Journal of Modern Physics, 2011, 2, 602-614
doi:10.4236/jmp.2011.226070 Published Online June 2011 (
Copyright © 2011 SciRes. JMP
On the Origin of Biological Functions
Alexander Umantsev
Department of Chemistry/Physics, Fayetteville State University, Fayetteville, USA
Received February 9, 2011; revised March 23, 2011; accepted March 24, 2011
We consider the problem of structure and functions of the first forms of living matter and present a hypothe-
sis that they were formed through a physico-chemical process known as dendritic crystallization. According
to this hypothesis the branching, dendritic structures helped build living systems by lending them functions
so that organic chemical evolution is just one natural consequence of the evolution of matter in the universe.
We conclude that a self-replicating biological system with adaptation emerged from simple molecules using
completely abiotic mechanism of formation, which acted simultaneously or intermittently at different places
on the early Earth and created similar structures everywhere. The dendritic hypothesis of origin of the func-
tions explains similarities in the living systems and supports the assumption of a ‘second genesis of life’. The
dendritic scenario does not need carbon/phosphorus-based solutes in water-based solutions, which may have
important implications for exobiology and extraterrestrial origin-of-life scenarios. An experiment to test the
hypothesis is suggested.
Keywords: Origin of Biological Functions, Dendritic Growth, Prebiotic Chemistry, Protobiont
1. Introduction
Classification of tenable origin of life theories may be
based on different principles. Davies and McKay [1]
divided them into the categories of Extraterrestrial and
Terrestrial origins. Bada [2] classified the Terrestrial
theories into two categories “The prebiotic soup theory”
and “The metabolist theory” and tried to build a consen-
sus by incorporating them into a general scheme of “the
transition from abiotic organic compounds to autono-
mous self-replicating molecules capable of evolving by
natural selection into ones of increasing efficiency and
complexity …” The unified theory culminated in the
RNA World. Below I will review only works which are
essential for the present discussion and did not find a
way into the aforementioned reviews.
Prigogine and Nicolis [3] analyzed the problem of
presence of spatial order and functions in biological
structures and pointed to chemical evolution of matter in
the universe as a necessary prerequisite of life. They
concluded that “spatial dissipative structures”, attained
under nonequilibrium conditions in open systems, “have
contributed in an essential way to the first biogenetic
steps” and that emergence of biological order may be
seen as the “consequence of far from equilibrium ther-
modynamics applied to certain types of non-linear sys-
tems”. Prigogine [4] noted that the “dynamical instabili-
ties … are … at the root of complexity that is essential
for self-organization and the emergence of life”. Kauff-
man [5] introduced an origin-of-life hypothesis, which
assumes that the order of the first living systems was the
result of spontaneous self-organization, rather than of a
selection process. He also proposed that “Life is an ex-
pected, collectively self-organized property of catalytic
polymers” and suggested that it appeared as “a phase
transition leading to connected sequ ences of biochemical
transformations by which polymers and simpler building
blocks mutually catalyze their collective reproduction”.
Morowitz and Smith [6] introduced a hypothesis of “the
collapse to life” under the geological stress, which ex-
plains stability of the core biochemistry by using the
concept o f the phase transition between biotic and abiotic
Almost all workers writing about the origin of life had
at least some model of compartmentalization to over-
come the concentration gap problem, but the problem of
division persisted. Oparin [7] proposed a model of a
protocell based on the properties of a coacervate, a drop-
let composed of mixtures of colloidal particles formed by
the process of phase separation. He identified the
mechanisms of fragmentation and competition as neces-
Copyright © 2011 SciRes. JMP
sary for the protocell formation and growth. Morowitz et
al. [8,9] discussed “… the chemical logic of a minimum
protocell … as an entity thermodynamically separated
from the environment and able to replicate using avail-
able nutrient mo lecules and energy so urces”. They found
[8, p. 100] “a very real similarity between crystallization
and some aspects of self-replication”. The authors came
to the conclusion that the minimum protocell was a vesi-
cle of amphiphiles and chromophores. To explain divi-
sion of protocells they used Rashevsky’s [10] idea that
“at some point, the size of the membrane vesicle forming
the protocell increases to the point that stabilizing forces
are no longer able to maintain integrity, and the vesicle
breaks down into two or more smaller vesicles”. Unfor-
tunately, the authors had never presented the driving
force for such division, which is not trivial because the
surface energy of the vesicle drives the small ones to
coalesce into a large one that is, backwards. Recently
significan t progress was made in the area of sp ontaneous
growth and replication of fatty acid micelles and vesicles
with simple lipid membranes [11]. Hanczyc et al. [12]
showed that clay accelerates spontaneous formation of
vesicles of lipids. However, to induce vesicle division
the authors had to invoke the process of extrusion—
forceful drag of the material through a small-pore filter.
