Origins 14(1):7-20 (1987).
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IN A FEW WORDS |
The author reviews some of the classical argumentation regarding the spontaneous origin of life and evaluates some of the newer concepts.
Among numerous ideas in currency four or five thousand years ago
about the origin of life was one that is still held dearly by millions. It is summarized
in the fourth commandment: "For in six days the Lord made heaven and earth, the sea,
and all that in them is, and rested on the seventh day ..." (1).
Much more recent is a radically different concept of origins which
derives the present universe from a hypothetical "big bang" and its evolutionary
aftermath. Accordingly, life originated on Earth by random interaction between matter and
energy.
Never before has the phenomenon of life been better understood. This is
due to intense research effort by tens of thousands of scientists and their often
spectacular discoveries over the past 50 to 80 years. The functions of about one-third of
all proteins manufactured by the simple cell Escherichia coli are now known, and
the total elucidation of the structure of this cell is foreseeable (2).
We are also learning more about structures and workings of other more
complex living systems. The recent development of automated DNA sequencing has prompted
suggestions that a multi-billion dollar effort be organized to determine the complete
nucleotide sequence of the human genome.
Cells are the smallest living independent entities, and nothing less
than a cell deserves the adjective "alive." Cells range in complexity from the
simple bacterium, such as the common colon organism Escherichia coli, to highly
differentiated cells of our nervous system. Numerous features common to all cells are
understood by creationists to signify a common designer, but are explained by
evolutionists in terms of a common ancestry.
Common constituents of living matter
All cells have similar components. By weight they are 60-70% water,
25-35% biopolymers, and about 5% small organic compounds and minerals. These cellular
ingredients (with the exception of water and minerals) are unique in several ways and
cannot be found in nature except as parts of living or once-living matter.
Our inanimate environment comprises substances made from comparatively
simple molecules containing a limited number of atoms. These molecules are rich in oxygen
atoms, resistant to heat, and generally stable under a variety of conditions. In contrast
to these simple molecules, biological polymers (which constitute most of living matter
after water is removed) — proteins, nucleic acids, polysaccharides and lipids —
are molecules made from thousands of atoms. They are rich in carbon and hydrogen atoms and
are definitely unstable in the presence of heat and oxygen. Researchers working with
proteins, for example, must always be careful not to stir a protein solution too
vigorously, and to keep it on ice as long as possible, so as to prevent unraveling their
intricate structures.
Protein molecules and nucleic acids are informational
macromolecules, i.e., their structures harbor biological information. The gigantic
molecules of proteins and nucleic acids are made by linking hundreds (or thousands) of a
small number of "building block" molecules: amino acids for proteins and
nucleotides for nucleic acids. Biological information resides in the particular sequence
in which building blocks are linked.
When letters of the alphabet are linked in particular sequences,
meaningful words are created. Likewise, the information content of proteins and nucleic
acids depends initially on the order in which their building block components are
connected.
The true meaning of biological information contained within the
structures of biopolymers is evident only in the context of the entire living cell,
because the phenomenon of life depends on harmonious interactions of thousands of kinds of
protein and nucleic-acid molecules. If biopolymers are like words, then the living cell is
like an extensive monograph.
Biopolymers mixed in test-tubes do not yield living matter
When all biopolymers are removed from a cell and put in a test-tube
with all the other ingredients normally found in cells (small organic molecules and
minerals) in just the right proportions, nothing happens.
The living cell is more than a collection of biologically active
molecules. However, the extra quality is not, as many think, a mysterious life-force which
departs upon death. This may be demonstrated rather dramatically by freeze-dried bacteria.
If a liquid culture of single-celled organisms is frozen rapidly and
placed under vacuum, cellular water in the form of ice gently leaves the cells through
sublimation, leaving behind cells as waterless powder. The organisms are in a state of
suspended animation, neither alive nor dead. They can remain in this state indefinitely,
so long as they are kept dry. If the cells are placed in water along with suitable
nutrients, they once again continue living. Therefore, in this instance "life"
was manipulated simply by adding or removing water.
