In 1952 biochemist Stanley Miller performed what was heralded as "the first laboratory synthesis of organic compounds under primitive earth conditions."1 This experiment was widely touted as evidence for a naturalistic explanation of life's origin.2 Modern theory and texts still lean heavily on Miller's "proof" of spontaneous generation.
For many reasons, including Miller's prestige as a student of Nobel laureate Harold Urey, few have been willing to question Miller's results. Those who have challenged them include Robert Shapiro, Walter Bradley, Roger Olsen, and Charles Thaxton,3-4 and their challenges have yet to be answered. Let me review their objections, briefly.
The laboratory synthesized compounds were mostly tars. Just a small percentage (at best) of amino acids showed up in the end products, and of the amino acids emerging, most were the two simplest, glycine and alanine. While Miller's carefully controlled "soup" did produce eight of the twenty amino acids needed to build proteins, it produced them in "racemic mixture" (equal quantities of left- and right-handed amino acids). For some still unknown reason, only left-handed amino acids can be used to build proteins. None of Miller's amino acids had combined with others, let alone in the precise sequences needed for protein function.
Miller's experimental conditions were far from naturalistic. Experimental runs took many hours if not days to set up. Most produced negative results. And the chemical conditions were kept strongly reducing (that is, the environment was kept scrupulously free of oxygen) in contradiction with known conditions on Earth at the time of life's origin.
Forty-three years later Miller is seeking to demonstrate a naturalistic path for the synthesis of nucleotides, the building blocks of RNA and DNA molecules. RNA, along with the proteins and DNA, are the molecular machines that allow organisms to perform work and reproduce. RNA molecules are comprised of specific sequences of thousands of four relatively simple molecules (32 to 36 atoms each): adenine, guanine, cytosine, and uracil, plus ribose, a sugar. DNA molecules are comprised of sequences of up to millions of molecules of adenine, guanine, cytosine, and thymine, plus deoxyribose, another sugar. Two of these molecules, adenine and guanine, were synthesized in 1974 by Miller and others in laboratory experiments under so-called "simulated early earth conditions."5 But three molecules, cytosine, uracil, and thymine, for years defied all attempts.
On June 19, 1995, Miller and his colleague Michael Robertson claimed success.6 concentrated solutions of cyanoacetaldehyde and urea heated to 100º Centigrade (212º Fahrenheit) in a sealed tube finally yielded some cytosine. Then, by subtracting water from cytosine, the researchers were able to make some uracil. Miller and Robertson express confidence that these molecules can form under natural conditions.
The scenario they propose is a seawater tidal pool or lagoon slowly evaporating under a hot noonday sun. Such pools and lagoons are known to contain very low concentrations of urea and cyanoacetylene. Laboratory experiments demonstrate that cyanoacetaldehyde can be created by subtracting water from cyanoacetylene. Therefore, if the right pool or lagoon experiences enough evaporation and heating, Miller and Robertson declare, cytosine and uracil will be produced.
How realistic is Miller and Robertson's assertion that tidal pools can produce all four of the building blocks, or nucleotides, for RNA molecules? First, they admit in their discovery paper that the "simulated early earth conditions" under which the other two building blocks of RNA molecules, adenine and guanine, were synthesized required freezing conditions rather than near boiling conditions.7 Thus I surmise that we cannot expect the same pool to make all four of RNA's building blocks. Nor is it reasonable for two pools in close proximity to make all four, plus the necessary sugars. Nor is it reasonable for a nucleotide-rich pool to be undisturbed long enough under the right chemical conditions for the four RNA nucleotides to begin to self assemble-and to link with only right-handed ribose molecules, as life requires.
More importantly, can tidal pools really generate these nucleotides at all? There is an immeasurable difference between the work of clever chemists applying many years of concentrated, well-funded research to construct these building blocks in laboratory test tubes and flasks and the accident of some naturally occurring tidal pool's spontaneously producing such molecules. If there is any truth to Miller and Robertson's scenario, it should be possible to find a natural pool relatively unaffected by modern life where adenine, guanine, cytosine, and uracil have spontaneously arisen.
Randomly strewn bricks do not make a building. No origin-of-life researcher has ever shown us how amino acids and nucleotides can come together under natural conditions to make the proteins, RNA molecules, and DNA molecules, to put all these complex molecules together in the right locations and right environmental conditions, and to turn the ignition switch that sparks the whole network of molecules to life. Clearly intellect and power, not random natural processes, produced life.
References
| 1. | Stanley I. Miller, The Heritage of Copernicus, ed. By J. Neyman (Cambridge, Mass.: MIT Press, 1974), p. 228. |
| 2. | Robert Shapiro, origins: A Skeptic's Guide to the Creation of Life on Earth (New York: Simon & Schuster, 1986), pp. 98-99. |
| 3. | Shapiro, pp. 98-131. 4. Charles B. Thaxton, Walter L. Bradley, and Roger L. Olsen, The Mystery of Life's Origin: Reassessing Current Theories (New York: Philosophical Library, 1984), pp. 42-66. |
| 5. | Stanley L. Miller and L. E. Orgel, The Origins of Life on Earth (Englewood Cliffs, N.J.: Prentice-Hall, 1974). |
| 6. | Michael P. Robertson and Stanley L. Miller, "An Efficient Prebiotic Synthesis of Cytosine and Uracil," Nature, 375 (1995), pp. 772-774. |
| 7. | Robertson and Miller, p. 773. |