They admit that the “use of membrane extrusion to me-
diate division is artificial, and the possibility of a natural
analog of this process seems remote.” To inspire growth
and division of micelles and vesicles Rasmussen et al.
[13] used energy of light and Stano and Luisi [14]—the
surfactants. Although these results are impressive, it
should be realized that even simple fatty acids are com-
plicated materials for prebiotic conditions.
Based on an observation that natural minerals have
many of the properties of living organisms, e.g. crystals
can grow and store information in the form of crystal
defects, Cairns-Smith [15-17] put forth “the clay hy-
pothesis” of the mineral origins of life and the subse-
quent “genetic takeover”. He introduced the concept of a
genograph “as a kind of ‘picture’ of imperfections in a
crystal … that held … the primitive genetic information”
instead of a molecule. According to his hypothesis “A
mineral genetic material might hold information in the
form of a particular complex stacking sequences of lay-
ers and replicate it through an appropriate alteration of
growth and cleavage” [18]. Later on minerals (e.g. clay
or barium ferrite, Turner et al., [19]) become templates
for more complicated materials which “gradually ‘take-
over’ the control machinery” in the process of genetic
metamorphosis. In a “genetic staircase” scenario the
“multiple overlapping genetic takeovers” led to appear-
ance of sophisticated biological materials capable of their
own survival and propagation.
Chirality, as manifested by the preponderance of L-
amino acids and D-sugars in living matter, is another
property of life, which, together with the cellular org ani-
zation, should be addressed by the theories of life origin.
Kondepudi et al. [20,21] and Buhse et al. [22] demon-
strated the mechanism of spontaneous chiral symmetry
breaking (SCSB), where cooling and stirring of highly
concentrated aqueous solution of achiral molecules, e.g.
sodium chlorate, yields chiral crystals. This mechanism
involves random formation of a single crystal of arb itrary
chirality, from which ‘secondary crystals’ of the same
chirality were broken off by the external achiral process
of stirring and convection. This mechanism works only
in strongly supersaturated solutions (far-from-equilib-
rium). Viedma [23] added glass beads as the reinforce-
ment of stirring and was ab le to induce SCSB in slightly
supersaturated solutions (near-to-equilibrium). The ob-
vious problem of SCSB for the origin of life is that bio-
chirality is based on chiral mo lecules, not on chiral crys-
tals of achiral molecules. Hazen et al. [24-26] consid ered
the mechanism of chiral selectivity of mineral surfaces,
according to which equally represented chiral mineral
surfaces selectively adsorb chiral biomolecules, e.g.
amino acids or nucleotides, from racemic prebiotic soup.
SCSB mechanism may be used to describe the appear-
ance of the chirally adsorbing mineral environments out
of achiral geomaterial with the help of an external proc-
ess, e.g. convection in molten Earth, Earth’s magnetism,
or the Coriolis Effect. Yet, to achieve the biochemical
homochirality these mechanisms need a frozen accident
Shinitsky et al. [27] observed “unexpected difference
in the solubilities of D- and L-tyrosine in water, which
could be discerned by their rate of crystallization and the
resulting concentrations of their saturated solutions”.
This effect is neither due to the difference in D- and L-
equilibrium crystal structures, enantiomeric impurity,
surface of the vessel, nor due to secondary nucleation.
The authors conjectured that high cooperativity of crys-
tallization enhances minute difference of energies of the
enantiomers caused by the parity violation of weak nu-
clear forces. Based on this conjecture they suggested the
mechanism of the origin of biochirality: one enantiomer
was selectively removed from the racemic prebiotic soup
leaving behind a con centrated solution of the o ther enan-
tiomer; then biopolymerization took place in the leftover
solution, not in the crystal of the first enantiomer. Kojo
et al., [28,29] attempting to answer the question “Why
and how L-amino acids were selected in biosphere?”
found that “racemic D, L-asparagine induces asymmetric
resolution of co-existing racemic amino acids during
recrystallization”. Their data also show that crystalliza-
Copyright © 2011 SciRes. JMP
tion of racemic D, L-Asn yielded preferential formation
of L-crystals over D-crystals, the fact that was left unex-
plained. In essence, this is another manifestation of “un-
expected difference between D- and L-” enantiomers
discussed by Shinitsky et al. [27].
The fact that complex biochemical features are shared
by all forms of extant life made the origin-of-life scien-
tists assume that all organisms originated from the same
entity (single cell or a macromolecule), called Last Uni-
versal Common Ancestor (LUCA). However, recent ob-
servations and speculations forced many researchers to
reexamine this paradigm. For instance, careful analysis
of the geological records [30] shows that environmental
conditions conducive to the origin of life were intermit-
tent on early earth [31]. Wolfe-Simon et al. [32] found
that a bacterial strain can replace phosphorus in its key
macromolecules, including DNA, with arsenic. These
and other similar observations led researchers to an as-
sumption that “life may have arisen more than once” [33].
