p. 117. Subtitle: "Scientists are having a hard time agreeing on when, where
and--most important--how life first emerged on the earth."
Mr. Horgan begins by describing the traditional(since 1953) scenario for the
origin of life: Spontaneous formation of amino acids and nucleotides; spontaneous
formation of proteins from amino acids and DNA from nucleotides; spontaneous origin of
first living cells from proteins, DNA, lipids and other simple chemicals.
p. 117. Stanley Miller's 1953 experiment is described, in which he produced a mixture
of amino acids and other compounds by sparking a gas-water mixture.
p. 117. "Pundits speculated that scientists...would shortly conjure up living
organisms in their laboratories and thereby demonstrate in detail how genesis unfolded. It
hasn't worked out that way. 'The problem of the origin of life has turned out to be much
more difficult than I, and most other people envisioned,' says Miller, now a professor of
chemistry at the University of California at San Diego."
Nucleic Acids, in Particular RNA, Replace Proteins as New Candidates for
Originating Life.
p. 119. "Many investigators now consider nucleic acids to be much more plausible
candidates for the first self-replicating molecules...But there is a hitch. DNA cannot do
its work, including forming more DNA, without the help of catalytic proteins, or enzymes.
In short, proteins cannot form without DNA, but neither can DNA form without proteins. To
those pondering the origin of life, it is a classic chicken-and-egg problem: Which came
first, proteins or DNA?"
p. 119. "Walter Gilbert, a biologist at Harvard University, coined the term, 'RNA
world' in 1986 and remains an enthusiastic advocate of the theory. In his view, the first
organisms consisted of simple self-replicating RNA molecules. As they evolved, they
learned to synthesize proteins that could help them replicate faster and lipids that could
form a cell wall. Finally, the RNA organisms gave rise to DNA, which served as a more
reliable repository of genetic information."
A Host of Difficult Problems Arise with the RNA-World Concept.
p. 119. "But as researchers continue to examine the RNA-world concept closely,
more problems emerge. How did RNA arise initially? RNA and its components are difficult to
synthesize in a laboratory under the best of conditions, much less under plausible
prebiotic ones. For example, the process by which one creates the sugar ribose, a key
ingredient of RNA, also yields a host of other sugars that would inhibit RNA synthesis.
Moreover, no one has yet come up with a satisfactory explanation of how phosphorous, which
is a relatively rare substance in nature, became such a crucial ingredient in RNA (and
DNA)."
p. 119. "Once RNA is synthesized, it can make new copies of itself only with a
great deal of help from the scientist, says Joyce of the Scripps Clinic, an RNA
specialist. 'It is an inept molecule,' he explains, 'especially when compared with
proteins.'"
p. 119. "Leslie E. Orgel of the Salk Institute for Biological Studies, who has
probably done more research exploring the RNA-world scenario than any other scientist,
concurs with Joyce. Experiments simulating the early stages of the RNA world are too
complicated to represent plausible scenarios for the origin of life, Orgel says. 'You have
to get an awful lot of things right and nothing wrong,' he adds."
A Substitute for RNA-World Is Proposed but Soon Rejected.
p. 120. "Last summer a group led by Julius Rebek, Jr., a chemist at the
Massachusetts Institute of Technology, created a stir by announcing that it had created a
synthetic molecule that could replicate itself. The molecule, called amino adenosine
triacid ester (AATE), consists of two components that chemically resemble both proteins
and nucleic acids. AATE molecules, when placed in a solution of chloroform stocked with
the components, serve as templates for the formation of new AATEs."
p. 120. "Rebek's experiments have two drawbacks, according to Joyce: they only
replicate in highly artificial, unnatural conditions, and, even more important, they
reproduce too accurately. Without mutation, the molecules cannot evolve in the Darwinian
sense. Orgel agrees. 'What Rebek has done is very clever,' he says, 'but I don't see its
relevance to the origin of life.'"
A General Negative Review of Origin-of-Life Research
p. 120. "'The simplest bacterium is so damn complicated from the point of view of
a chemist that it is almost impossible to imagine how it happened,' says Harold P. Klein
of Santa Clara University, chairman of a National Academy of Sciences committee that
recently reviewed origin-of-life research. (Its conclusion: much more research is
needed.")
A Discussion of Recent Secular Conclusions About Conditions on the Early Earth
p. 121. "It seems, moreover, that the atmosphere's composition during this period
may not have favored the synthesis of organic compounds as much as had been thought. The
traditional view was elucidated in the early 1950s by Harold C. Urey, a Nobel laureate in
chemistry at the University of Chicago. He proposed that the atmosphere was reducing: rich
in hydrogen-based gases such as methane and ammonia, which are abundant on Saturn, Jupiter
and Uranus."
p. 121. "Yet over the past decade or so, doubts have grown about Urey and Miller's
assumptions regarding the atmosphere. Laboratory experiments and computerized
reconstructions of the atmosphere by James C.G. Walker of the University of Michigan at
Ann Arbor and others suggest that ultraviolet radiation from the sun, which today is
blocked by atmospheric ozone, would have destroyed hydrogen-based molecules in the
atmosphere. Free hydrogen would have escaped into space.
