INTERPLAY BETWEEN RAPID AND SLOW QUENCHINGIN PREBIOTIC EVOLUTION
Koichiro Matsuno
Nagaoka University of Technology
Nagaoka 940-2188, Japan
E-mail: CXQ02365@nifty.com(Received November 17, 2008; Accepted December 24, 2008)
in vials from Miller’s other experiments [2], though
not reported previously, reveals that when an
aspirating nozzle from which a jet of steam and gas
was injected into the spark chamber was further
attached to the water-containing flask, 22 different
kinds of amino acid and five amines were identified.
This result makes a marked contrast to the original
result Miller reported, especially in the respect of theenhanced diversity of the products. Use of anaspirator or an orifice can more explicitly signify theact of adiabatic expansion which is in turn aptly
capable of inducing adiabatic cooling or rapid
quenching [3].
Functional competence of rapid quenching in thesimulated prebiotic evolution is widespread andubiquitous [4-8]. Nonetheless, one methodologicallimitation remains inescapable in the framework ofexperiments in the laboratory. Implementing theprocess of quenching requires at least two separate
heat reservoirs at different temperatures. The
products whose synthesis is activated by the heat
energy available from the reservoir at the higher
temperature can be quenched and stabilized when
they suddenly come to contact with another reservoir
at the lower temperature. In fact, preparing two heat
reservoirs at different temperatures is technicallyfeasible in the laboratory. However, once thedecomposition of the synthesized products comes tobe focused upon, participation of a third heat
reservoir whose temperature is further lower thanthose of the former two would have to be called for.
Otherwise the proper continuous operation ofprebiotic evolution would be jeopardized because of
facing the stalemate frozen in the form ofstabilization of the synthesized products.
We shall then try to see how the three different
kinds of heat reservoir at three different temperatures
could be implemented in the natural setting so as tokeep the natural operation of prebiotic evolution
sustainable.

(Abstract)
Prebiotic evolution on the primitive Earthcould have proceeded through the interplay between
the two modes of quenching, rapid and slow, of thesynthesized products. The rapid quenching
instrumental to stabilizing the synthesized products
occurring near the surface of the Earth materializes as
traversing from the high temperature specific to theenergy source driving synthetic reactions, such as thephotons from the sun or the magmatic heat from thecore mantle of the Earth, to the normal ambient
temperature near the surface. In contrast, the slow
quenching as a necessary vehicle for disintegrating
the synthesized products into the raw materials forthe subsequent synthetic reactions to successively
follow materializes as traversing from the normal
ambient temperature near the surface of the Earth tothe extremely low temperature characterizing deep
outer space. A means of reaching out to deep outerspace from the Earth is through the emission of the
microwave photons. The microwave photons can beemitted in the process of orientational polarization ofelectric dipole moments intrinsic to the synthesizedoligomeric products.
(Keywords)
cosmic microwave background; dielectric dipole;heat reservoirs; hot vents; outer space; quenching
1. Introduction
Chemical evolution is cosmological in its scale.
When an inter-stellar dust particle is irradiated by aultra-violet photon emitted from a remote star, theparticle would suddenly be warmed up and start
synthetic reactions among the small molecules, suchas methane, nitrogen, carbon mono-oxide and wateramong others, adhered on its surface. The
synthesized products including the precursors ofamino acid molecule could then be stabilized throughthe rapid quenching due to the subsequent directcontact with deep outer space. The temperature ofdeep outer space to be measured as referring to themicrowave spectrum is about 2.725K imputed to thecosmic microwave background if the inter-stellar
cloud nearby is not dense enough.
Heating up of the reactants and the subsequent
rapid quenching of the synthesized products in thecosmological scale are quite suggestive toexperimental studies on simulating prebiotic
synthesis proceeding on the primitive Earth (e.g., see
the appendix in Japanese). Miller’s gas discharge
experiment [1] was equipped with both energy supply
in the form of gas discharge and rapid quenching of
the effluent products in the attached condenser. Whatis more, recent re-examination of the products saved