The hypothesis of the ‘second genesis of life’ becomes
even more important in the context of organic material
swap between the planets in the solar system [34].
2. Motivation
Almost all hypotheses of the origin of life on Earth de-
scribe the transformation from geochemistry to bio-
chemistry, which brought about the material of life, a
DNA-RNA-protein combination, and cellular organiza-
tion of that material. Living organisms, however, are
distinguished from a mixture of organic molecules by
their high level of complexity, which allows them to
carry out certain functions. Shapiro [35] pointed to a
“missing fragment in our picture of the origin of life … a
principle that governs the gradual evolution of simple
chemical systems into more sophisticated ones capable
of replication and Darwinian natural selection”. The
transition from a disorganized biomass to an organized
system capable of reproducing itself and adapting to
changing conditions represents the most puzzling prob-
lem in the study of the origin of life. The question of
‘Why did life adopt these particular functions?’ is left off
the discussion in these theories. They imply that the right
material will automatically take care of the functions
problem as soon as it appears, e.g. RNA molecules
‘know’ how to reproduce; a metabolist ‘knows’ how to
metabolize, etc. In fact, the question of the origin of the
functions may be separated from the question of the ori-
gin of the material; the biomolecules may even vary in
the make-up (e.g. Wolfe-Simon et al. [32]), but not in the
functionality. The question of the origin of the functions
deserves special attention and is the prime focus of the
present publication. In the Bada model [2], chance plays
a large role as the appearance of the first self-replicating
molecules, their functions, and some of their properties,
e.g. chirality, are assumed to come about by accident. If
the problem of origin of functions is not addressed, an
impression will remain that the extant form of life hap-
pened completely by accident, because other biomate-
rials are also possible. The problem of the origin of func-
tions gains additional significance in the context of exo-
biology because we may soon be dealing with new forms
of organic materials where silicon replaces carbon, arse-
nic—phosphorus, hydrogen-sulfide—water.
As pointed out above, in this article I am not con-
cerned with the question: which biopolymer came first—
protein or nucleic acid. Rather I am concerned with the
problem of the origin of functions of the living organ-
isms. Although the definition of functions of life is not a
trivial subject [36-39,94] most of the researchers in the
field agree that all biological (living) systems are char-
acterized by the following basic functions: growth and
metabolism, division and replication, mutation and evo-
lution [40]. Notice that not all apparent functions of life
are included into the list of the basic biological functions;
for instance, motility is not one of those.
3. Hypothesis
Many observations and speculations have led me to con-
clude that the life functions have their roots in the physi-
cal process of crystallization as opposed to a chemical
reaction. When crystallization in nonliving systems is
taking place far from equilibrium, it results in the forma-
tion of branching, dendritic, patterns which are also
ubiquitous and omnipresent in the biological systems.
Protobiont is a term that represents the first forms of
living matter [41,42]. Protobiont is a self-replicating
structure that carried some genetic information and could
multiply inside the complex primordial environments
e.g., slimy layers of molecules that had accumulated on
the rocks. According to the principle of continuity pos-
tulated by Morowitz et al. [8,9] the protobionts had to
have some of the biological functions, although enzymes
and macromolecules had not yet arisen. In many differ-
ent ways, protobionts are equivalent to Oparin’s coacer-
vates, Fox’s proteinoids [43], Orgel’s citroens [40], Wa-
chtershauser’s surface metabolists [44], Morowitz’s vesi-
cles of amphiphiles, Martin-Russell’s protocells [45],
Dawkins’ replicators [46], or Woese-Fox’s progenotes
[47]. However, in this paper I prefer to use the term pro-
I hypothesize that protobionts were formed through
the process of dendritic crystallization. The rest of this
article is an attempt to substantiate the hypothesis and
find useful applications of the latter. In this article I am
not attempting to pinpoint the material that underwent
the primordial crystallization, although a few candidates
Copyright © 2011 SciRes. JMP
will be suggested. I am trying to analyze the functional
relationships and show that dendritic structures possess
all characteristic functions of the living systems men-
tioned above.
Dendrites are branched microstructures of crystal
growth; they bring to mind pictures of snowflakes, see
Figure 1. Dendritic structure formation is an intrinsically
nonequilibrium thermodynamic transformation in an
open or closed system that occurs during crystallization
of many pure substances, including biologically impor-
tant ones, and their aqueous solutions [48-50, 51, p. 206].