Why living matter is more than the sum of its ingredients
In a living cell the thousands of chemical transformations that are
necessary for life to occur must be confined to a comparatively small space. This makes
the products of one reaction available as starting materials for the next reaction along
the necessary biochemical metabolic pathways. Moreover, the ingredients of cells are
frequently assigned spatially, some in the nuclear region, others near the cell envelope.
Without cellular morphology, these components have no meaningful tasks.
The process of life is dynamic, involving the biosynthesis of new
substances, degradation of old ones, pumping in fresh food supplies and secreting waste
products, as hundreds of chemical changes take place simultaneously every second. A most
important property of a living cell which makes it more than just the sum of its
ingredients is that the totality of its chemical transformations is not in equilibrium.
A chemical change is the rearrangement of atoms making up various
molecules. Such a change may be represented as: A + B Û C + D, where substances A
and B interact and form products C and D.
After this chemical change runs its course, a certain amount of all four substances will
be present. The ratio at equilibrium of (C*D) to (A*B)
is an unchanging (constant) number. At that point the reaction is incapable of any further
chemical transformation. If all these chemical changes reach equilibrium, the cell dies.
Essentially all chemical reactions in a cell are facilitated by
biological catalysts called enzymes. These agents tend to push reactions rapidly toward
equilibrium, even though total equilibrium would be fatal to the cell. However, since
chemical reactions in the cell are interconnected, the end products of one chemical
transformation become the starting material for the next, and thus equilibrium is never
reached. As the products are further utilized, more starting materials are manufactured,
resulting in constant intracellular concentration of metabolic intermediates. This is
called a steady state, non-equilibrium system, because the amounts of metabolic
intermediates are relatively unchanging within the cell, and the total system is not
at equilibrium. Such is only possible in live, intact cells. If a cell is physically
disrupted or if it dies, the steady state changes into equilibrium. Figure 1 illustrates
in a simple way the contrast between steady state and equilibrium conditions.
FIGURE 1. A simple illustration of the difference between steady-state and equilibrium conditions. In both cases the volume of liquid in the container is constant. However, in A, liquid is constantly flowing through the system, while in B, the liquid is static.
This situation can actually be approximated in the laboratory by
poking holes in the membranes of live cells (so they will lose their ability to
concentrate nutrients from their environment) and allowing the internal reactions to go to
equilibrium. Such cells are now dead, and even if the holes of their membranes were
repaired, they will not come back to life. For life to recur, non-equilibrium conditions
would have to be established by the selective removal of key metabolite molecules from the
cell. When the strategic reactions are once again restored to non-equilibrium, the system
as a whole will be driven toward a steady state.
Manipulations involving the removal of a few small molecules from a
cell containing many other molecules is beyond our present and most likely future
capabilities. Such a capacity is tantamount to being able to reverse death to life on the
cellular level.
Attempts to discover the origin of life
The earliest historical records indicate that man has recognized the
qualitative difference between living and non-living matter, and since then there never
has been a shortage of theories to explain the presence of life on Earth. Yet the origin
of life remains one of the greatest challenges to naturalistic interpretations. According
to Nobel laureate Max Delbruck, "... there has been an immense conceptual gap between
all present-day life and no life," and the "how" of the transition of earth
from no life to life is "perhaps the fundamental question of biology"
(3).
Nevertheless, the immense conceptual gap between life and non-life is
neither recognized nor admitted by many evolutionary theorists. A 1978 review entitled
"Chemical evolution and the origin of life" begins with these words:
"Perhaps the most striking aspect of the evolution of life on earth is that it
happened so fast" (4). More recently, the first chapter of a college textbook on the
molecular biology of the cell contains this summary statement: "Living cells probably
arose on earth by the spontaneous aggregation of molecules about 3.5 billion years
ago" (5).
Regardless of their degree of optimism or enthusiasm, evolutionary
theorists are forced to propose explanations for the spontaneous generation of life from
non-living matter. In order for biological evolution to begin, some starting material is
necessary. This need is met by the postulates of chemical evolution.
When the outlines of modern theories of chemical evolution (the natural
processes on a "pre-biotic earth" which gave rise to the first living matter)
were formulated by A.I. Oparin and J.B.S. Haldane in the 1920s (6), very little was known
about the biochemical intricacies of living matter. Consequently, there was plenty of
freedom to postulate mechanistic processes by which organisms could come into existence.