Viva Origino 37 (2009) 1-6ⓒ 2009 by SSOEL Japan

2. Slow Quenching
Sustainable prebiotic evolution could proceed
through the interplay between the synthesis and thedecomposition of oligomeric products. Nonetheless,if the time scale of each synthetic reaction happens to
be of the same order of that of each decomposition
reaction, the whole combined set of the two sorts ofreaction could eventually reach an apparent stationary
condition and could not be evolutionary any more
over the long time span which is far greater than thetime scale measuring each reaction. If the interplay
between the synthesis and the decomposition turnsout evolutionary altogether by all means, on the other
hand, the time scale characterizing the decomposition-1-Viva Origino 37 (2009) 1-6
evolution could thus be seen to undergo an extremely
slow quenching as releasing the stored energy in theform of the microwave photons. The next question
coming up would be how prebiotic evolution could
naturally implement such a decomposition scheme
accompanied with emission of the microwave
photons.

would have to be far greater than the time scale forthe synthesis if the latter remains fixed. A large
difference between two time scales, for synthesis andfor decomposition, can let the underlying reactions be
evolutionary in avoiding easy access to stationary
stalemates.
This observation then raises a serious question onwhether and how, if ever possible, the time scalecharacterizing the decomposition reactions could turnout far greater than the time scale measuring thesynthetic reactions.
Indicative to the extraordinary enhancement of thetime scale of the decomposition reactions on the basisof factual observation is an enzymatic reaction met in
the practice of biochemistry. Take, for instance, an
ATP hydrolysis with the help of a myosin molecule
serving as an ATPase enzyme. A myosin molecule
helps hydrolyzing an ATP molecule and releasing theenergy of order of 30kJ/mol over 10 milli-seconds. If
energy release as much as 30kJ/mol by breaking asingle phosphate bond within an ATP molecule takes
place as emitting a single photon, the energy of thephoton could roughly be of order of 5×10-20J and its
emission would be completed within 10-14s. However,
the actual energy release takes as long as 10 milliseconds. Such an enormous elongation of the timescale for an ATP hydrolysis is equivalent to releasing
the energy of 5×10-20J by emitting a train of many
low-energy photons. If the emission of those lowenergy photons over 10 milli-seconds is uniform in acontinuous fashion, each photon would turn out tocarry energy as much as 10-26J and the total numberof the low-energy photons emitted over 10 milliseconds would reach about 106. The frequency ofeach emitted photon could be about 100MHz in the
microwave range [9, 10].
The present survey, though specific to the alreadyfully developed biological organisms, is quite
suggestive in calling our attention to a possible
scheme of enhancing the time scale of decomposition
reactions in prebiotic evolution. A key at this point is
a possibility of emitting the microwave photons in
the process of decomposition reactions.
Once the prebiotic synthesis of oligopeptides withuse of rapid quenching is focused upon, it could be
likely to encounter participation of polar amino acids,
such as aspartic acid, glutamic acid, arginine andlysine, in the oligomerization process. A polar aminoacid in a synthesized oligopeptide then maintains apermanent electric dipole moment, and the resulting
oligopeptide is electrically polarized. When thepolarized oligopeptide is mechanically disturbed
from its outside, it tends to be stabilized through theadjustment of the orientational polarization of theoligomer. Since the movement of the orientationalpolarization is associated with the acceleration ofelectrically charged particles in the oligomer, it canradiate an electromagnetic wave as a matter ofprinciple.
Furthermore, the characteristic frequency for theorientational polarization of oligo- or polypeptide canbe found in the frequency range of 100MHz∼10GHz[11]. Oligopeptides to be synthesized in prebiotic

3.

