“…rampant speculation….I’m sure I’m right…”
Professor Richard Dawkins,
“we are survival machines – robot vehicles blindly programmed to preserve the selfish molecules known as genes.”
Author Tom Robbins,
“Humans were invented by water as a means of transporting itself from place to place.”
Genesis 1:27,
“God created man in His image; in the image of God He created him. He created them male and female.”
This post is intended for your information purposes only and will present a succinct version of John Horgan’s article “In the Beginning…” which appeared in Scientific American (Vol. 264, February 1991, pp. 116-125) the science journal for which he was a senior writer from 1986 to 1997.
He begins the article thusly, “Scientists are having a hard time agreeing on when, where and-most important-how life first emerged on the earth.”
He precedes his review of various theories for life’s origins and categorizes them under the following titles:
Making a 747Chicken or Egg?Scum of the EarthSulfur StoriesFeet of ClaySpace InvadersAre We Alone?
Genesis in Silicon
The rest of this post consists of portions of John Horgan’s article categorized as indicate above:
The intro states, in part:
Some investigators concluded that the first organisms consisted of RNA and that an early ‘RNA world’ had provided a bridge from simple chemistry to prototypes of the complex DNA-based cells found in modern organisms. According to the fossil record, such cells emerged within the first billion years after the earth had formed 4.5 billion years ago. Although this scenario is already ensconced in textbooks, it has been seriously challenged of late. Tests of the RNA-world hypothesis have shown that RNA is difficult to synthesize in the conditions that probably prevailed when life originated and that the molecule cannot easily generate copies of itself.
“Making a 747”
Some scientists have argued that, given enough time, even apparently miraculous events become possible-such as the spontaneous emergence of a single-cell organism from the random couplings of chemicals. Yet Fred Hoyle, the iconoclastic British astronomer, has said such an occurrence is about as likely as the assemblage of a 747 by a tornado whirling through a junkyard…
“Chicken or Egg?”
Many investigators now consider nucleic acids to be much more plausible candidates for the first self-replicating molecules…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?…
RNA might be the first self-replicating molecule…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 phosphorus, which is a relatively rare substance in nature, became such a crucialingredient in RNA (and DNA). 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’…
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…
Nucleic acid chemistry, Orgel points out, rests on a broad foundation of knowledge, and once researchers venture away from this realm, they will be starting virtually from scratch. ‘That would be a major business,’ he says…
Julius Rebek, Jr., a chemist at the Massachusetts Institute of Technology…created a synthetic organic molecule that could replicate itself [amino adenosine triacid ester (AATE)]…Rebek’s experiments have two drawbacks, according to Joyce [Gerald F. Joyce of the Research Institute of Scripps Clinic]: 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’…
‘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…
Even if scientists do create something with lifelike properties in the laboratory, they must still wonder: Is that how it happened in the first place?…
“Scum of the Earth”
Of course, establishing the conditions under which life emerged requires knowing when it emerged…
J. William Schopf of the University of California at Los Angeles…and others have accumulated what they believe is unequivocal evidence that life existed at least 3.5 billion years ago…lumpy, greenish-brown rocks that were once stromatolites…The other fossils show the microscopic imprints of strings of cells resembling modern cyanobacteria, also called blue-green algae…Manfred Schidlowski of the Max Planck Institute for Chemistry in Mainz, thinks he has found evidence that photosynthetic organisms existed even earlier. The evidence comes from 3.8-billion-yearold, partially melted sedimentary rocks from Isua, Greenland…
This attempt to extend the fossil record further back into time has met with some skepticism. David J. Des Marais of NASA Ames says the carbon signature in the Isua rocks is simply too faint to interpret. Roger Buick, an Australian paleontologist now at Harvard…The stromatolites could be sediments distorted by geologic processes, Buick asserts, and the microfossils look to him like ‘little streaks of [excrement].’ He calls them ‘dubio-fossils.’…Other experts on so-called Archaean fossils, including Donald R. Lowe of Stanford University, think Buick, and perhaps even Des Marais, is being too skeptical…
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. It was Urey’s work that inspired Miller, a student of Urey’s, to conduct his 1953 experiment. 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 molecule’s in the atmosphere. Free hydrogen would have escaped into space…
Miller, for one, points out that smoke and clouds could have shielded the delicate hydrogen-based gases from ultraviolet radiation. ‘You have a chorus of people with mathematical models saying there is no methane,’ he says, ‘but they have absolutely no real evidence’…
In the late 1970s scientists discovered several hydrothermal vents on the sea floor…The vents support thriving communities of life…whose primary source of energy is not light but sulfur compounds emitted by the vents…
“Sulfur Stories”
[Stanley Miller] calls the…the vent hypothesis ‘garbage’….Miller does not like vents-at least, not as the original seats of life. He notes that modem vents seem to be short-lived, lasting only for a few decades before they are plugged up. Moreover, he and Jeffrey L. Bada…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 Fahrenhei)-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…
The latest and most unusual theory of this type comes from Gunter Wachtershauser, who is himself an unusual theorist. A practicing attorney…however, he gained a doctorate in organic chemistry and an abiding interest in the origin of life…Whereas most investigators have assumed that life began when some relatively simple compound began to make copies of itself in a solution, he speculated that life started as a metabolic process-a cyclic chemical reaction that is driven by some source of energy-taking place on the surface of a solid. These ideas have precedents, but Wachtershauser’s proposal is unique in its details. It calls for a very specific solid surface: one made of pyrite, or fool’s gold, a metallic mineral consisting of