Modern theories of chemical evolution found in current monographs and
textbooks developed over a span of approximately 60 years. They suggest that early Earth
was covered largely with a warm, slightly alkaline ocean. Though rich in carbon monoxide,
carbon dioxide, ammonia, methane, hydrogen, and nitrogen, the atmosphere definitely did
not contain atomic or molecular oxygen. Ultraviolet light from the sun, geothermal energy
from volcanoes, shock waves from thunder, and cosmic radiation acted upon gases of the
primitive atmosphere causing the formation of biomonomers such as amino acids, sugars,
purines, pyrimidines, and fatty acids. These substances polymerized to form the
proto-types of more recent proteins, nucleic acids and cell membranes. In time they
coalesced to form the first proto-cell, a collection of polymers enclosed in a membrane.
Eventually these protocells became increasingly complex, until the first true living cell
was born.
Laboratory simulations of chemical evolution
The year 1953 was a banner year for chemical evolution. Stanley
Miller, a graduate student working with Nobel prize winner Dr. Harold Urey, published his
experiments on the synthesis of amino acids in a simulated primitive-earth environment.
He built a glass apparatus, in which circulating ammonia, methane,
hydrogen and water vapor were exposed to electrical spark discharges for one week.
Molecules forming in the vapor phase were trapped in water and analyzed. Among the 35
diverse substances identified, 9 were amino acids, almost half of the 20 different kinds
found in proteins (7)!
Miller's paper signaled an onslaught of experiments by numerous
investigators who varied the starting materials, the source of energy and other
experimental parameters. Their efforts yielded 19 of the 20 amino acids, all 5 nitrogenous
bases which are crucial to nucleic-acid formation, and a number of important sugars as
well (8).
These results serve as a pillar on which chemical evolutionists build
their theoretical edifices. Apparently it is indeed possible to envision hypothetical
situations where at least the most important metabolic biomonomers may come into
existence.
The evolutionary scenario requires the continual accumulation of
biomonomers in the primordial ocean until it becomes an "organic soup." The next
necessary step on the chemical evolutionary ladder is to link biomonomers into polymers,
especially proteins and nucleic acids. This involves the removal of a molecule of water
from two biomonomers in order to form a chemical bond between them.
One of the postulates proposed for polymerization assumes that high
concentrations of various amino acids accumulated at the rim of volcanoes, where the high
temperatures drove off the water molecules, leaving proteins behind. Sidney Fox, the chief
proponent of this theory, demonstrated that mixtures of amino acids heated at 200ºC for 6
or 7 hours indeed formed protein-life polymers which he called "protenoids."
These polymers show weak catalytic activities partially resembling enzymes. When
protenoids cool, they form "microspheres" supposedly resembling primitive cells
morphologically (9). These structures can "grow" under favorable conditions and
"divide" by budding. Interesting as these experiments are, their results reveal
serious deficiencies when they are used to support a scenario for chemical evolution.
Deficiencies of laboratory simulations of chemical evolution
The success of the Miller-Urey type experiments depends on the types
of gases introduced into the experimental systems. Early models of chemical evolution
assumed a primordial atmosphere rich in methane, ammonia and molecular hydrogen, and these
gases were used with considerable success. More recent models of the early Earth
atmosphere, based on data from numerous space-probes, see the primordial atmosphere
resulting mainly from the release of volatile materials trapped by solid particles during
the formation of the planet. Thus the composition of an early atmosphere would have
resembled the contents of present-day volcanic fumes. These are rich in carbon dioxide and
water and have minor amounts of nitrogen, hydrogen sulfide and sulfur dioxide. Pre-biotic
simulation experiments using gas mixtures of nitrogen, carbon dioxide and water vapors
produced mostly ammonia and nitric acid in the hands of one investigator and formaldehyde
in another laboratory (10).
Whatever the composition of the primordial atmosphere may have been,
evolutionary theorists agree that it could not have contained atomic or molecular oxygen.