Three-Staged Heat Reservoirs
As a matter of principle, a role of heat reservoirs to
be involved in prebiotic evolution can be evaluated interms of the energy flux density from each source[12]. The density of the solar energy flux impinging
on the surface of the Earth or the solar constant isabout 1370W/m2. Although the flux density on thesurface of the sun maintained at temperature 6000K
is estimated about 2.4×106W/m2 based upon Planck’s
law of black body radiation, the density of theimpinging solar photons on the Earth is significantly
diminished while the energy of each solar photon
remains unchanged during the flight from the sun to
the Earth. In contrast, the ambient temperature 290K
near the surface of the Earth gives the thermal energy
flux density of roughly 20W/m2, which should becontrasted to the basal metabolic rate of 30W/m2 ofan average organism living on the Earth. The presentrough coincidence between the energy flux densityfrom the black body radiation and the basal metabolic
rate of an average organism, though their origins aretotally different, would make the surface of the Eartha habitable zone to the organism in the hindsight.
Underlying the coincidence is the slow
decomposition of the products synthesized as being
subject to the energy influx of 1370W/m2 while
experiencing, at the same time, the thermal energy
flux density specific to the ambient only as much as
20∼30W/m2.
In a similar vein, the thermal energy flux density inthe hot spring at, say, 573K or 300oC, nearhydrothermal vents in the ocean is about 170W/m2,
while the cold surrounding water maintained at 273K
or 0oC keeps the nearby energy flux density on thelevel of 10W/m2. The rapid quenching from theenergy flux density 170W/m2 near hot vents to
10W/m2 in the immediate neighborhood of the cold
surrounding water could be instrumental to various
synthetic reactions as freezing the former thermalenergy into the binding energy of various chemicalbonds. In addition, the slow decomposition of the
products synthesized in the process of rapid
quenching would take place as experiencing thethermal environment allowing for the thermal flux
density of 10W/m2.
The likelihood of slow decomposition of thesynthesized products, which may be indispensible forboth prebiotic and biotic evolution, now comes toface a serious challenge. In any case, thermodynamic
constraints are inescapable. The temporary
stabilization of the evolving products to besynthesized and their slow decomposition cannot
proceed as experiencing one and the sameenvironment in thermal equilibrium, in the latter ofwhich there is no likelihood of evolution. The slow

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Viva Origino 37 (2009) 1-6
temperature without offending thermodynamic
principles. Prebiotic synthesis is found to proceed
through the operation of at least two different kindsof heat engine implemented in a tandem manner. One
is to operate between the higher temperature uniqueto the energy sources for driving synthetic reactions
and the normal lower temperature characterizing theambient for the temporary stabilization of thesynthesized products. Another one is between thenormal ambient temperature and the extremely low
temperature intrinsic to the cosmic microwave
transparency for supporting the slow decompositionof the synthesized products. The environment near
the surface of the Earth maintained at the normal
ambient temperature serves as the low temperature
heat reservoir for the prebiotic synthetic reactions,while it also serves as the high temperature heat
reservoir for the slow decomposition of thesynthesized products.

decomposition requires one more heat reservoir, in
addition to the reservoir at a higher temperaturedriving various synthetic reactions and another one at
the normal ambient temperature for saving andstabilizing the synthesized products at least
temporarily. The third reservoir must be the one
being capable of absorbing the microwave photons of
their frequency around 100MHz. As a matter of fact,
the black body radiation whose peak frequency isaround 100MHz is to maintain its temperature as low
as 1 milli-Kelvin.
An empirical likelihood of the heat reservoir that
can absorb the microwave radiations is in fact
guaranteed by the present big-bang cosmology.
Although deep outer space is filled with the cosmic
microwave background whose black-body radiationis centered around its frequency 100GHz or at
2.725K in terms of the black-body radiation
temperature, it is quite transparent to the microwaves
whose frequency is far less than 100GHz. Deep outerspace can serve as a heat reservoir maintained at anextremely low temperature even compared to 2.725K
due to the cosmic microwave background, and it canbe reached out by means of the emission of the
microwave photons even from the surface of the
Earth.
The cosmic microwave transparency being
infinitely absorptive towards the microwave disposals
without suffering the risk of being struck back on thepart of the emitter now function as the third heat
reservoir positioned at an extremely low temperature[13]. Such a natural implementation of the heat
reservoir maintained at an extremely low temperature
can make the slow decomposition of the synthesized
products proceeding in the normal thermal
environment, thermodynamically comprehensible.
When one considers the slow decomposition as
following the scheme of a heat engine operating
between the normal ambient temperature and theextremely low temperature characterizing the cosmic
microwave transparency, the efficiency of the work
to be done by processing the transfer of heat energy
would approach almost unity because of the extreme
smallness of the lower temperature. Most of the heat
energy fed from the heat reservoir at the higher
temperature can be transferred into work. The relative
amount of the heat energy transferred into the heat
reservoir maintained at the extremely low
temperature in the form of the microwave photons
directly reaching out to deep outer space could beminute, though substantial at the same time,compared to the one transformed into various modesof work, the latter of which could eventually bedissipated as heat energy into the normal thermal
environment.
The present minute, nonetheless indispensible,
amount of energy flow in the form of the microwave
photons, directly reaching out to deep outer space,can thus provide a solid physical means for an almost
complete coincidence of both the temporary
stabilization of the synthesized products and theirslow decomposition in sharing the one and the same
thermal environment maintained at the normal

4.

