by Charles Baum
p. 101).
p. 167
One of the stages: A vast literature addresses the origin of bio-
logical chirality. Comprehensive reviews have been presented by Bonner
(1991, 1995).
p. 169
global excess: Meticulous analyses of amino acids in some me-
teorites have revealed a small but significant excess of L-amino acids (Cronin
and Pizzarello 1983, Engel and Macko 1997, and Pizzarello and Cronin
2000).
278
GENESIS
p. 169
Louis Pasteur: Pasteur (1848).
p. 169
polarized light: Numerous recent articles explore this idea (S.
Clark 1999, Podlech 1999, and Bailey et al. 1998).
p. 169
parity violations: See, for example, Salam (1991).
pp. 169-170
local, as opposed to global: Some authors claim that an
important philosophical distinction exists between deterministic global
models of life (i.e., that some intrinsic feature of the universe demands left-
handed amino acids) versus a chance local selection of left or right (i.e., life
might have formed either way through stochastic processes). Note, however,
that of the many symmetry-breaking models proposed, parity violations in
beta decay provide the only truly universal chiral influence. Most authors
conclude that this effect is so small as to be negligible in any realistic calculations of chiral selection (Bonner 1991, 1995). All other proposed symmetry-
breaking mechanisms are local, though at vastly different scales (i.e., Popa
1997). Circularly polarized light from rapidly rotating neutron stars, for ex-
ample, may selectively break down right-handed amino acids in one sub-
stantial volume of galactic space but will have the opposite effect in other
volumes. Even if such a scenario led to a preponderance of left-handed
amino acids in our region of the galaxy, an equal volume of space would
have featured an excess of right-handed molecules.
p. 170
local environments abounded: Goldschmidt (1952), Lahav
(1999), and Hazen (2004).
p. 171
Albert Eschenmoser: Eschenmoser (1994, 2004) and Bolli et
al. (1997).
p. 173
For most of the twentieth century: For example, Ferris and
Ertem (1992, 1993), Arrhenius et al. (1993), Gedulin and Arrhenius (1994),
Pitsch et al. (1995), Ferris et al. (1996), Ertem and Ferris (1996, 1997), Hill et al. (1998), Liu and Orgel (1998), J. V. Smith (1998), Parsons et al. (1998), and
J.V. Smith et al. (1999). See Chapter 12.
p. 173
three separate points: See, for example, Davankov (1997).
p. 173
By the 1930s: Tsuchida et al. (1935) and Karagounis and
Coumonlos (1938). More recent work by Bonner et al. (1975) casts doubt
on these accounts.
p. 173
experiments were flawed: For a more extensive discussion see
Hazen and Sholl (2003) and Hazen (2004).
p. 174
Edward Dana’s A Textbook: Dana (1958).
p. 181
Glenn’s research: The study of amino acid racemization was
pioneered by Ed Hare (Hare and Mitterer 1967, 1969; Hare and Abelson
1968) of the Carnegie Institution’s Geophysical Lab (with whom Goodfriend
worked for many years) and Jeffrey Bada (Bada et al. 1970, Bada and
Schroeder 1972, and Bada 1972) of the Scripps Institution of Oceanography.
NOTES
279
Hare and Bada developed a bitter rivalry, fueled by disagreements over pri-
ority in this research.
p. 181
But his biggest and boldest: Goodfriend and Gould (1997).
See also Goodfriend et al. (2003).
p. 183
aspartic acid had to be chemically modified: Goodfriend
(1991).
p. 184
We wrote up the results: Hazen et al. (2001). This episode high-
lights a recurrent problem in science: When does an experiment end (Galison
1987)? We had collected sufficient data, replicated on four crystals, and per-
formed with duplicate runs and analyses, to provide statistically meaningful
conclusions. This proof of concept therefore constituted a “publishable unit.”
p. 185
visit from Steve Gould: Gould’s (2002) mammoth book ap-
peared in March 2002 to much notice and grudging admiration. In spite of
his cancer, he returned to D.C. in April 2002 for book signings.