Yet, not all crystals grow dendritically: dendrites appear
during crystallization of substances with low entropy of
fusion, Sf < 2kB, where kB is the Boltzmann’s constant
[52]. Dendritic morphology includes a primary stem,
secondary, tertiary, and sometimes even quaternary bran-
ches growing approximately in crystallographic direc-
Crystals grow from melts or solutions under certain
conditions becaus e they present thermodynamically more
favorable configurations in these conditions. For instance,
lowering temperature of the melt below the equilibrium
one makes it less favorable—contain greater amount of
the free energy—than the crystal of the same mass at the
same temperature, see Figure 2. In the process of phase
change, there will be a certain amount of heat and/or
species released. Crystals will grow only if the latent
heat and/or excess of species are removed from the
growing entity. To make this process the most efficient,
dendrites develop fingered branching structures with
high surface-to-volume ratio. Dendrites form through the
mechanism of morphological instability of smooth crys-
tals: fluctuations on th e front of a growing globular crys-
tal increase and turn into small, but visible bumps of dif-
ferent shapes, sizes, and velocities of growth (Figure
3(a)). Growing bumps communicate with each other
through thermal and diffusional fields and eventually
select a particular spacing through the mechanism of
competitive growth. Then the bumps turn into needles
(primary stems) with selected sh ape and speed of growth
(Figure 3(b)); later on the primary stems are overgrown
by sidebranches (Figure 3(c)). The sidebranches select
their spacing using the same mechanism of competitive
growth: some branches of a dendrite go extinct (passive
branches) and some survive down to the latest stages
(active branches) (Figures 1 and 3(d)) [53-55]. Dendritic
morphology includes rapidly moving convex tips of the
needles and sidebranches and non-changing concave
regions, called necks (Figures 1 and 3). The former are
surrounded by the supersaturated melt; the latter, due to
the negative curvature, are surrounded by unsaturated
melt which does not suppor t further gr owth of the crystal
(Figure 4). Specific details of the dendritic structure and
the rate of its growth depend on the driving ‘force’ that is,
the free energy change after crystallization (Figure 2).
The latter is proportional to the supercooling of the melt
or, if solute additives are present in the melt, supersatu-
ration of the solution before crystallization.
Dendritic growth is a highly cooperative mode of
crystal growth controlled by the long-ranged diffusive
field, thermal and/or species. It produces complex struc-
tures with the measure of complexity intermediate be-
tween that of a simple crystal and a DNA-like polymer.
On the lowest level one has to specify the symmetry of
the crystalline lattice and composition of the substance.
Figure 1. Dendritic structure of crystallization of pivalic
acid (from LaCombe et al.); reproduced with permission.
Figure 2. Free-energy versus temperature diagram of crys-
Copyright © 2011 SciRes. JMP
(a) (b)
(c) (d)
Figure 3. Time sequence of a growing crystal of ammonium chloride (a) init ia l fluctuat ions of the gl obular crystal; ( b) formati on
of the primary stems; (c) formation of the side-branches; (d) competition between the side branches (A. Dougherty, ou ghera/research/ crystal/index.html). The relative scale of the frames may be restored by compar-
ing the central parts of (a), (b), (c) and the tip radii of (b), (c), (d).
Figure 4. Numerical simulation of the dendritic growth in a binary alloy during directional solidification. Red, yellow, green,
and lime colors represent diffusion field between growing crystals with the red corresponding to the highest concentration
(lowest saturation) and lime—to the lowest concentration. (N. Provatas, J. Dantzig and N. Goldenfeld; reproduced with per-
Copyright © 2011 SciRes. JMP
On the second level the structure is characterized by the
periodicity of the side branches. The third level of com-
plexity specifies positions of the active and passive
branches in the system. The fourth level of dendritic
complexity describes properties of the envelope of the
dendritic structure—outline of the active branches.
Crystallization in supersaturated melts and solutions
occurs naturally and does not need any enzymes other
than inoculants of crystals (primary nucleation). If the
inoculants are external particles or surfaces, the process
is called heterogeneous nucleation [51, p. 93]. Dendrites
are prone to fragmentation (Figure 5) that is, breaking
off of small branches, which may be carried away from
the parent structure by fluid flows into regions of greater
supersaturation where they inoculate the solution (sec-
ondary nucleation) and start off another structure [51, p.
234]. Formation of dendrites in materials usually entails
formation of ‘grains’ that is, individual crystallites
formed by dendrites with different orientations obtained
at nucleation (Figure 6). When the grains meet each
other they form transition zones that is, grain boundaries,
and the whole material obtains grain structure [56]. Grain
boundaries are known to absorb trace components (atoms
and molecules of different sizes), which, notwithstanding
minute concentrations, significantly change properties of
the entire material, e.g. turn it from ductile to brittle [57 ].
