by Charles Baum
home as long as the colony consists of fewer than about 80,000 indi-
viduals. Exceed that number of army ants, however, and the colony
exhibits new emergent behavior; like a bursting dam, the ants pour out
in a massive “swarm raid” to attack adjacent colonies. At higher popu-
lations, half of the ants may spontaneously leave to form a new colony.
Studies of termite colonies also reveal that the construction of pillar-
type mounds requires a critical density of individuals.
At a much greater scale, spiral galaxies require a minimum num-
ber of about 100 million stars to trigger development of the familiar
spiral arm structure. According to theoretical models of astrophysi-
cists, the majestic arms form as a result of gravitational instabilities
caused in part by a large central mass of stars.
Human consciousness and self-awareness also emerge from the
interactions of trillions of neurons. Sadly, as those of us who watch
friends and relatives afflicted with Alzheimer’s disease must observe,
when a critical number of cells and their connections are destroyed,
self-awareness fades away.
These findings suggest that the emergence of life might have de-
pended on achieving some minimal concentration of biomolecules,
the essential agents of cellular life. Too few molecules, no matter how
friendly the environment, and life could not arise. That’s a useful idea
to bear in mind when designing origin-of-life experiments.
Factor 2: The Interconnectivity of Agents
Sand grains influence each other by direct contact, the simplest local
way to interact. A rounded grain at the surface of a sandpile typically
touches about a half-dozen adjacent grains. The balance between these
20
GENESIS
stabilizing contacts and gravity on the one hand, and the restless, dis-
ruptive flow of water on the other, leads to a controlled shuffling of
grains and ultimately to the rippled patterning of sand. By contrast,
ants in an ant colony interact over much greater distances, by marking
the ground with a variety of pheromones, which are chemical signals
that point other ants to food, alert them to danger, and provide other
vital information. In this way, any given ant has the potential to inter-
act with thousands of colony mates in varied ways. These differences
in interconnectedness provide part of the reason why ant colonies are
more complex than water-shaped sandpiles.
The conscious brain, the most complex system we know, is also
the most complexly interconnected. Each of the trillions of neurons in
your brain interacts with hundreds of other nearby cells through a
branching network of dendrites. Electrical signals between any two
neurons, furthermore, may be stronger or weaker, like the current con-
trolled by the dimmer switch on your lamp. Interconnections of the
brain are vastly more intricate than those of sand or ants.
These observations of emergent systems suggest that life’s origin
must have relied on a wide repertoire of chemical interactions. Experi-
ments that optimize the number and type of molecular contacts might
thus be more likely to display emergent behaviors of interest.
Factor 3: Energy Flow Through the System
Regardless of how many sand grains or ants or neurons are present, no
pattern can emerge without a flow of energy through the system. Sand
grains will not start hopping without a certain minimum water-wave
speed (typically about 1/ to 1 meter per second along the shores of the
2
Chesapeake Bay). More energetic waves with greater speed and ampli-
tude move grains more easily and generate sand patterns more quickly,
though these patterns do not appear to differ fundamentally in their
shapes.
But every complex patterned system has a limit to the magnitude
of energy flow it can tolerate. During energetic storms, crashing waves
obliterate sand ripples and other local sedimentary features. Black and
tan sand grains become jumbled and all signs of emergent patterning
disappear.
The human brain exhibits strikingly similar behavior in terms of
energy flow. During normal waking hours, the brain maintains a mod-
THE MISSING LAW
21
erate level of electrical impulses—the normal healthy flow of energy
through the neural system. Deepest sleep corresponds to a sharp drop
in electrical activity as we slip from consciousness, whereas the exces-
sive electrical intensity of an epileptic seizure thwarts conscious action
by scrambling the usual patterned electrical flow.
The emergence of complex patterns evidently requires energy flow
within rather restrictive limits: Too little flow and nothing happens;
too much flow and the system is randomized—entropy triumphs. This
conclusion is important for the experimental study of life’s chemical
origins. A reliable source of energy is essential, to be sure, but light-
ning, ultraviolet radiation, and other intense forms of ionizing energy
can blast molecules apart and may be too extreme to jump-start life.
We must look for gentler chemical energy sources, like the steady, reli-
able chemical potential energy stored in a flashlight battery, to sustain
the metabolism of primitive life.
Factor 4: Cycling of Energy Flow
Many natural systems are subject to cycles of energy: day and night,
summer and winter, high tide and low tide. Such cycles may play a
fundamental role in the evolution of emergent systems, though it’s of-
ten difficult to document the effects of these subtle cycles in nature.
Laboratory wave tanks, though considerably less scenic than the
Chesapeake Bay in January, facilitate the study of sand-ripple forma-
tion under controlled conditions. Recent research on natural patterned
systems reveals that cycling of energy flow through a system is a fasci-
nating and previously unrecognized fourth factor in generating com-
plex sand patterns. In 2001, physicist Jonas Lundbek Hansen at the
Niels Bohr Institute and his Danish colleagues announced this surpris-
ing wrinkle in the mechanics of ripple formation. Most previous ex-
periments had involved fixed wave amplitudes (that is, wave height)
and frequencies (how many waves pass a given point in a second). Such
studies typically generate perfectly spaced, straight ripples. Instead,
Hansen and his colleagues wondered what might happen if they cycled
these variables. Over periods of several minutes, they increased and
then decreased the amplitude or the frequency of their water waves.
The results were breathtaking. Rather than simple parallel sand ripples,
they produced elegant intertwined and branching sand structures.