Prebiotic Enzymatic Reactions
Actual implementation of three-staged heat
reservoirs could be made feasible even in prebiotic
evolution if some oligomers functioning like an
enzyme appear in a prebiotic synthesis. An
experimental candidate for suggesting the emergenceof a prebiotic enzyme can be seen in the synthesis ofoligopeptides in the solution of even only glycine andalanine in the flow reactor simulating a submarinehydrothermal system [14, 15]. We observed thebuildup of glycylalanine followed then by thesynthesis of alanylglycine while dissecting the preexisting glycylalanine. The sequence of emergence
was always glycylalanine first and then followed byalanylglycine, and by no means vice versa.
Alternation of glycylalanine by alanylglycine goingalong with dissecting glycylalanine suggests
participation of enzymatic oligomers being capable ofdissecting glycylalanine. A likelihood of such
enzymatic oligomers to emerge could be seen in thewide variety of oligopeptides available in the flow
reactor experiment.
The synthesis of glycylalanine is endergonic infreezing some of the heat energy supplied from theheat source maintained at a high temperature into theform of peptide bond, while the decomposition of thesynthesized glycylalanine is exergonic in releasing
the stored energy. The involved enzymatic reaction
could change the molecular configuration of thesubstrate through the tactile interaction which may be
extremely slow compared to electronic movements as
being epitomized in the mechanical adjustment of a
key-lock relation. More specifically, the ongoingtactile interaction can mechanically disturb the
directional movement of electric dipole moments
latent in the participating oligopeptides. Oligomers
made of glycine and alanine can in fact maintain in
their inside electric dipole moments even though bothamino acids are non-polar, since the electric charge
distribution is not uniform along the peptide chain.
Consequently, the tactile deformation of the substratecaused by the thermal disturbances expected at thenormal ambient temperature could be reacted upon-3-

Viva Origino 37 (2009) 1-6
5. Imai, E., Honda, H., Hatori, K., Brack, A. and Matsuno,
K. Elongation of oligopeptides in a simulated
submarine hydrothermal system. Science 283, 831-833(1999).
6. Imai, E., Honda, H., Hatori, K. and Matsuno, K.
Autocatalytic synthesis of oligoglycine in a simulated
submarine hydrothermal system. Origins Life Evol.
Biospheres 29, 249-259 (1999).
7. Islam, M. N., Kaneko, T. and Kobayashi, K. Reactionof amino acids in a supercritical water-flow reactor
simulating submarine hydrothermal systems. Bull.
Chem. Soc. Jpn 76, 1171-1178 (2003).
8. Nemoto, A., Ikeya, R., Imai, E., Honda, H. and Matsuno,
K. A clue for prebiotic conversion of carboxylic acids
and its evolutionary relevance to the TCA cycle. Viva
Origino 34, 90-95 (2006).
9. Matsuno, K. Being free from ceteris-paribus - a vehicle
for founding physics upon biology rather than the otherway around. Appl. Math. Comp. 56, 261-279 (1993).
10. Matsuno, K. Cell motility as an entangled quantum
coherence. BioSystems 51, 15-19 (1999).
11. Kao, K.- C. Dielectric Phenomena in Solids: With
Emphasis on Physical Concepts of Electronic
Properties. Academic Press, New York (2004).
12. Chaisson, E. The cosmic environment for the growthof complexity. BioSystems 46, 13-19 (1998).
13. Matsuno, K.
Molecular semiotics toward theemergence of life. Biosemiotics 1, 131-144 (2008).
14. Ogata, Y., Imai, E., Honda, H., Hatori, K. and Matsuno,
K. Hydrothermal circulation of seawater through hotvents and contribution of interface chemistry toprebiotic synthesis. Origins Life Evol. Biospheres 30,
527-537 (2000).
15. Yokoyama, S., Koyama, A., Nemoto, A., Honda, H.,
Imai, E., Hatori, K. and Matsuno, K. Amplification ofdiverse catalytic properties of evolving molecules in asimulated hydrothermal environment. Origins Life
Evol. Biospheres 33, 589-595 (2003).

by emitting a train of the microwave photons. Theenergy source compensating for the emission of the
microwave photons could be attributed to theexergonic reaction for dissecting the synthesizedoligomers.
5.