4. Justification
Firstly, all life functions are defined in terms that apply
to living organisms only. To compare them to inorganic
counterparts, the definitions must be, so to say, stripped
off their ‘life statuses’ and considered just as natural pro-
cesses. Otherwise we create an artificial divide between
the organic and inorganic worlds, which may not allow
us to reveal important relations between the two. Sec-
ondly, the life functions, as exemplified by the extant
forms of life, are very sophisticated while the functions
of a dendritic crystal that are discussed below are rudi-
mentary. This, however, does not disqualify the latter
from the status of predecessors of the former.
Growth of an organism is defined as irreversible in-
crease in size and/or weight through synthesis of new
material. For dendrites growth is a natural process that
takes place under the appropriate conditions. Dendritic
structures grow by way of rejecting latent energy and/or
excess matter, a process which is greatly facilitated by
fingered morphologies. Metabolism is a set of chemical
reactions and transformations that require exchange of
matter and energy between the growing system and the
ambient environment, which serve the purpose of main-
tenance and propagation of the living system [58]. Den-
dritic metabolism is represented by rearrangement of the
molecular species of the melt or solution, which makes
maintenance and propagation of the crystal possible.
Figure 5. Fragmentation of dendritic crystals and their
subsequent motion due to fluid flow.
Figure 6. Granular structure of material after dendritic
crystallization. Notice formation of grain boundaries be-
tween dendrites growing with different orientation.
Copyright © 2011 SciRes. JMP
Similar to the life metabolism, the dendritic one is ac-
companied by the release of latent heat and/or mass ex-
cess and their subsequent removal from the growing
crystal. Unlike the life metabolism, the dendritic catabo-
lism (breaking down of organic matter and harvesting
energy) and anabolism (using energy to build compo-
nents) are not separated in space and time. Notice that
any process of crystal growth contains main traits of me-
tabolism: steady flow of mass/energy to drive the ma-
chinery and a mechanism to use the free energy excess
that comes with the flow for build-up of the new com-
ponents. However, compared with the growth of a glo-
bular crystal, the dendritic metabolism has an addition al,
essential component. This is creation of the large amount
of surface area, which is vital for dendrites because
mass/energy exchange with ambience goes through the
surface (Figures 1, 3 and 4). Although free-energy re-
duction is the driving force of the growth (see Figure 2),
additional surface area increases the free energy of the
dendritic crystal compared to that of the globular one of
the same volume. In other words, dendritic metabolism
does not proceed completely ‘downhill’ (free energy
decrease), it has an ‘uphill’ component (free energy ex-
cess) associated with the surface area creation. High
density of interfaces in dendritic structures allows them
to speed-up metabolism that is, remove heat and matter
faster. The difference from a biological cell where this
function is played by enzymes is that biological metabo-
lism causes chemical changes, while dendritic metabo-
lism causes phase changes.
Branching of dendrites may be considered as relic di-
vision. The most prominent property of the branching
mechanism is its periodicity with the new branches being
almost exact copies of the old ones. However, the new
branches are more than just repetitions of the old ones
because they carry information about the complexity of
the whole structure; for instance, some of the branches
are ‘doomed’ to stop growing very early, while others
will grow up to large sizes (Figures 1 and 3(d)). The
mechanism of periodic branching is similar to biological
replication, which may be defin ed as “the abilit y to make
copies of an information carrier” [59]. The difference is
that the dendritic branching is an example of three-di-
mensional replication rather than one-dimensional repli-
cation of DNA. Contrary to amphiphilic vesicles that
need external forcing for division [9,12], dendrites divide
and replicate naturally because they ‘do’ this far from
Biological organisms contain genetic information
which regulates their replication. Orgel [40] defined ge-
netic in- formation as “the minimum number of instruc-
tions needed to specify the structure”. Genetic informa-
tion of a dendrite, according to Orgel’s definition, is en-
crypted in its structure: it is contain ed in the special posi-
tions and sizes of the branches, same way as barcodes
contain information about the product. Dendrites grow as
self-similar, self-replicating structures with strict hier-
archal order of branches, which is reminiscent of the
order of generations in biological systems. Hierarchal
structures of dendrites allow for the replication and
propagation of genetic information from generation to
Mutations in living organisms are defined as sponta-
neous changes of genetic information (DNA sequence).
If the changes are ‘found to be useful’, they become
permanently reflected in the reproductive process—
natural selection. In abiotic systems, including dendrites,
mutations correspond to thermal fluctuations and are
similar to the genetic drifts. Dendritic fluctuations occur
naturally because of the statistical nature of the systems;
they appear in the form of small bumps, which compete
for the fresh, unprocessed material in front of them
(Figure 3(a)). A growing crystal produces more bumps
than can survive to significant sizes. The bumps vary in
the form and position; only those of them turn into nee-
dles which will make the nascent structure more efficient
(Figure 3(b)). Later on, needles themselves will be cov-
ered by small bumps, future branches (Figure 3(c)),
many of which will perish (passive branches) and on ly a
few will survive (active branches) (Figures 1 and 3(d)).
