Post n. 45 English
Etichetta Zna
Darwinism was a revolution in human thinking and
an indescribable boost to scientific research into all that is known about life
and its origins. More than 160 years have passed since the publication of The
Origin of Species, which revolutionised our worldview. During this time,
scientific research has produced an enormous amount of work that has confirmed
the theory in its general outline, but has also made some changes.
The origin of life and microorganisms were not
Darwin's subjects of study, but some of his suggestions anticipated some of the
results that scientific research has achieved over a century later.
Around 1870, in a letter to a friend, Darwin
wrote: "If (and that is a big if) we could imagine that in a small hot
pool, rich in ammonia, phosphoric salts, light, heat, electricity, etc., a
protein compound was chemically formed, ready to go through even more complex
changes [...]". But Darwin's official position was firm and clear: in the
present state of knowledge it is not possible (ultra vires) to formulate a theory of the origin of life.
However, in 1924 A. I. Oparin, who was then Professor of Plant
Biochemistry at Moscow University, translated this idea into a kind of
scientific theory and published it in a book: 'Origin of Life'. According to
Oparin, carbon on our planet was bound to metals in the form of carbides. When
these came into contact with water vapour, they reacted to form hydrocarbons
and then many other organic compounds. When the temperature on the surface of
the earth dropped below 100°C, water began to condense and all these compounds,
contained in the atmosphere, were drawn into a 'primitive boiling ocean' where
they began to react, forming larger and larger molecules.
In 1929, J. B. S. Haldane, without knowing
Oparin's ideas, published a short article on the origin of life. According to
Haldane, the primitive atmosphere did not contain oxygen but probably H2
(hydrogen), H2O (water), NH3 (ammonia), and CH4
(methane) like the atmospheres of Jupiter, Saturn and Uranus. More complex
molecules would have been formed in the atmosphere by solar radiation. These
organic compounds, carried away by the rainfall, would have accumulated in the
primitive ocean where they would have reacted to form complex molecules, giving
rise to a 'dilute hot soup' where the first organisms would have originated.
Darwin's 'small hot puddle' became diluted hot
soup, which was immediately translated into 'primordial soup'. Around 1950,
with H. Urey and S. Miller, using a mixture of gases similar to the one
suggested by Haldane, S. Miller, with the addition of energy (electrical
discharges), succeeded in producing amino acids, which are components of
proteins, and many other organic substances.
Haldane's theory of the formation in the
atmosphere of substances fundamental to the origin of life and their collection
in a 'primordial soup' where life originated seemed to be confirmed.
But, as is amply illustrated in 'Prebiotic
Chemistry and the Origin of Life' New Edition 2019, the formation of protein
compounds is not possible in a primordial soup. And even if someone wants to
substitute the warm depths of the ancient oceanic ridge for the hot pool, the
formation of protein compounds in aqueous environments presents insurmountable
problems.
In conclusion, in the wake of the Darwinian idea
of the small warm pool, the research found that, among the molecules
fundamental to the origin of life, it is very likely that amino acids appeared
first, with the consequent appearance of protein compounds, even if not in a
warm pool.
In concluding "The Origin of Species"
(6th edition) Charles Darwin wrote: "Therefore, on the basis of the principle
of natural selection with differentiation of characters, it does not seem
incredible to me that, from some of these lower and intermediate forms, both
animals and plants may have developed; and if we admit this, we must likewise
admit that all the organisms that have ever lived on earth may have descended
from one primitive form. However, this deduction is essentially based on
analogy, so that it matters little whether it is accepted or not. It is
certainly possible, as G. H. Lewes states, that, in the earliest beginnings of
life, many different forms evolved; but, if so, we may infer that only a very
few have left modified descendants.
However, “one primitive form” proved more
attractive to scientists and was soon translated into LUCA (Last Universal
Common Ancestor), which represented the trunk of a huge number of trees of life
that numerous evolutionists rushed to illustrate.
But with the publication in 1999 of W.F.
Doolittle's lattice tree, the concept of a universal ancestor vanished, making
way, as C. R. Woese puts it, for an aggregation of the universal ancestor. R.
Woese, a common but somewhat flexible aggregation of primitive cells that
evolved as a unit and eventually reached a stage where it broke up into several
distinct communities.
Or, as Darwin suggested '...only a very few have left modified descendants' anticipating, as already pointed out, scientific research by over a century and a half.
Darwin's theory in its essentials, with reference
to the origin of species, is based on three fundamental facts:
1) More
individuals are born than can survive.
2) Individuals
are not all the same but have variations.
3) Natural
selection: the individual with the most suitable variation in a given
environment survives.
This natural selection, according to Darwin,
proceeds slowly and progressively.
Around the middle of the last century, the
discovery of nucleic acids recognised the fundamental role of genes as the
basic control units of the organism. Following these discoveries Darwin's
theory was extended to genetics under the name of Neo-Darwinism, now known as “synthetic
theory”. This theory, extended to all living organisms, states that natural
selection operates on genes and that the variations Darwin refers to are random
mutations that appear continuously in genes and are passed on to descendants.
Like Darwin's theory, the synthetic theory also takes a slow and progressive
view of natural selection.
As G. L. Stebbins and F. J. Ayala report in
"The Evolution of Darwinism" Le Scienze 1985, studies conducted in
the 1970s and 1980s support the hypothesis that the development of variations
in DNA is stimulated by a type of molecular determinism, and not just pure
chance. Furthermore, according to M. Kimura's neutrality theory, chance
controls not only the initial appearance of genetic variations but also their
subsequent establishment in a population. Still within an evolutionary vision,
Telmo Pievani in "Ripensare Darwin?" le Scienze 2015 points out how
some discoveries of the last twenty years have led some evolutionists to
support the need to build an "extended evolutionary synthesis", i.e.
a theory that does not limit itself to explaining evolution only through genes
and selection.