All postulated processes of chemical evolution would cease in the presence of oxygen, for
oxygen would quickly react with organic compounds formed in the atmosphere, oxidizing them
to carbon dioxide and formic acid.
Our present-day atmosphere contains 20% oxygen. A small portion of this
gas is converted to the ozone layer of the upper atmosphere which shields us from
high-energy ultraviolet radiation of the sun. A primordial earth, covered with an
oxygenless atmosphere, would have been subject to the sterilizing effect of ultraviolet
radiation. If, on the other hand, there was a primordial ozone shield, then oxygen also
had to be present at concentrations of at least 1-10% of the current amount.
A potentially important source of pre-biotic oxygen could have been the
photo-dissociation of water by ultraviolet rays. Calculations of theoretical levels of
oxygen in a primordial atmosphere range from essentially nil to 25% of present levels
(11). Support for high rate of oxygen production by dissociation of water vapors comes
from data collected during the Apollo 16 mission, where pictures of Earth were taken from
the moon, using ultraviolet sensitive films. These pictures showed that a gigantic cloud
of hydrogen, extending 40,000 miles into space, surrounded the earth. The source of this
hydrogen could only be water vapor, bombarded by high-energy ultraviolet rays above the
ozone layer
Scientists have examined uranium and iron-containing minerals from the
earliest available sediments, hoping to learn whether the early atmosphere was oxidizing
or reducing. The results were equivocal. We now believe that the existence of reduced
minerals in sediments does not necessarily signify the existence of a reducing atmosphere
and an oxidizing atmosphere does not always produce oxidized minerals. The relationship
between a sediment and its environment cannot be established unless the actual rates of
oxidation or reduction are known.
Two further observations should be made about the significance of the
Miller-Urey type organic-soup-producing experiments. First, a consideration of yields.
Even with the removal of products during experimentation by the use of traps, pre-biotic
simulation experiments generate fairly small amounts of usable products. Assuming no
destruction of molecules in the atmosphere, optimistic estimates ranged as high as 0.001 M
concentration in the primitive ocean. However, when the destructive effect of ultraviolet
radiation on amino acids is taken into account, the upper limit has been given at one ten
millionth molar in the primitive sea, which happens to be the actual concentration of
amino acids in the North Atlantic Ocean (12)!
Such low concentrations of biomonomers would have been inadequate to
polymerize into macromolecules. Though it has been suggested that chemical evolution could
have proceeded in smaller pools where the precursor substances would have been
concentrated, there is no geologic evidence for large deposits of organic substances.
Moreover, if concentration had occurred, undesirable impurities likely would also
accumulate and interfere with polymerization, the next step in chemical evolution.
The second observation is that synthetic reactions outside a cell
produce equal amounts of optical isomers of amino acids and sugars. Therefore the
primordial ocean would have contained a racemic mixture of biomonomers. Since known
biopolymers exclusively utilize only one of the two or more possible isomers in the case
of sugars and amino acids, it is totally incomprehensible how such an arrangement could
develop from a 50-50 mixture of optical isomers.
Thus it is highly unlikely that chemical evolution could have taken
place by the organic-soup mechanism. Among the factors against this mechanism are the
great likelihood of substantial oxygen content in the primitive atmosphere and the small
yields of biologically significant substances which would be present as equal amounts of
optical isomers.
The "volcanic rim" approach of Sidney Fox assumes a
primordial earth covered with an organic soup. It addresses the next difficulty — the
polymerization of biomonomers — by splitting out the water in an aqueous environment,
which, in terms of thermodynamics, is essentially impossible! However, by postulating a
heat source, he dries up the environment and succeeds in the polymerization. But Fox pays
for his success dearly.
The resulting protenoids have only a superficial resemblance to true
proteins, in that the resulting peptide bonds are predominantly of the beta, gamma and
epsilon variety, rather than the naturally occurring alpha bonds. The amino acid sequences
are generated entirely by random means, and there is no mechanism to ensure any
reproducibility. If by chance a biologically useful molecule is formed, how will its
subsequent production be ensured?
When protenoids cool, they form microspheres which, according to Fox,
grow and divide. True growth, however, requires numerous metabolic steps and incorporation
of small molecules into the polymer structure of the cell. In Fox's experiment,
"growth" results from the physical attraction of opposite charges, and
"budding" refers to the breaking up of microspheres due to changes in acidity or
heat.