INTERLUDE—
WHERE ARE THE WOMEN?
p. 187
“Where are the women?”: [Sara Seager to RMH, 14 November
2004]
14
WHEELS WITHIN WHEELS
p. 191
“The origin of metabolism . . .”: Dyson (1985, 1999).
p. 191
cosmic imperative: de Duve (1995a).
p. 192
which one came first: The dichotomy between metabolism-
first and genetics-first models is discussed by Lahav (1999, p. 189 et seq.)
and Wills and Bada (2000, pp. 137-139). For varied viewpoints, see, for ex-
ample, Dyson (1999), Morowitz (1992), de Duve (1995a), Orgel (1998a),
and E. Smith and Morowitz (2004).
p. 192
Those who favor genetics: E. Smith and Morowitz (2004, p.
21) note: “One of the striking sociological features of biology today is the
extraordinary importance placed on the sequencing and interpretation of
DNA.”
p. 193
Self-Replicating Molecules: For a general overview of self-
replicating molecules, see E. K. Wilson (1998).
p. 194
Julius Rebek, Jr.: Much of Rebek’s work on self-complementary
molecules was performed while he was Camille Dreyfus Professor of Chem-
istry at MIT. This work is described in Tjivikua et al. (1990); Rebek (1994,
2002); Conn and Rebek (1994); and Wintner et al. (1994).
280
GENESIS
p. 194
Reza Ghadiri: Lee et al. (1996). See also Kauffman (1996) and
Yao et al. (1997).
p. 194
Self-complementary strands: Von Kiedrowski (1986). See also
Sievers and von Kiedrowski (1994) and Li and Nicolaou (1994).
p. 196
“It has not escaped . . .”: Watson and Crick (1953, p. 737).
p. 196
Stuart Kauffman: Many of Kauffman’s ideas are summarized
in two books, The Origins of Order (Kauffman 1993) and At Home in the Universe (Kauffman 1995).
p. 197
“autocatalytic networks”: An important theoretical treatment
of the evolution of autocatalytic systems, called “the hypercycle,” has been
developed by Manfred Eigen of the Max Planck Institute for Biophysical
Chemistry (Eigen 1971; Eigen and Schuster 1977, 1978a, 1978b, 1979). For a
useful analysis, see Fry (2000, pp. 100-111).
p. 197
a certain degree of sloppiness: Darwinian natural selection is
predicated on a certain degree of random variation in the characteristics of
individuals, which leads to competition and selection. Maynard-Smith and
Szathmáry (1999, p. 7) state: “Since, almost inevitably, one cycle would be
more efficient in utilizing resources of the environment than the other, one
would be ‘naturally selected.’”
p. 198
“That’s for the chemists . . .”: As quoted by Harold Morowitz to
RMH, ca. 2001. This attitude prompted John Maynard-Smith to refer to
Kauffman’s work as “fact-free science” (Davies 1999, p. 141).
p. 199
An unbroken chemical history: The principle of continuity—
or congruity, as some call it—must apply to any origin-of-life scenario. Each
increase in emergent complexity must arise in an unbroken sequence from
the chemical processes of previous steps.
p. 199
The Protenoid World: Fox and Harada (1958), Fox and Dose
(1977), and Fox (1956, 1960, 1965, 1968, 1980, 1984, 1988).
p. 199
“Fox,” Morgan would often remark: As quoted in Dick and
Strick (2004, p. 40).
p. 200
Fox’s career thrived: Dick and Strick (2004, pp. 31-43), recount
Fox’s career and detail NASA’s grant support of his work commencing in
1960.
p. 200
“alive in some . . .”: Dick and Strick (2004, p. 41).
p. 200
As early as 1959: S. L. Miller and Urey (1959b). This reply was
in response to a letter by Fox (1959).