"The major component of the atmosphere, these findings suggest, was carbon dioxide
and nitrogen spewed out by volcanoes. Such an atmosphere would not have been conducive to
the synthesis of amino acids and other precursors of life. According to recent
calculations by James F. Kasting of Pennsylvania State University, the carbon dioxide
might also have created a greenhouse effect so extreme that temperatures at the earth's
surface rose nearly to the boiling point of water."
Hot Sea Bottom Vents Proposed as Sites for Origin of Life, but Criticisms Soon
Arise.
p. 122. "Miller does not like vents at least, not as the original seats of life.
He notes that modern vents seem to be short-lived, lasting only for a few decades before
they are plugged up. Moreover, he and Jeffrey L. Bada, who is also at the University of
California at San Diego, have done experiments that suggest the superheated water inside
the vents--which sometimes exceeds 300 degrees Celsius (572 degrees Fahrenheit)--would
destroy rather than create complex organic compounds. If the surface of the earth is a
frying pan, Miller says, a hydrothermal vent is the fire."
Theories Based on Sulfur Compounds and Sea Bottom Vents Proposed and Criticized.
p. 122. "...Wächterhäuser's proposal is unique in its details...The first cell,
he conjectures, might have been a grain of pyrite enclosed in a membrane of organic
compounds. The cell could have reproduced if the pyrite grain grew a new crystalline 'bud'
that became encapsulated in its own membrane and broke free."...but Wächterhäuser
himself admits that his theory is for the most part still 'pure speculation.'"
p. 122. "Joyce suspects that Wächterhäuser's legal skills may have helped him
win more acceptance for his theory than it deserves. 'He's an excellent advocate for his
case,' Joyce observes..."
p. 123. "De Duve proposes that thioesters in the primordial ooze could have
triggered a cascade of chemical reactions resembling those occurring in modern cellular
metabolism. The reactions would have been catalyzed by 'proto-enzymes,' also formed from
thioesters. The reactions would eventually result in the synthesis of ribonucleic acids,
thereby ushering in the RNA world."
p. 123. "'I'd love to see the experimental evidence,' Miller says."
p. 123. "'What de Duve neglected to say,' Cairns-Smith notes, 'is that this
process makes the oceans less suited for the synthesis of organic molecules.'"
pp. 123-4. "...Cairns-Smith has been pushing his own hypothesis...he proposes that
life arose on a solid substrate...he prefers crystalline clays to pyrite...clay crystals
have enough complexity to mutate and evolve in a lifelike way. Some clays might have
become still better breeders by developing the ability to attract or synthesize organic
compounds--such as nucleic acids or proteins. Eventually, the organic compounds would
become sophisticated enough to begin replicating and evolving on their own."
p. 125. "Unlike some origins-of-life theorists, Cairns-Smith cheerfully admits the
failings of his pet hypothesis: no one has been able to coax clay into something
resembling evolution in a laboratory; nor has anyone found anything resembling a
clay-based organism in nature...Organic molecules are too wiggly to work,' he says."
The Weirdest of all Hypotheses--Directed Panspermia
p. 125. "About a decade ago Orgel and Crick managed to provoke the public and
their colleagues by speculating that the seeds of life were sent to the earth in a
spaceship by intelligent beings living on another planet. Orgel says the proposal, which
is known as directed panspermia, was 'sort of a joke.' But he notes that it had a serious
intent: to point out the inadequacy of all explanations of terrestrial genesis. As Crick
once wrote: The origin of life appears to be almost a miracle, so many are the conditions
which would have had to be satisfied to get it going.'"
Some Critical Remarks by "Mr. Origin of Life"--and His Confession of
Faith
p. 125. "Miller, who after almost four decades is still in hard pursuit of life's
biggest secret, agrees that the field needs a dramatic finding to constrain the rampant
speculation...What the field needs now, Miller comments, is not more theories or far-flung
searches for alien life but more experiments. 'I come up with a dozen ideas a day, and I
usually discard'--he reflects for a moment--'the whole dozen.'
Does he ever entertain the possibility that genesis was a miracle not reproducible by
mere humans? Not at all, Miller replies. 'I think we just haven't learned the right tricks
yet,' he says. 'When we find the answer, it will probably be so d----d simple that we'll
all say, 'Why didn't I think of that before?'"