Concluding Remarks
Prebiotic evolution proceeding on primitive planets
including the primitive Earth requires both the energy
sources and sinks as its necessary ingredients.
Chemical synthesis of oligomers from the smallerorganic molecules in the primitive environments on
the Earth could be endergonic as being fed by either
the photon energy from the sun or the heat energy
from the core mantle of the Earth. The synthesizedoligomers can freeze and store the supplied energy
internally in the form of chemical bonds through theprocess of rapid quenching. Sustainable chemical
evolution could then be made possible by constantly
disintegrating and converting the synthesizedoligomers into the smaller molecules to be taken in
again as the necessary material resources for thesubsequent synthetic reactions in an alternatingmanner. Such disintegration reaction is exergonic as
releasing the energy acquired in the preceding
synthetic reactions, extremely slowly.
The slow quenching characterizing such exergonic
reactions makes the thermodynamic framework
available to the likelihood of prebiotic evolution
proceeding near the surface of the Earth maintainedat temperature roughly 290K, to be multi-staged or atleast three-staged. The effective temperature of theenergy source driving the endergonic reactions is far
high above 290K while the accompanied heat sink forstabilizing the synthesized products is maintainednear at 290K. In contrast, the temperature of theenergy source driving the exergonic reactions is nearat 290K while the temperature of the intended heatsink for the disintegration reactions must be far
below 290K. The candidate of the lower temperature
heat sink is deep outer space itself, and the means oftaking advantage of and reaching out to the sink is
the microwave photons to be emitted in the processof the intervening disintegration reactions. The
prebiotic material vehicle for reaching out to deep
outer space maintained at an extremely low
temperature could be the emission of the microwave
photons from dielectrically polarizable oligomers that
can also function as prebiotic enzymes.

Appendix
起原にかかわる実験で可能なこと‐なにが問題なのか？‐
生命の起原を積極的に意識した化学実験はオパーリンに端を発します。その流れに沿って現れた画期的な成果が、1953 年に報告されたミラ
ー、ユーリーによる還元性大気での放電実験です。アミノ酸の生成が確認されました。それから半世紀あまりを経て現在に至っております。
その間、ミラー・ユーリーの枠組みに従って多彩な成果が生み出されてきました。しかし、判明してきたのは、目指す起原がますます遠のいて行った、とする皮肉な事態です。このことは、相反する二つのことを示唆します。一つは、起原はわれわれの手に負えるような代物ではない、とする覚めた悲観論です。もう一つは、現在に至るまでの半世紀の間、賢明かつ真面目に起原を手中に収めようと多数の関係者が心がけながら、心ならずも的をはずしてきたのではないか、との反省に基づく楽観論です。ここで、私がお話しようと思うのは、この楽観論の方です。
生命の起原を目指した化学実験は手段としてはまともであり、それに対抗できる新たな手段を思い浮かべることは困難です。コンピュータとそのディスプレーは強力な武器でありながら、それが有効となるのはあくまでも、ある程度的が絞り込まれてからです。求められているのは、漠とした起原の問題を技術的に処置可能な問題にまで絞り込むことです。少なくともわれわれの原始地球は、当初さまざまな漠とした問題をReferences
1. Miller, S. L. A production of amino acids underpossible primitive Earth conditions. Science 117, 528529 (1953).
2. Johnson, A. P., Cleaves, H. J., Dworkin, J. P., Glavin,
D. P., Lazcano, A. and Bada, J. L. The Miller volcanic
spark discharge experiment. Science 322, 404-404(2008).
3. Futamura, Y., Fujioka, K. and Yamamoto, K.
Hydrothermal treatment of glycine and adiabatic
expansion cooling: Implications for prebiotic synthesisof biopolymers. J. Mat. Sci. 43, 2442-2446 (2008).
4. Matsuno, K. A design principle of a flow reactor
simulating prebiotic evolution. Viva Origino 25, 191-204(1997).