These are arguments that concern insiders that
often provoke heated controversy and that have not yet found a synthesis. In
this article, we are not concerned with these topics or with small populations,
but want to deal only with those macroscopic events in the history of life, now
universally accepted by evolutionists, that are definitely non-Darwinian or
non-neodarwinian.
Around the 1970s and 1980s, four non-Darwinian
events were discovered of which Darwin could not have been aware:
Endosymbiosis, the theory of punctuated
equilibria, lateral transmission, and epigenetics.
Endosymbiosis
Life originated in the form of single-celled
organisms similar to today's bacteria, called prokaryotes. The cells of
prokaryotes consist of a cell membrane, or plasma membrane, which separates the
cell from the external environment. Inside the cell is a fluid, the cytoplasm,
which contains the genetic material, an organelle for protein synthesis
(ribosome), enzymes, and small molecules. The eukaryotic cell, from whose
evolution we also descend, is larger than the prokaryotic cell and its
chromosome is contained in a distinct central nucleus. Eukaryotes differ from
prokaryotes in that they contain organelles in particular the mitochondria,
which produce energy through oxygen and nutrients and in plant cells also the
plastids known as chloroplasts in green plants.
As David Quammen illustrates in “The Tangled Tree”
2020, the hypothesis of an endosymbiotic origin of eukaryotes originated in
1907 by Konstantin Merezkovsky, who suggested that cell organelles such as
mitochondria and chloroplasts were the remnants of bacteria that had been
captured by and evolved from larger bacteria. Merezkovsky was long regarded as
a madman, not least because of his turbulent life, and his idea was branded “an
amusing fantasy”.
For more than half a century this hypothesis was
almost completely forgotten, but in 1967, it was revived by a young and
tenacious researcher, Lynn Margulis, who published an article in the Journal of
Theoretical Biology in which she explained the theory in more detail, including
drawings illustrating the process. In an article published in 1971
"Symbiosis and evolution in “Le
Scienze”, she argued that cells without a nucleus were the first to evolve;
those with a nucleus are not, however, simple mutant descendants of the oldest
type of cell, but the product of a different evolutionary process: a symbiotic
union of several cells without a nucleus. On other occasions, he argued that
neo-Darwinism was wrong about the main source of genetic variation that drives
evolutionary innovation. With a clear reference to Darwin, he added that the
real evolutionary innovation came from symbiosis and that life on earth
followed the path of cooperation and not of struggle for survival.
Despite the fact that at that time it had been
discovered through electron microscopy that mitochondria and chloroplasts
contained DNA, the scientific world of the time considered Margulis to be an
intelligent, stubborn scientist, but in the grip of a crazy idea and even
detested by some. In the decades that followed, Lynn Margulis continued to
publicise her ideas, but it was not until 1992, after the sequencing of their
DNA, that it was confirmed that these organelles were descendants of bacteria
captured in ancient times. Konstantin Merezkovsky and Lynn Margulis had been right;
the eukaryotic cell had originated by endosymbiosis: an Archaea hosted a
bacterial protein that subsequently evolved into a mitochondrion
Punctuated
equilibria.
Natura
non facit saltus; a principle also used by Darwin in the Origin
of Species to emphasise that the evolution of species is slow and gradual.
Since the fossil record did not confirm such an evolution, Darwin concluded
that it was incomplete.
The Modern Synthesis translated this idea by
stating that the changes observed in species were due to small mutations that
gradually accumulated in the genetic makeup.
In 1972 Stephen J. Gould and Niels Eldredge began
to publish the first articles on this problem, summarised in "Gli
equilibri punteggiati" 2008 (Italian edition) by S. J. Gould and
"Rivedere Darwin" by N. Eldredge. As S. J. Gould writes in his essay
"[...] I felt a great discomfort because of the Darwinian conviction that
any evidence that did not fit into a gradualistic sequence should be attributed
to imperfections in the fossil record" and N. Eldredge: "Simple
extrapolation does not exist. I discovered this back in the 1960s, when I tried
in vain to document examples of the kind of slow and steady change that we all
thought must exist, ever since Darwin said that natural selection should leave
just such a detector sign in the fossils we collected in the cliffs. Instead. I
discovered that once species appeared in the fossil record, they no attempted
to change much at all, but remained unflappably and relentlessly resistant to
change, as is natural, often for millions of years.
Ultimately, according to the two researchers, it
was not the fossil record that was incomplete but the theory that was wrong.
There is no slow and gradual evolution. Species appear and in a few millennia
reach their main characteristics, after which they enter a phase of
"stasis" for millions of years, during which there is a slow and
gradual evolution with almost imperceptible variations.
But S. J. Gould added: "The central
proposition of punctuated equilibrium states that the vast majority of species,
as presented to us in the fossil record through the reconstruction of their
anatomical and geographical variation, appear at geological instants
(punctuations) and then remain unchanged (stasis) during their long existence.
[...]. The punctuated equilibrium does not merely assert the existence of a
phenomenon, but dares to make a much stronger assertion, namely that of its
predominance as a macro evolutionary model on a geological scale".
Open up heaven! The orthodox Darwinists, with
Richard Dawkins in the forefront, accused Gould in particular of undermining
Darwin's theory and favouring the arguments of creationists. When dogma and
ideology crystallise ideas. In the twenty years since the publication of the
first article, the theory of punctuated equilibria has given rise to a great
deal of debate. Other data added by numerous researchers have confirmed the
theory, which corrects but does not deny Darwin's theory.
Giovanni Occhipinti
Next article, end January 2022 (Where do we stand with Darwin, 2nd part)
Nessun commento:
Posta un commento