one iron and two sulfur molecules…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 Wachtershauser himself admits that his theory is for the most part still ‘pure speculation’…
Joyce suspects that Wachtershauser’s legal skills may have helped him win more acceptance for his theory than it deserves…
Christian R. de Duve, a professor emeritus at the Rockefeller University, who won a Nobel Prize in 1974 for his work on cellular structure [his theory] revolves around sulfur-based compounds…[he] proposes that thioesters in the primordial ooze could have triggered a cascade of chemical reactions…The reactions would have been catalyzed by ‘protoenzymes,’ also formed from thioesters. The reactions would eventually result in the synthesis of ribonucleic acids, thereby ushering in the RNA world…
‘I’d love to see the experimental evidence,’ Miller says. Yet he acknowledges that experimentalists like himself may have neglected sulfur-based chemistry for a reason that is not purely scientific: ‘Sulfur smells. It would smell up your whole lab’…
“Feet of Clay”
A. G. Cairns-Smith, a chemist at the University of Glasgow, says he has a good reason to doubt de Duve’s theory: it depends on a proposal, advanced by himself and David C. Mauzerall of Rockefeller, which suggests how a reaction involving iron and water might have enriched the primordial atmosphere with hydrogen. ‘What de Duve neglected to say,’ Cairns-Smith notes, ‘is that this process makes the oceans less suited for the synthesis of organic molecules’… he proposes that life arose on a solid substrate that occurs in vents and almost everywhere else, but he prefers crystalline clays to pyrite…
Unlike some origin-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. Yet he argues that no theory requiring organic compounds to organize and replicate without assistance is likely to fare any better. ‘Organic molecules are too wiggly to work,’ he says…
[Stanley Miller] calls the…pyrite theory ‘paper chemistry’…
“Space Invaders”
If neither the atmosphere nor vents provide a likely locale for the synthesis of complex organic compounds, maybe they were imported from somewhere else: outer space. Juan Oro of the University of Houston raised this possibility as early as the 1960s…
in 1989…the discovery of amino adds just above and below a layer of day deposited at the Cretaceous-Tertiary boundary. Bada and Meixun Zhao, also at San Diego, determined that the amino acids were nonbiological types found previously only in meteorites….
But questions remained: Why were the amino acids found above and below the Cretaceous-Tertiary layer and not within it? And how did the amino adds survive the enormous heat created by the impact? Calculations by Christopher F. Chyba, a planetary scientist at Cornell University, and others suggested that any extraterrestrial object large enough to supply significant amounts of organic material to the earth would generate so much heat during its impact that most of the material would be incinerated…
‘It’s too much like manna from heaven,’ says Sherwood Chang of NASA Ames, an authority on extraterrestrial organic compounds…
Theories giving impacts a role in genesis ‘are very trendy right now,’ he adds, ‘but they are also very speculative’…
This theory [panspermia] was proposed at the end of the last century by the Swedish chemist Svante A. Arrhenius, who asserted that microbes floating throughout the universe served as the ‘seeds of life’ on earth. In modern times Hoyle and…Sri Lankan astronomer N. Chandra Wickramasinghe…continue to promulgate this notion, even arguing that extraterrestrial microbes are the cause of influenza, AIDS and other diseases. Most scientists utterly reject these assertions, declaring that microbes have never been found in space and are unlikely to be, since space is so inimical to life. Yet experiments done by J. Mayo Greenberg, an astrophysicist at the University of Leiden in the Netherlands…concluded that a naked cell could survive for hundreds of years in space-and for as many as 10 million years if it is protected from radiation by a thin shell of ice. Greenberg notes that it is still difficult to imagine how organisms could escape other planets or descend to this one intact. Like most other scientists, he believes life was created on the earth. Nevertheless, he says the panspermia hypothesis, while perhaps improbable and certainly distasteful to many scientists, cannot be ruled out on the basis of his experiments. 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.’
[Stanley Miller] calls the organic-matter-from-space concept ‘a loser’
Mariano’s aside:
I thought to break in here for a note regarding Crick’s views on directed panspermia. Precisely one year after the publication of John Horgan’s “In the Beginning…” Scientific American (February 1992, pp. 16-17) published “The Mephistopheles of Neurobiology” which featured Crick in the “Profile” section. In part the feature reads thusly:
“he [Crick] adds, people must purge themselves of archaic thinking patters-especially those related to religion. ‘One of the most frightening things in the Western world, and this country in particular, is the number of people who believe in things that are scientifically false,’ he says. ‘If someone tells me that the earth is less than 10,000 years old, in my opinion he should see a psychiatrist.’ Some scientists said the same of Crick in 1981 after the appearance of Life Itself, a book on the origin of life that he co-authored with Leslie E. Orgel of the Salk Institute. The book proposed that the seeds of life were sent to the earth in a spaceship launched by beings on another planet. Called directed panspermia, the theory met with derision from other scientists, and Orgel himself described it recently as ‘sort of a joke.’ But Crick insists that given the weaknesses of all theories of terrestrial genesis, directed panspermia should still be considered ‘a serious possibility.'”
And now, back to your regularly scheduled program.
“Are We Alone?”
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…
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…
“Genesis in Silicon”
Stuart A. Kauffman, a biologist who shuttles between the University of Pennsylvania and the Santa Fe Institute in New Mexico…the simulations demonstrate that a system supplied with a sufficient number of such [“generic”] polymers will undergo a ‘phase transition’ that causes it to become ‘auto-catalytic.’ That is, the system will spontaneously begin generating polymers of ever greater complexity and catalytic capability. Kauffman says he is absolutely convinced…Asked if he has any test-tube results to back up his computer simulations, Kauffman replies: ‘No one has done this in post, but I’m sure I’m right.’…’Running equations through a computer does not constitute an experiment,’ sniffs Stanley L. Miller…Gerald Joyce…another test-tube type, is also skeptical…