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Viva Origino 37 (2009) 1-6
かかえ込みながら、その一部を生命の出現という仕方で問題を絞りこむことに成功してきました。実験科学者としてのわれわれもそれにあや
かりたく思っています。ここで、状況が少し明らかになってきます。起原を取り巻く問題とは一体どのような種類の問題であって、それを解決可能な問題にまで絞り込むための技術的手段に、なにがあったのか、との状況分析が、関心を寄せるに足る的として浮かびあがってきます。
起原を特徴づける現象は持続する化学反応の出現です。原始地球上を想定したとき、反応分子とその反応を駆動するエネルギー源がなんであったか、については凡そ目安が立ちます。エ
ネルギー源を担うのは原子核の分裂、あるいは核融合反応であって、地熱、太陽光あるいは宇宙線を介してエネルギーが反応分子に提供されます。その原始地球を巨大な一つの化学反応炉とみなしたとき、そこで発生することになる厄介な問題に次の二つがあります。反応分子が十分に用意されていながら、反応を駆動するエネ
ルギーが欠けているのがそのひとつ目です。もう一つの問題は、エネルギーが十分に用意されていながら、反応分子を欠いている場合です。
この二つが問題になるのは、いずれの場合も極めて不安定だからです。反応分子が用意されていながらエネルギーを欠いている場合には、エネルギーがわずかでも外から新たに加えられると、新たな反応が進行します。また、エネルギーが用意されていながら反応分子を欠いている
場合には、反応分子がわずかでも外から新たに加えられると、同じく新たな反応が進行します。
この巨大化学反応炉が熱平衡にあれば、エネル
ギーと反応分子の間に安定した平衡状態が期待されますが、原始地球を取り巻く巨大化学反応
炉は決して熱平衡に達してはいません。
エネルギーと反応分子との間で安定した釣り合いを欠いたまま化学反応炉の運転が開始されたとき、どのような道筋を経て、比較的安定した運転状況に移り行くことができるのか？これが、化学反応炉としての原始地球の遭遇した問題であったはずです。この比較的安定した運転状況のうちに含まれるのが、生命の出現と呼ばれる現象です。生命の出現が比較的安定した現象である、との表明には二重の意味がこめられています。比較的安定であるとは、外部から少々の揺さぶりを受けてもそれに動じない頑健さを備えている、ということです。この頑健さがなければ、生命の出現にあたかも敵対するかのような苛酷な周囲状況のなかからその出現を期待することは甚だしい的はずれになります。
さらに、生命の出現がまったくの気まぐれによるものとするならば、その出現を実験科学の対象にするのはそれこそ正気の沙汰ではなくなります。
そこで巨大化学反応炉としての原始地球に提供されたと思われる反応分子とエネルギーの素性を、もう少し具体的に見てみることにします。
反応分子としては、アミノ酸分子を例としてとりあげます。エネルギー源としては原始海洋での熱水口近傍で利用可能となる熱エネルギーを考えてみます。熱水口からの熱エネルギーはその近くのアミノ酸の重合を促進します。しかし水中の重合反応であるため、加水分解も同時に-5-生じます。この中にあって、利用済み熱エネル
ギーは周りの冷海水中に廃棄されます。ここで進行する熱重合反応と加水分解反応には、熱平
衡反応において認めることのできない、一つの特徴が備わっているのがわかります。重合反応の各々がそれとは逆方向に進む分解反応と個別に釣り合っていることはない、とする特徴です。
この個別反応での釣り合いの欠如は、熱平衡反応では決して想定することのできなかった状況です。
熱平衡系では、定義により、順方向に進む反応は、それぞれ、それを反転させた逆方向に進む反応と個別に釣り合う、との詳細釣り合いが成立しています。この詳細釣り合いを熱水口近傍での反応には適用することができません。わ
れわれは実験によってこのことを実際に確かめました。熱平衡ではアミノ酸モノマーの重合によってダイマーが生じる反応は必ずダイマーがモノマーに分解する反応と釣り合い、それによって熱平衡反応の安定性が保たれています。ところが熱水口近傍での反応では、モノマーの重合によってダイマーが生成され、そのダイマーが新たなモノマーと重合してトライマーを生成し、そのトライマーがさらに新たなモノマーと重合してテトラマーを生成し、そのテトラマーが加水分解を受けて二つのダイマーに分解される経路があることがわかりました。化学反応系
が比較的安定に実現するためには、重合と分解の釣り合いが求められながら、ここで実現したのは熱平衡系を想定した詳細釣り合いではなく、迂回路を経由した迂回路釣り合いです。ダイマーの安定性を評価するには、それと直結したモ
ノマー、トライマーとの反応に加えて、テトラマーからダイマーに戻る迂回路経由分も加える
必要がでてきます。
熱水口近傍では、迂回路釣り合いを介してそこでの化学反応系の安定性を実現するものがあります。このことが実験によって確認されました。迂回路釣り合いによる、安定した化学反応
系の実現とは、安定した化学反応回路に実現に他なりません。加えて、ひとたび、化学反応回路が実現されますと、それを特徴づける一つの定量的な指標が登場してきます。化学反応経路の下流から上流に向けての還流があるため、その寄与は自己触媒的となり、回路を構成する分子は、ある限られた時間内ではありますが、時間の経過とともにその個数を指数関数的に増加させます。このことも、実験によって確かめる
ことができました。
要約します。熱水口近傍において化学反応回路を実現することが可能となります。これまで、安定した、自律的な化学反応回路の実現は生化
学の独壇場でした。ところが、実験という手段に訴えるならば、生物、あるいは生命の出現するはるか以前から、原始地球上の海洋中の熱水口近傍で比較的安定な仕方で、化学反応回路が出現し得た、とする見方が新たに浮かび上がってきます。物質現象としての生命の特徴は、それが保有する化学反応回路にあります。原始地
球がエネルギーと反応分子とをいかに釣り合わせるかとの問題を抱え、それを解決可能な問題に絞り込もうとしていたとき、熱水口由来の化学反応回路は得難い助け舟の一つになり得たは