p. 201
Protenoid World was influential: For objective analyses of
Fox’s influence, see Fry (2000, pp. 83-88) and Dick and Strick (2004, pp. 31-
43). Fry concludes, “Though major parts of Fox’s theory were later chal-
lenged by many researchers, his influence at the time was instrumental in
turning the problem of the origin of life into a scientific subject.” (p. 88)
p. 201
nonrandom and deterministic: Following the Miller–Urey ex-
NOTES
281
periments, the prevailing attitude favored models of origins by random
chemical processes (Wald 1954).
p. 201
marginalized: Wills and Bada (2000, pp. 52-55) recount the
Fox story: “Over time, he became more and more of a maverick in the field.
Sadly, at the Eleventh International Conference on the Origin of Life, held in
Orleans, France, in 1996, he was reduced to having placards of protenoid
microspheres paraded around in the manner of a cartoon sandwich man
predicting the Second Coming.” (p. 55)
p. 201
The Thioester World: Christian de Duve’s hypothesis is articu-
lated in a series of books and articles, including an accessible presentation
for general readers, Vital Dust: Life as a Cosmic Imperative (de Duve 1995a).
See also de Duve (1991, 1995b).
p. 202
a “volcanic setting”: de Duve (1995b, p. 435).
p. 202
carbon–sulfur bond: de Duve (1995a, 1995b) notes that the
energy of the carbon–sulfur bond in thioesters is comparable to that of the
phosphate bond in modern energy-rich molecules such as ATP. De Duve
selects thioesters in his model because they are more plausible prebiotic
molecules from a geochemical perspective.
p. 202
steady supply: Some experimental evidence supports the as-
sumption of a steady supply of thioesters. Huber and Wächtershäuser (1997)
produced thioesters of acetic acid in experiments that mimicked hydrother-
mal conditions, while Weber (1995) described the production of amino acid
thioesters under similar conditions.
15
THE IRON–SULFUR WORLD
p. 205
“You don’t mind . . .”: Günter Wächtershäuser as quoted in
Radetsky (1998, p. 36).
p. 205
Günter Wächtershäuser’s: His theory is detailed in a series of
papers, including Wächtershäuser (1988a, 1988b, 1990a, 1990b, 1991, 1992,
1993, 1994, 1997). For a comprehensive overview of Wächtershäuser’s
chemical ideas, along with those of other advocates of sulfide-driven prebi-
otic processes, see Cody (2004).
p. 205
The contrast between heterotrophic and autotrophic: For dis-
cussions of the heterotroph-first versus autotroph-first debate, see Lazcano
and Miller (1996), Lahav (1999), Wills and Bada (2000), and E. Smith and
Morowitz (2004). Note that the autotroph-first position is also, by necessity,
deterministic; and it represents a metabolism-first viewpoint.
A measure of the relative complexity of autotrophs and heterotrophs is
provided by the minimum number of genes required for cells to survive.
Morowitz et al. (2004) estimate that heterotrophic cells, which obtain all
282
GENESIS
essential molecules from their surroundings, require a minimum of approxi-
mately 500 genes. By contrast, modern autotrophic cells require at least 1,500
genes. This sharp contrast in genomic complexity is perhaps the strongest
argument in favor of a heterotrophic origin.
p. 206
irrelevant to the origin of life: Wächtershäuser (1988b, p. 453)
states the case: “My theory contrasts sharply with the ingenious prebiotic
broth theory of Darwin, Oparin, and Haldane for I deny the preexistence of
any arsenal of organic building blocks for life (such as amino acids). Rather,
I assume the concentration of dissolved organic constituents in the water
phase is negligible.”