The survival of the dendritic branches is based on their
geometrical positioning and timing of their appearance,
which is the ‘dendritic way’ to pass genetic information
to the future generations and, hence, make the mutation
permanent. Although the selection principle for dendritic
growth is still an activ e subject of research in the ph ysics
of pattern formation [49], it is absolutely clear that this
principle is based on the stability of the growing struc-
ture. Thus dendritic structur es demonstrate natural selec-
tion—differential reproduction—driven by stability and
growth competition. This concludes the justification that
dendritic structures possess all the essential characteristic
functions of the living systems: growth, metabolism,
division, replication, mutation and evolution in the form
of natural selection.
Besides the basic functions of life, one can also see
that dendritic structures possess built-in homeostasis.
Indeed, if the ambient conditions change, e.g. tempera-
ture, pressure, or chemical potential, dendritic structures
respond in many different ways in order to maintain the
operating conditions. For example, if the temperature
drops dendrites start growing faster, releasing more la-
tent heat; this bring s the surround ing temperature b ack to
almost where it was before. Dendritic homeostasis does
not come as a big surprise because, as known, homeosta-
sis of biological organisms is an extension of the Le-
Chatelier’s principle of the ab iotic world. Ho wever, th ere
is another type of dendritic response to changing condi-
Copyright © 2011 SciRes. JMP
tions: dendrites make adjustments in the spacing s of their
primary and secondary branches [60,61]. At large super-
coolings dendritic needles lose their branches and the
crystal grows with spherulitic morphology. If the super-
cooling is great enough, the crystal may lose the needles
all together and grow as a smooth entity [55,62]. One
may consider these modifications as an example of den-
dritic adaptation. Thus, I have shown above that den-
dritic crystals possess all the basic biological functions.
In addition, one can notice that the organic world has
‘intricate relations’ with the dendritic morphologies. To
begin with, many pure organic materials and their aque-
ous solutions und ergo dendritic crystallizat ion wh en they
are cooled below their liquidus temperatures. Typical
examples are ammonium chloride [63], pivalic acid [64],
cyclohexanol [62], succinonitrile [54], cholesterol [65],
and protein streptavidin [66-68]. Under ‘lagoon-like’
conditions aqueous solutions of potassium cyanide and
ammonium hydroxide yield heterogeneous cyanide
polymer particles [69]. When these particles were dis-
solved in dimethyl sulfoxide and allowed to dry on a
microscope slide, they showed branched tubular mor-
phologies reminiscent of snowflakes. Nucleotides and
amino acids are known to crystallize with dendritic and
spherulitic morphologies. Ramachandran and Natarajan
[70] showed that L-tyrosine crystallizes in silica gel
having spherulitic morphology with long needles. This is
also true regarding the crystallization experiment of
Shinitzky et al. [27] (D. Deamer, personal communica-
tion). Dendritic pattern of liquid-crystal growth in or-
ganic materials is a common place [71]. Spontaneous
ordering of high concentrations of short strands of nu-
cleic acids into a liquid crystalline phase displays den-
dritic structures [72]. Importantly that this process pro-
motes selection and segregation of complementary se-
quences and ligation of neighboring strands by physical
Furthermore, organic additives change crystallization
pattern of many inorganic substances. Lopezcortes et al.
[73] studied influence of halobacteria in the crystal for-
mation of halite. Their analysis suggests that the pro-
teinaceous constituents of extremely halophilic archae-
bacterial surface layers may determine the crystal form
of halite and even “yielded dendritic crystals”. Shibata et al.
[74] studied effect of human bloo d additions on dend ritic
growth of cupric chloride crystals in aqueous solutions.
Their evidence suggests that components of blood in-
cluding amino acid, peptide and/or protein or some
composition of them were chemisorbed on the dendrite
surfaces. Eiden-Abmann et al. [75] studied the influence
of amino acids on the formation and morphology of hy-
droxyapatite (calcium phosphate) in gelatin. They found
that additions of amino acids (Asp, Glu, Ser, etc.) to the
gelatin results in formation of spherulites consisting of
many thin needles. Then, one can imagine how these
materials grew from the prebiotic soup (heterogeneous
mixture of organic compounds) once the temperature on
early Earth was dropping below their liquidus tempera-
Moreover, the dendritic morphology confers opera-
tional advantage to extant forms of life. Many plants
have forms reminiscent of dendritic crystals [76] (al-
though in crystals energy is received from outside while
in plants—from inside [77]) and great similarities exist
between the cellular morphology of plant tissue and
structure of binary alloys undergone directional crystal-
lization [78]. Animal bones have dendritic structure to
allow for fluid flow through them [79]. Bacterial colo-
nies, growing under conditions of starvation, form den-
dritic morphologies [80]. Also bacteria can trigger min-
eral formation under saturation conditions, but the rea-
sons why bacteria favor or promote mineral nucleation
are still unclear [81]. The nerve cells, neurons, have
branching structures (also called dendrites due to their
tree-like morphologies). Observations of neurons of dif-
ferent species suggest that neural branched geometry is
certainly related, in part, to the expression of genetic
factors, which are present during phylogenesis [82].
