomes that are both struggling to control the same
cell's metabolism; and the host cell's participation in a larger
organism. We have learned that quite distinct strains of bacteria and
archaea routinely exchange genes, and they probably did so much more
promiscuously in the earliest stages of cellular life than they do
today. Thus, the genetic and metabolic notions of individuality become
even more loosely bound, and the concept of species becomes extremely
problematic. These examples, and many others as well, illustrate that
the concepts that Mendel and Darwin took as the starting points for
their science may not apply to all biological situations. Indeed, even
when they do apply, they must be explained within the context of a
larger science. 
We can identify four assumptions that must be made for evolutionary
ideas to be even expressible, and we can then ask what science must be
done to justify these assumptions, in particular for the first
emergence of life. 
1. Contingency
Traditionally in physics and chemistry, preparing an experiment in the
same way twice was expected to lead to the same outcome, as a
criterion for asking well-posed questions. A feature that makes
biology a fundamentally new science is that "replaying the tape" of
life would, in many important respects, not lead to the animals and
plants we see in the world today. 4 If the nature of life did not
permit such variation, it would not have been possible for Mendel's
peas to take either smooth or wrinkled forms, while remaining parts of
viable pea plants. The fact that smooth or wrinkled variants could be
passed down through heredity, without quickly reverting to a single
form, meant that the form of each new generation was contingent on the
form of its parents; that is, random variations in the past
potentially could be preserved in populations for long stretches of
time. Evolution can occur only when variations can arise and be
preserved in this way. 
2. Memory
Of course, heredity requires not only the possibility for variants to
persist; it also requires a way that the features of the parent can be
remembered and passed down, and this is the role of DNA and RNA, the
carriers of Mendel's genetic information. The memory of life works so
spectacularly well that it is often forgotten in biology just how
difficult it is to produce a material that can remember anything, let
alone remember it for billions of years as life has remembered many
details of cellular structure and function. Yet the material of cells
is not different from the material of the nonliving world except in
its arrangement, and it is well understood in physics that
arrangements constantly decay due to thermal jittering and other
shocks. Some of the most sophisticated ideas in the field of
condensed-matter physics concern the making of materials such as
magnets, whose order is self-reinforcing over long times, allowing
them to form memory devices. 
3. Control
Memory alone is not enough for evolution to occur. Unless different
genomes could reliably create different kinds of organisms and ways of
life, the remembered variations could not be submitted to natural
selection for comparison and judgment. But any controller, including a
genome, must first have autonomy from the thing controlled (the
definition of control is that instructions mostly flow in one
direction), leaving the controller somewhat detached from feedback
about the consequences of its actions. When the components of the
controller themselves fluctuate, wear out, or fail, it becomes capable
of unfettered mistakes, and all human-designed control systems
ultimately rely on intervention from the human world to repair and
re-align them. Yet within life, control mechanisms have not only
spontaneously emerged; they are self-sustaining within the enclosed
system of the biosphere. 
4. Individuality
The reason it is possible for Mendelian heredity to preserve
variation, and for Darwinian selection to act on it, is that traits do
not mix continuously like colors of paint. At the same time, traits
are not inherited independently. The many variable features of an
organism are reproduced as a package if the organism successfully
reproduces, and they are lost as a package when it dies. The granular
nature of both traits and the individuals in which they are aggregated
make selection a very complex mathematical process. Moreover, as we
saw above, many different ways of collecting traits together in
individuals exist, each with different dynamics. Yet at the same time,
new forms of individuality are rare, suggesting that there are stark
limits to how traits may be bound together in an organism while
preserving in it the ability to evolve.  
In physics and chemistry, none of these four features is a common
occurrence, and yet evolution presupposes all of them. If life began
in a physical world where none of them was present, we must first
understand how and why they came into existence, before we can apply
evolutionary ideas to study their subsequent change and refinement.
Some modern studies of the origin of life 6 are addressing these older
problems of emergence and looking for mechanisms that were predominant
before Mendelian/Darwinian evolution was possible. The possibility
that these mechanisms were simpler than evolutionary mechanisms also
suggests that they are more robust, and that the order they initiated
may still be observable in the organization of the biosphere today. 
New Views of Order in the Biosphere
How does such a change in theoretical perspective lead us to reexamine
the order in the biosphere? For one thing, if we do not assume the
primacy of individuals, we notice that the strongest regularities of
modern life cannot be seen in individual traits, but only at an
ecological level of organization. 6 Here we find a common set of
reactions for the synthesis of biological molecules that is universal
throughout the biosphere and across the whole history of life. The
stability and invariance of metabolic pathways gives them the
appearance of features of the geosphere rather than of anything that
depends on memory or control by individuals. 
One of the most primitive functions life must perform lies at the very
core of metabolism: It is the capture of carbon from environmental
carbon dioxide (CO 2), which was abundant in the prebiotic era, and
its synthesis into the backbones from which the rest of biomolecules
are made. An amazing, small cycle of only 11 simple molecules, known
as the reductive citric acid cycle, is capable of performing this
feat. Some version of the reactions in this cycle is the foundation
for biosynthesis in every kind of ecosystem on earth. 
 