pp. 206-207
precious little evidence: A number of theoretical studies,
notably by Everett Shock (then at Washington University in St. Louis), lent
support to the idea of hydrothermal organic synthesis in general, if not the
Iron–Sulfur World hypothesis in detail (e.g., Shock 1990a, 1990b, 1992a,
1992b, 1993; and Shock et al. 1995). Shock (now a professor at Arizona State
University) and his students use thermodynamic models based on the rela-
tive energies of chemical products and reactants. They demonstrate that the
inherent lack of equilibrium between oxygen-poor hydrothermal fluids and
more oxidized seawater can drive metabolism and the formation of carbon–
carbon bonds. For example, Shock et al. (1995, p. 141) write, “The amount
of energy available was more than enough for organic synthesis from CO or
2
CO, and/or polymer formation, indicating that the vicinity of hydrothermal
systems at the sea floor was an ideal location for the emergence of the first
chemolithoautotrophic metabolic systems.” (A “chemolithoautotroph” is an
autotroph that gets its energy from the chemical disequilibrium of miner-
als.) Our experimental group was greatly influenced by Shock’s efforts, and
for a time he was a NASA Astrobiology Institute co-investigator with the
Carnegie Institution team. By contrast, Wächtershäuser, whose publications
are typically characterized by copious references to other work, has rarely
cited Shock’s papers.
p. 207
the initial tests: Drobner et al. (1990). A key aspect of this ex-
periment was the exclusion of any oxygen, which might have poisoned the
reaction by forming iron oxides. Hence, they describe “the formation of both
pyrite and molecular hydrogen under fastidiously anaerobic conditions in
the aqueous system of FeS and H S” (p. 742). See also Blöchl et al. (1992).
2
This group also studied amino acid polymerization (Keller et al. 1994).
p. 207
Wolgang Heinen and Anne Marie Lau
wers: Heinen and
Lauwers (1996).
p. 207
Subsequent experiments: Huber and Wächtershäuser (1997,
1998) and Huber et al. (2003).
p. 207
Our research group: Cody et al. (2000, 2004). See also the com-
mentary by Wächtershäuser (2000).
NOTES
283
p. 208
The Reverse Citric Acid Cycle: Wächtershäuser (e.g., 1992, pp.
129 et seq.) proposes that the reductive citric acid cycle is the basis for the
first autocatalytic cycle. Harold Morowitz has elaborated on this idea
(Morowitz et al. 2000, Smith and Morowitz 2004). Others are not persuaded,
however. Orgel (1998a, p. 495) notes that in the absence of enzymes, “the
chance of closing a cycle of reactions as complicated as the reverse citric acid
cycle, for example, is negligible.”
As one possible counterargument, Harold Morowitz now advocates the
role of “small molecule catalysts” such as the amino acid proline, “which can
act as a catalyst in aldol condensations. Small molecule catalysis can then act
as a self-organizing principle in forming metabolic networks.” [Quoted from
an announcement of Morowitz’s lecture, “A Principle of Biochemical Orga-
nization: The Roots of Genetic Code Within the Intermediary Metabolism
of Autotrophs,” delivered at the Krasnow Institute for Advanced Study,
George Mason University, 13 September 2004]
p. 208
a simple philosophy: These ideas are detailed in Morowitz
(1992), in which he argues that “Metabolism recapitulates biogenesis.”
p. 208
In the mid-1960s: Evans et al. (1966).
p. 209
At a recent seminar: Morowitz’s seminar entitled “The Feed-
Down Principle” was delivered at the Krasnow Institute for Advanced Study,
George Mason University, on February 2, 2004. His theme (from the ab-
stract): “Biology appears to be organized in a hierarchical fashion with a
biochemical core consisting of the tricarboxylic acid cycle (TCA cycle or
reductive TCA cycle) and the reaction network producing all of the key bio-
chemical building blocks.”
p. 210
modern metabolic enzymes: See, for example, Adams (1992)
and Beinert et al. (1997).
p. 210
formation of pyrite: In Wächtershäuser’s Iron–Sulfur World,
the mineral pyrite plays a crucial role as the solid surface to which life clings.
Under many geochemical conditions, pyrite has a positively charged surface,
whereas the essential compounds in the reductive citric acid cycle are negatively charged molecules. The metabolic molecules thus bond strongly to