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The Miller-Urey Experiment Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education THE MILLER-UREY how the early atmosphere was probably differ- EXPERIMENT ent from the atmosphere hypothesized in the original experiment. Wells then claims that the THE EXPERIMENT ITSELF actual atmosphere of the early earth makes the he understanding of the origin of life Miller–Urey type of chemical synthesis was largely speculative until the 1920s, impossible, and asserts that the experiment Twhen Oparin and Haldane, working does not work when an updated atmosphere is independently, proposed a theoretical model used. Therefore, textbooks should either dis- for “chemical evolution.” The Oparin– cuss the experiment as an historically interest- Haldane model suggested that under the ing yet flawed exercise, or not discuss it at all. strongly reducing conditions theorized to have Wells concludes by saying that textbooks been present in the atmosphere of the early should replace their discussions of the Miller– earth (between 4.0 and 3.5 billion years ago), Urey experiment with an “extensive discus- inorganic molecules would spontaneously sion” of all the problems facing research into form organic molecules (simple sugars and the origin of life. amino acids). In 1953, Stanley Miller, along These allegations might seem serious; how- with his graduate advisor Harold Urey, tested ever, Wells’s knowledge of prebiotic chemistry this hypothesis by constructing an apparatus is seriously flawed. First, Wells’s claim that that simulated the Oparin-Haldane “early researchers are ignoring the new atmospheric earth.” When a gas mixture based on predic- data, and that experiments like the Miller– tions of the early atmosphere was heated and Urey experiment fail when the atmospheric given an electrical charge, organic compounds composition reflects current theories, is simply were formed (Miller, 1953; Miller and Urey, false. The current literature shows that scien- 1959). Thus, the Miller-Urey experiment tists working on the origin and early evolution demonstrated how some biological molecules, of life are well aware of the current theories of such as simple amino acids, could have arisen the earth’s early atmosphere and have found abiotically, that is through non-biological that the revisions have little effect on the processes, under conditions thought to be sim- results of various experiments in biochemical ilar to those of the early earth. This experiment synthesis. Despite Wells’s claims to the con- provided the structure for later research into trary, new experiments since the Miller–Urey the origin of life. Despite many revisions and ones have achieved similar results using vari- additions, the Oparin–Haldane scenario ous corrected atmospheric compositions remains part of the model in use today. The (Figure 1; Rode, 1999; Hanic et al., 2000). Miller–Urey experiment is simply a part of the Further, although some authors have argued experimental program produced by this para- that electrical energy might not have efficient- digm. ly produced organic molecules in the earth’s early atmosphere, other energy sources such as WELLS BOILS OFF cosmic radiation (e.g., Kobayashi et al., 1998), ells says that the Miller–Urey exper- high temperature impact events (e.g., iment should not be taught because Miyakawa et al., 2000), and even the action of Wthe experiment used an atmospheric waves on a beach (Commeyras et al., 2002) composition that is now known to be incorrect. would have been quite effective. Wells contends that textbooks don’t discuss Even if Wells had been correct about the 3 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education Researcher(s) Year Reactants Energy source Results Probability Miller 1953 CH4, NH3, H2O, H2 Electric discharge Simple amino acids, unlikely organic compounds Abelson 1956 CO, CO2, N2, NH3, H2, Electric discharge Simple amino acids, unlikely H2O HCN Groth and Weyssenhoff 1957 CH4, NH3, H2O Ultraviolet light Simple amino acids (low under special conditions (1470–1294 ?) yields) Bahadur, et al. 1958 Formaldehyde, Sunlight Simple amino acids possible molybdenum oxide (photosynthesis) Pavolvskaya and 1959 Formaldehyde, nitrates High pressure Hg lamp Simple amino acids possible Pasynskii (photolysis) Palm and Calvin 1962 CH4, NH3, H2O Electron irradiation Glycine, alanine, aspartic under special conditions acid Harada and Fox 1964 CH4, NH3, H2O Thermal energy 14 of the “essential” under special conditions (900–1200º C) amino acids of proteins Oró 1968 CH4, NH3, H2OPlasma jet Simple amino acids unlikely Bar-Nun et al. 1970 CH4, NH3, H2O Shock wave Simple amino acids under special conditions Sagan and Khare 1971 CH4, C2H6, NH3, H2O, Ultraviolet light (>2000 Simple amino acids (low under special conditions H2S ?) yields) Yoshino et al. 1971 H2, CO, NH3, Temperature of 700°C Glycine, alanine, unlikely montmorillonite glutamic acid, serine, aspartic acid, leucine, lysine, arginine Lawless and Boynton 1973 CH4, NH3, H2O Thermal energy Glycine, alanine, aspartic under special conditions acid, ?