Even the process of transcription of DNA into RNA has
dendritic morphology with DNA representing a primary
stem and RNAs—sidebranches [83]. Curiously, the phy-
logenetic tree itself is morphologically very similar to
crystalline dendrites, e.g. it has passive branches and
active ones [84].
To summarize, on the one hand, dendritic crystals
were present on the early Earth; on the other hand, den-
dritic morphologies are broadly utilized by extant forms
of life. Hence, we may envision that the two are evolu-
tionarily connected through a kind of ‘branching gene’.
Starting off with a dendritic-arms gene of the protobiont,
which as we saw above can hold replicable information
favoring its own propagation, it evolved into something
like a clay gene [85] and a DNA gene at a later time.
The hypothesis of the dendritic nature of protobionts
allows us to establish an alogy between the existing com-
ponents, functions, and other processes of biological or-
ganisms and their primordial counterparts. For example,
crystallization is analogous to polymerization; nuclea-
tion—to heterogeneous catalysis; fragmentation of den-
dritic structures plus secondary nucleation of new struc-
tures is analogous to migration and ‘gene flow’ in bio-
logical systems. Grain structure of the material after cry-
stallization is an analogue of cellular organization with
the grain boundaries playing the role of cell membranes.
The species segregated at the grain boundary are analo-
gous to the membrane proteins, which are responsible for
charge transfer through the membrane. According to my
Copyright © 2011 SciRes. JMP
hypothesis, the supersaturated solution is the forerunner
of the food for modern organisms, while the unsaturated
one—of the waste; crystal grains are prototypes of cells
(preprocaryotes), and dendritic bran ches—of generations.
Many authors noted profound similarity between the
processes of crystal growth and enzymatic chemical re-
actions [8,85]; hence, mineral surfaces and inoculants are
primordial enzymes and active sites. Diffusion of charge,
heat, and solutes served as the transport system through
premembranes and was part of the fossil metabolism. As
known, individual cells have ability to sense chemical
gradient and cell’s development appears to be regulated
by diffusible molecules—the process of chemo taxis.
Hence, chemo- and thermo-taxes of microorganisms are
rooted in the chemo- and th ermo-taxes of dendrites (pro-
tobionts). A very high surface-to-volume ratio of den-
dritic structures was certainly favorable for catalysis of
other biological reactions and transformations on their
surfaces-prebiotic autocatalysis. Morphology of den-
drites is their phenotype while complexity —th e genotype.
Genotype and phenotype of the primordial organism
were not separated (‘naked gene’ of sorts, [46]), which is
analogous to RNA world where one molecule (RNA)
combined both types. These relations are reflected in the
Table 1 below.
5. Scenarios of the Origin of Biological
If one accepts the geological data that support the fact
that around the time of the origin of life early Earth was
very near the freezing point of water [86-89], then the
dendritic protobiont hypothesis may allow one to con-
jecture a scenario of thermo-chemical precipitation of the
biologically important material. Monomeric components
of the genetic apparatus precipitated in shallow water
pools of dilute multi-component aqueous solutions of
diverse organic molecules with the surfaces of rocks or
Table 1. Analogy between the extant components, functions, and other proc esses in bi ological organisms and their primordial
Existing (biological) Primordial (dendritic protobiont)
Organism Dendrite
Properties (phenotype) Morphology of the structure
Genetic information (genotype) Complexity of the structure
Generations Dendritic branches
Food Supersaturated solution
Waste Unsaturated solution
Active sites and enzymes Mineral surfaces and inoculants
Cell Crystal grain
Cell membrane Grain boundary
Membrane protein Species segregated at the grain boundary
Main Functions
Growth Growth
Metabolism Rearrangement of the molecular species plus diffusion of excess heat and/or species
Division Branching
Replication Periodicity of branching
Mutation and genetic drift Thermal fluctuations
Natural selection Selection principle?