Since, according to this theory, all this is taking place on the
surface of the earth, one must consider the destructive effect of ultraviolet radiation on
any biologically active structure.
Clearly, the volcanic-rim theory does not advance the cause of chemical
evolution, for it represents a dead-end approach to the problem.
Which came first, the chicken or the egg?
All chemical evolutionary scenarios require the pre-biotic
production of informational macromolecules. An important question to decide, however, is
which type of information biopolymer evolved first, protein or nucleic acid? Proteins are
the catalysts of biochemical processes, whereas nucleic acids contain the genetic
information for specifying the sequence of amino acids in molecules. In living matter
nucleic-acid formation occurs by enzyme catalysis, and protein synthesis is impossible
without nucleic acids. Therefore, evolutionists have to solve a puzzle which resembles the
question, "Which came first, the chicken or the egg?"
Until recently some theoreticians favored the notion that protein
molecules were replicated directly in the absence of nucleic acids, until proteins
"invented" nucleic acids. Others felt that nucleic acids were the first
biopolymers formed, and they in turn "developed" protein synthesis. A third
approach suggested that proteins and nucleic acids co-evolved independent of one another.
These alternatives do not explain satisfactorily the origins of protein
and nucleic-acid duplicating systems. For this reason, the discovery that certain types of
ribonucleic acids had enzymatic activity was quickly adopted into the chemical
evolutionary scenario (13).
In eucaryotic cells, processing of ribonucleic acids often includes the
removal of specific intervening nucleotide sequences called "introns" from the
RNA molecules. It was found that the intron sequences in the ribosomal RNA of the organism
Tetrahymena thermophila spliced themselves without the cooperation of any
protein. Moreover, this piece of RNA molecule exhibits true enzymatic activity in that it
catalyzed the sequence-specific hydrolysis of certain pieces of other RNA molecules.
Introns in fungal mitochondria and in nuclear RNA of higher animals have been also found
to self-splice.
Enzymatically active RNAs are called "ribozymes." Their
properties combine the most desirable elements of both proteins and nucleic acids. It is
not surprising that ribozymes are rapidly taking the center stage among evolutionists as
potentially the most likely biomolecules to have been the precursors of living matter, or
in other terms, to be both "the chicken and the egg" at the same time.
The difficulties with the ribozyme hypothesis are manifold. Before the
existence of RNA in a pre-biotic environment can be postulated, a supply of
ribonucleotides — the monomers of RNA — is needed. Pre-biotic synthesis of
ribose can only occur from the polymerization of fairly high concentrations of
formaldehyde (0.01 M or greater) in alkaline conditions. This reaction yields a mixture of
different sugars, ribose being a minor component.
Condensation of ribose with adenine or guanine in the absence of
enzymes yields a mixture of unnatural nucleosides (13). Phosphorylation of nucleosides to
nucleotides under pre-biotic conditions has not been demonstrated. Condensation of
ribonucleotides to oligoribonucleotides in a pre-biotic environment has difficulties
similar to those found for the condensation of amino acids to form peptide bonds, with the
added problem of having to form 3' to 5' phosphodiester linkages. (There are nine
different ways that two ribonucleotides can be linked by a phosphodiester linkage. Only
one of these linkages is 3' to 5'.)
Alternative chemical evolutionary scenarios
Some evolutionists have recognized many of the difficulties
mentioned above. They observe the high degree of complexity of contemporary organisms and
admit the seemingly impossible task of offering a plausible explanation. However, since
life is present on Earth, and some sort of mechanistic explanation for its existence is
demanded, they continue to search for satisfactory theories.
Dr. Cairns-Smith, a proponent of a new approach to the problem of
chemical evolution, points to a seemingly impossible formation in nature, such as an arch
of stones (Figure 2). How such an arch could have formed one stone at a time requires a
great deal of explaining. But if we assume that it was the top layer of stones of a round
pile, and somehow the "scaffolding" below the top layer was selectively removed,
then we have a reasonable explanation.