-alanine, N-methyl-?-alanine, ?-amino-n-butyric acid. Yanagawa et al. 1980 Various sugars, Temperature of 105°C Glycine, alanine, serine, under special conditions hydroxylamine, aspartic acid, glutamic inorganic salts, acid Kobayashi et al. 1992 CO, N2, H2O Proton irradiation Glycine, alanine, aspartic possible acid, ?-alanine, glutamic acid, threonine, ?-aminobutyric acid, serine Hanic, et al. 1998 CO2, N2, H2O Electric discharge Several amino acids possible Figure 1. A table of some amino acid synthesis experiments since Miller–Urey. The “probabili- ty” column reflects the likelihood of the environmental conditions used in the experiment. Modified from Rode, 1999. Miller–Urey experiment, he does not explain since 1961 (see Oró, 1961; Whittet, 1997; that our theories about the origin of organic Irvine, 1998). Wells apparently missed the vast “building blocks” do not depend on that exper- body of literature on organic compounds in iment alone (Orgel, 1998a). There are other comets (e.g. Oró, 1961; Anders, 1989; Irvine, sources for organic “building blocks,” such as 1998), carbonaceous meteorites (e.g., Kaplan meteorites, comets, and hydrothermal vents. et al., 1963; Hayes, 1967; Chang, 1994; All of these alternate sources for organic mate- Maurette, 1998; Cooper et al., 2001), and con- rials and their synthesis are extensively dis- ditions conducive to the formation of organic cussed in the literature about the origin of life, compounds that exist in interstellar dust clouds a literature that Wells does not acknowledge. (Whittet, 1997). In fact, what is most striking about Wells’s Wells also fails to cite the scientific litera- extensive reference list is the literature that he ture on other terrestrial conditions under which has left out. Wells does not mention extrater- organic compounds could have formed. These restrial sources of organic molecules, which non-atmospheric sources include the synthesis have been widely discussed in the literature of organic compounds in a reducing ocean 4 Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong Alan D. Gishlick, National Center for Science Education (e.g., Chang, 1994), at hydrothermal vents troversy is really over why it took so long for (e.g., Andersson, 1999; Ogata et al., 2000), and oxygen levels to start to rise. Current data in volcanic aquifers (Washington, 2000). A show that oxygen levels did not start to rise cursory review of the literature finds more than significantly until nearly 1.5 billion years after 40 papers on terrestrial prebiotic chemical syn- life originated (Rye and Holland, 1998; thesis published since 1997 in the journal Copley, 2001). Wells strategically fails to clar- Origins of life and the evolution of the bios- ify what he means by “early” when he discuss- phere alone. Contrary to Wells’s presentation, es the amount of oxygen in the “early” atmos- there appears to be no shortage of potential phere. In his discussion, he cites research sources for organic “building blocks” on the about the chemistry of the atmosphere without early earth. distinguishing whether the authors are refer- Instead of discussing this literature, Wells ring to times before, during, or after the period raises a false “controversy” about the low when life is thought to have originated. Nearly amount of free oxygen in the early atmos- all of the papers he cites deal with oxygen lev- phere. Claiming that this precludes the sponta- els after 3.0 billion years ago. They are irrele- neous origin of life, he concludes that vant, as chemical data suggest that life arose “[d]ogma had taken the place of empirical sci- 3.8 billion years ago (Chang, 1994; Orgel, ence” (Wells, 2000:18). In truth, nearly all 1998b), well before there was enough free researchers who work on the early atmosphere oxygen in the earth’s atmosphere to prevent hold that oxygen was essentially absent during Miller–Urey-type chemical synthesis. the period in which life originated (Copley, Finally, the Miller–Urey experiment tells us 2001) and therefore oxygen could not have nothing about the other stages in the origin of played a role in preventing chemical synthesis. life, including the formation of a simple genet- This conclusion is based on many sources of ic code (PNA or “peptide”-based codes and data, not “dogma.” Sources of data include RNA-based codes) or the origin of cellular fluvial uraninite sand deposits (Rasmussen and membranes (liposomes), some of which are Buick, 1999) and banded iron formations discussed in all the textbooks that Wells (Nunn, 1998; Copley, 2001), which could not reviewed. The Miller–Urey experiment only have been deposited under oxidizing condi- showed one possible route by which the basic tions. Wells also neglects the data from pale- components necessary for the origin of life osols (ancient soils) which, because they form could have been created, not how life came to at the atmosphere–ground interface, are an be.
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