 2001The cycle's basic function is to access otherwise inert CO 2,
combine the carbon with electrons, and make molecules capable of
repeating this reaction. The reaction sequence has the remarkable
property that any molecule in the cycle, by accreting CO 2 to become
longer and then splitting into two, reproduces a second copy of the
same molecule while returning the first copy. Thus, like compound
interest, it grows and draws diffuse carbon into a very specific
pathway. The mathematics of energy and carbon that flow through this
cycle resembles the mathematics that drive a hurricane to become the
major transporter of moisture and energy over the oceans where it
forms. 
Carbon fixation is one of the most conserved reactions throughout the
biosphere. It suggests that a bridge between geochemistry and life may
be found in the mechanisms of metabolism and the principles of
ecology, not in compartments or memory molecules, which could have
come later. A metabolic organization capable of serving as such a
bridge, however, could not have come from just any old network of
organic chemical reactions. It would need to have been: 1) sparse
within the network of possible reactions so that a few molecules were
created in large supply, rather than a huge diversity of one-off
molecules arising happenstance (which could not be assembled into
anything); 2) particular, in that the pathways observed should be
necessary and predictable, rather than accidents (which would depend
on later memory mechanisms to be preserved), and 3) robust under
jittering of the components, to permit later molecular memory systems
to emerge using them as foundations. These principles can be used to
find other primal reactions. 
If the biosphere emerged through the self-organization of a metabolic
system, like the citric acid cycle, the later formation of individuals
would be understandable as solving a different problem of packaging.
Distinct species can make up an ecosystem by partitioning metabolic
tasks to become complementary specialists, but only if they solve the
complex problems of obtaining the resources they do not make and
settling into a balanced flow of resources among all the members of
the ecosystem. 
This view of the origins of life changes our understanding of the
biosphere today in two ways. First, ecological principles become the
foundations for the rest of biology, rather than merely secondary
consequences of relations among individuals. Second, we should be
warned that when we act as engineers in the living world, imagining
that we can manipulate properties of individuals but remain ignorant
of principles of ecology, we should expect the biosphere's response to
be complex and not necessarily in accordance with our designs. The
rapidly rising cost of industrial agriculture, and its fragility to
shocks in energy supply, to pests, and to weather, is directly tied to
the loss of natural ecological sources of stability in industrially
managed agricultural systems. 
When we consider what would be required for metabolism to have
self-organized without supervision, we realize there is a rich,
hierarchical, modular structure of the extant metabolism of the
biosphere that looks far from accidental. The functions that
particular chemicals fulfill, in the context of both the network and
the constraints of the geochemical environment, suggest that the
presence of these chemicals as a foundation for life may be required
from first principles. 
Many of the biological amino acids have simple and perhaps inevitable
synthetic pathways starting from citric acid cycle backbones.
Phosphorus, the element responsible for the assembly of large
biomolecules by polymerization of small ones, naturally leads through
a range of intermediate-sized compounds (technically termed cofactors,
but we know many of them as the vitamins), which are central to
molecular assembly and catalysis throughout metabolism. Even the
genetic code, a master instruction set for the translation of RNA
memory into protein control, has regularities that may be of
precellular chemical origin. 
Perhaps the most important feature of a chemical logic for metabolism
on the early earth is that such a logic would not have become
irrelevant when memory and control arose. More likely, it determined
easy paths for biosynthesis, and gave fitness advantages to organisms
that used them, over organisms that attempted to deviate too strongly.
Thus we should not be surprised that modern life continues to respect
an organization that first came about in the geosphere6. 
The observations turned up in this way of asking about origins are
ordinary enough, but they suggest a conceptual framework for biology
that extends well beyond the classical theory of evolution, not only
for the origin of life, but for its organization at all times. By
drawing inputs from the many theoretical sciences that bear on the
transition from lifeless to living matter, and in the process
embedding biology more thoroughly in the framework of the other
natural sciences, we learn that the required other origins of order
may be simpler than the Darwinian paradigm, not more complex. 
If public discontent with classical evolution as an inclusive theory
stems partly from an intuitive appreciation of its limits, perhaps we
as scientists can accomplish more by discussing how these limits are
considered scientifically than by downplaying them. 
Eric Smith is a professor at the Santa Fe Institute.

 humans........
Potrà anche essere interessante, ma non ti pare di esagerare con
questi lenzuoli di copia e incolla.
Chi vuoi che li legga?
vdm

 humans,
Senti, a guardare come ragioni te, viene il dubbio che tu discenda da
una tellina.
Piantala di rompere le balle, sei completamente Off-Topic.
P

Chi vuoi che li legga?
Chi me lo ha richiesto, direi.

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Infatti c'ho messo il tag, you stupid wop.