FIGURE 2. Two possible ways to form a stone arch. A illustrates an extraordinarily fortuitous set of circumstances. B suggests how such an arch might result from the aggregation of units and subsequent removal of the underlying scaffold. This illustrates how "clay genes" might act as the scaffolding for biomolecules (arch). Figure based on Cairns-Smith (1985).
Attention is called, for example, to crystals of kaolinite (made of
layers of aluminum atoms bound in a network of oxygen and silicon atoms). In any given
region, the aluminum atoms are positioned in one of three possible arrangements. Such a
structure could hold immense amounts of information, which could even be replicated if the
relative position of the aluminum atoms is reproduced in each succeeding layer. These
structures could behave as "clay genes" which carry genetic information and
which, according to Dr. Cairns-Smith, could act as a scaffolding on which present-day
biomolecules of RNA and DNA could form (14).
The scaffold theory bypasses the nitty-gritty details of how a living
cell can come into existence. It tries to show a way by which information may be
transferred in the absence of a biological transfer system. It does not answer where or
how the information originates, neither does it attempt to answer the most obvious
question of how the process from inorganic clay to organic polymers occurs. It is
essentially an armchair exercise, devoid of experimental support.
A group of evolutionists who cannot envision the evolution of living
matter on Earth proposes that life evolved elsewhere in the universe and was imported
accidentally or purposefully from outer space. Panspermia was proposed last century as an
explanation for life after Pasteur disproved the spontaneous generation of life. It
remained quite popular (15), until the organic-soup theory took over in the 1950s. With a
fuller appreciation of the difficulties of the organic-soup theory, panspermia is again
gaining in popularity.
This theory is essentially an admission of failure to give a convincing
naturalistic account for the origin of life on Earth. It pushes the problem out of the
realm of experimentation and gives up on suggesting how life could have come about.
Max Delbruck, a confirmed evolutionist, has observed:
In recent years various theories have outlined the possible connections between molecular selection, natural selection, and irreversible thermodynamics in this prebiotic biochemical trial process. While all these theories seem quite plausible and very intelligent, in my opinion they tell us very little about the origin of life. I have made it my rule not to read this literature on prebiotic evolution until someone comes up with a recipe that says 'do this and do that, and in three months, things will crawl in there.' When someone is able to create life in a shorter time than was originally taken by nature, I will once more start reading that literature (16).
Why life cannot arise spontaneously
Some general considerations take the topic of the origin of life
beyond listing various theories of chemical evolution and a discussion of their
inadequacies. First, there is the tacit assumption by evolutionists that matter possesses
some sort of internal drive which pushes it to self-organize into living structures. It is
as if molecules constituting biopolymers would confer some sort of benefit to their
constituent atoms.
There is no evidence that this is the case. Atoms and molecules respond
to only one type of drive; that is, to exist in the lowest possible state of energy.
Biomolecules are examples of exactly the opposite; they are complexes of atoms in a high
energy state. If atoms had a choice, they would rather get out of being part of the high
energy configurations called proteins and nucleic acids.
All mechanistic explanations of origins have two deficiencies. One
difficulty is in explaining the source of biological information, which ultimately
dictates the structure and function of biopolymers. It is clear that chance cannot provide
this information.
A second consideration which renders all mechanistic explanations
invalid is that life processes are non-equilibrium events. If by chance all necessary
biopolymers and small metabolites could have been produced in the primordial environment,
brought together and enclosed in a membrane, a non-living cell would be the result. In the
very process of assembly, reactants and their catalysts would be brought together,
providing opportunity for individual chemical reactions to reach equilibrium.
There is such a concentration of living organisms on Earth's surface
that it is difficult to locate any area that is sterile. Obviously, life had to start
somehow. The existence of a supernatural Intelligence who is capable of designing and
creating the various living organisms found on Earth is inconceivable to the modern
secular mind which is accustomed to explaining all phenomenon by natural processes. But
this is precisely the lesson to be learned from our chemical evolutionary efforts. Our
inability not only to create living matter but even to suggest how such could come into
existence forces us to admit that the existence of life demands the existence of a
Creator.
REFERENCES
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Geoscience Research Institute. All rights reserved.
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