Viva Origino 37 (2009) 1-6
ずです。仮に原始酵素の出現が偶然に由来するできごとであっても、それの定着を熱水口由来の、比較的安定した化学反応回路に委ねる、とする道がここに開かれてきます。原始酵素と化
学反応回路のいずれもが、特異的である、という点において共通しているからです。もちろん、お互いに助けにならなければ、それを参照する
必要は毛頭ありません。
生命の出現に向けて問題状況を絞り込むことができたとは、生命の出現以前に既に自然選択が働いていた、ということです。複製分子が出現する以前でも、自然由来の選択は可能です。
海底熱水口の近くでは確かに、前生物的自然選
択が可能となる一つの条件を満足しています。
高温で重合した反応物が周りの冷海水に抛り出され、それが分解される以前に急冷されますと、分解の抑制により、重合の方が熱平衡での反応に比較して選択的に、かつ一方的に強調されることになります。さらに、熱水口を繰り返し訪れることにより、この選択性の寄与は掛け算の仕方でその効果を拡大して行きます。原始地球にとっての海底熱水口は、そこで進行する化学
進化に、前生物的自然選択の場を提供した、となります。化学反応回路の出現は、前生物段階
での自然選択が働いた一例です。
この前生物的自然選択は、分割することのできない資源の消費を司る法則、たとえば、ポテ-6-

ンシャルとしての温度差に対するフーリエの熱伝達則や電位差に対するオームの法則の内に、すでに含まれています。資源は一方的に消費される対象であるため、それを貫くのは、独り占めによる早もの勝ち、の原則です。資源の消費を司るのは消費者であり、消費者の中で支配的になるのは消費速度を最大とするものです。ある一定の消費速度を伴った消費者の中により小さな速度で消費するものが現われても消費者の交代は起こりません。しかし、より大きな速度で消費するものが現われた場合には旧来のものに代わってそれが定着し、消費者の交代が生じます。フーリエの熱伝達則、あるいは、オームの法則が安定した物理法則であると信頼されているのは、最大速度での資源消費を保証する、
前生物的な自然選択のためです。
始めに、ミラー・ユーリーの枠組みの生産的な点とその限界について触れました。この枠組
みの歴史的な意義を認めた上で、さらに求められるのは、起原にかかわる問題の一層の絞り込です。その絞り込み先の候補として、ここで申し上げたく思っていたのが、生物あるいは生化学に由来しない化学反応回路の活用です。実験に基づくかぎり、原始海洋の海底熱水口近傍では、生命を前提とすることなく、化学反応回路の運転が可能となりえたはずです。