Other Functions and Processes
Polymerization Crystallization
Heterogeneous catalysis Heterogeneous nucleation
Migration and gene flow Fragmentation plus secondary nucleation
Homeostasis LeChatelier’s mechanism
Adaptation Geometrical position and timing of branches
Copyright © 2011 SciRes. JMP
clays serving as catalysts of nucleation. The newly pre-
cipitated crystals grew by dendritic mechanism. When
dendrites grow from aqueous solutions the supersatura-
tion of the solution can be achieved through the proc-
esses of cooling and/or drying, both of which took place
in pools of water on early Earth. Different substances
have ability to precipitate from aqueous solutions using
different mechanisms of growth. However, dendritic me-
chanism conferred an evolutionary advantage because,
arguably, it is the fastest mechanism of growth, and the
competition between a few substances that precipitated
from aqueous solution by different mechanisms was won
by dendrites—the quick had better chance to come alive
on early Earth. “Selection pressure favors any chemical
system that can process matter more rapidly and make
more of its kind.” [58] Due to highly cooperative nature
of crystallization, dendritic structures created high con-
centrations of biomonomers at one place—the concentra-
tion gap problem. The genetic materials of increased
sophistication appeared through the successive and over-
lapping stages of material coevolution where the den-
dritic protobionts were on the lower steps of the case and
the organic biomaterials on the upper ones, “a genetic
staircase”-type scenario [18]. Branching morphologies,
once started as a physico-chemical process, ‘entered’ the
genome on the later stages of evolution.
This scenario may apply to amino acids whose crystal-
lization is known to purify the material from water [27]
and make the reaction of polymerization more probable.
High cooperativity o f crystallization could have been the
reason for the appearance of biochirality because den-
dritic crystallization is also known to enhance the SCSB
mechanism through fragmentation [11,22,23]. Periodic
temperature variations, e.g. due to circadian cycles, pro-
vided the source of free energy and caused periodic
freezing and thawing of dendritic structures with the re-
action of polymerization taking place in the molten state.
New cycles of crystallization led to formation of more
and more organized matter with clearly living functions.
In a way, these cycles were the first example of evolution
by way of extinction and speciation [90,91]. A set of
experiments may be suggested to test this scenario. For
example, one may subject a dilute solution of amino ac-
ids to periodic temperature variations around the freezing
point and watch for the formation and growth of peptide
chains in the solution.
One may envision other scenarios that also allow
transferring dendritic functions onto the organic world;
for instance, formation and growth of inorganic crystals,
e.g. calcite (CaCO3) [92], in the prebiotic conditions and
subsequent adsorption of organic substances on their
surfaces [25,26]. This mechanism, however, has been
considered in the literature and will not be elaborated
here any further. Notice that all scenarios indicate that
biochirality appeared together with the first signs of life
and cellular organization.
6. Discussion
Based on the fact that growth of dendritic crystals of
inorganic or simple organic molecules possesses all basic
functions of life and may contain ‘genetic’ information
stored in their branches, I presented a hypothesis of the
dendritic nature of a protobiont. According to this hy-
pothesis the protobionts formed through a physico-che-
mical process known as dendritic crystallization. The
branching dendritic crystalline structures helped build
living systems by lending them functions so that organic
chemical evolution is just one natural consequence of the
evolution of matter in the universe. A self-replicating
biological system with adaptation emerged from simple
molecules using a completely abiotic mechanism of
nonequilibrium phase transitions. Dendritic structures
assisted the emergence of the genetic apparatus, which
otherwise would have been thermally improbable. This
mechanism could act simultaneously or intermittently at
different places on the early Earth and created similar
structures everywhere. Hence, to explain the similarities
in the living systems there is no need to invoke the con-
cept of LUCA because, according to the hypothesis, they
arise as a result of thermodynamic necessity. The den-
dritic protobion t hypothesis supports the assumption of a
‘second genesis of life’ [30,93] and helps explain why
“life established itself on Earth fairly quickly once con-
ditions permitted” [33]. Th e full and complete biological
functionality was already lurking ‘deeply in the inorganic
world’, waiting to be revealed and utilized. Althoug h the
dendritic crystals were the living organism in the pri-
mordial world, they should not be considered contempo-
rary living systems because they are not made of the
right material, macromolecules. One should not forget
also that the primordial conditions were completely dif-
ferent from the present ones.
Although there are other abiotic systems that possess
some of the biological functions, significance of the
dendritic crystal growth mechanism is in that it possesses
all of the basic life functionality. Obviou sly, the dendritic
scenario does not necessarily need carbon-based solutes
in water-based solutions; it can work with e.g. sili-
con-based solutes and/or hydrogen sulfide-based solvents.
This may have an important implication for extraterres-
trial origin-of-life scenarios.
7. Acknowledgements
The author is indebted to R. Shapiro of NYU and A.G.
Cairns-Smith of UG for their sugg estions and would like
to thank D. Deamer of UCSC, M. Simakov of RAS, and
Copyright © 2011 SciRes. JMP
S. Maurer of SDU for helpful discussions. Support for
this research was prov ided by NSF Gr ant DMR-0244398
from the Material Theory program and FSU’s Research
Center for Health Disparities granted by NIH.
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