These new patterns appear remarkably similar to sand features that
22
GENESIS
commonly arise along the Chesapeake Bay when the water is only a
few inches deep—conditions that apparently favor periodic fluctua-
tions in wave amplitude.
Alert to the potential power of energy cycling, PhD student Mark
Kessler and Professor Brad Werner of the Un
iversity of California, San
Diego, recently analyzed amazing stone circles and other so-called “pat-
terned grounds” in Alaskan Arctic terrain that is subject to cyclical
freezing and thawing. With each thaw, rounded boulders shift slightly,
interacting with one another over many years to produce remarkable
fields covered by natural circles of stone. [Plate 2]
The role of cycling in the emergence of patterns represents a fron-
tier area of study that is keenly watched by some origin-of-life investi-
gators. After all, the primitive Earth was subject to many cycles—
day/night, high tide/low tide, wet/dry, and more. Perhaps such cycles,
which can be duplicated in a controlled experimental environment,
contributed to the emergence of life itself.
FORMULATING EMERGENCE
So what might a mathematical law of emergence look like? My guess is
that the expression will take the form of a mathematical inequality,
something like this:
C ≤ f[ n, i,∇ E( t)]
That’s a short-hand way of saying that the emergent complexity of
a system, denoted by the letter C (for “complexity”), is a number less
than or equal to some value that is a mathematical function ( f) of the
concentration of interacting particles ( n), the degree of those particles’
interconnectivity ( i), the time-varying energy flow through the system
[∇ E( t)], and perhaps other variables as well.
At least two daunting impediments thwart the completion of this
potentially simple formulation. First, as previously noted, we lack a
precise definition of complexity. It’s impossible to quantify something
when you don’t really know what that something is. And second, we
are woefully ignorant of the exact mathematical relationships between
complexity and the three possible key factors: the concentration of in-
teracting agents, the interconnectivity of those agents, and the cyclical
THE MISSING LAW
23
energy flow. Simple systems yield tantalizing clues, but we are still a
long way from any definitive formula.
This quest to characterize emergent phenomena, though initially
couched in mathematical abstraction, is not ultimately an abstract ex-
ercise. Emergent systems frame every aspect of our experience. Our
environment, our bodies, our minds, the patterns of our lives and our
culture—all display emergent complexity. A comprehensive theory of
emergence will foster applications to myriad problems in everyday
technology: long-range weather prediction, computer network design,
traffic control, the stabilization of ecosystems, the control of epidem-
ics, perhaps even the prevention of war. Armed with such a law, we will
acquire a deeper understanding of any system of many interacting
agents—indeed, even of the origin of life itself.
2
What Is Life?
I know it when I see it.
Justice Potter Stewart, 1964
Arecent origin-of-life text features an appendix with scientific defi-
nitions of life written by 48 different authorities. The entry con-
tributed by the distinguished evolutionary biologist John Maynard
Smith describes life as “any population of entities which has the prop-
erties of multiplication, heredity and variation.” Alternatively, infor-
mation theorist Stuart Kauffman claims that “life is an expected,
collectively self-organized property of catalytic polymers.” Other
equally renowned experts propose that “Life is the ability to communi-
cate,” “Life is a flow of energy, matter and information,” “Life is a self-
sustained chemical system capable of undergoing Darwinian
evolution.” The definitions go on and on. Remarkably, no two defini-
tions are the same.
This lack of agreement represents an obvious problem for those
who search for signs of living organisms on other worlds, as well as for
origin-of-life researchers. It is difficult to be sure that you’ve discov-
ered life—or deduced the process of life’s origin, for that matter—when
you can’t define what it is. In spite of generations of work by hundreds
of thousands of biologists, in spite of countless studies of living organ-
isms at every scale from molecules to continents, we still have no widely
accepted definition.
This frustrating lack is not particularly surprising. For one thing,
the question “What is life?” is asked in different contexts by different
professions. Theologians hotly debate it in relation to the beginning of
human life. Does life start at the moment of conception, when the fetal
25
26
GENESIS
brain first responds, or when the unborn heart first beats? In some
theologies, life commences not with a physical process, but at the un-
knowable supposed instant of ensoulment. At the other end of the hu-
man journey, doctors and lawyers require a definition of life in order
to deal ethically with patients who are brain dead or otherwise termi-
nally unresponsive.
In contrast to these ethically complex and emotionally charged is-
sues are the more abstract scientific efforts to define life. Biologists rely
on straightforward genetic analysis—tests for DNA or diagnostic pro-
teins—to identify the presence of life-forms on Earth today. But a more
general definition that distinguishes all imaginable living objects from
the myriad nonliving ones remains elusive. We know relatively little
about the diversity of cellular life on Earth, not to mention the vast
range of plausible noncellular life-forms that might await discovery
elsewhere in the universe. Endorsing a sweeping definition of life based
on such scanty knowledge is akin to defining “music” after listening to
a single recording of Bach’s solo cello suites over and over again. The
suites are a sublime example of music, but hardly sufficient to charac-
terize the entire genre.
“TOP-DOWN” VERSUS “BOTTOM-UP”
Scientists crave an unambiguous definition of life, and they adopt two
complementary approaches in their efforts to distinguish that which is
alive from that which is not. Many scientists adopt the “top-down”
approach. They scrutinize all manner of unambiguous living and fossil
organisms to identify the most primitive entities that are, or were, alive.
For origin-of-life researchers, primitive microbes and ancient micro-
fossils have the potential to provide relevant clues about life’s early
chemistry. This strategy is limited, however, because all known life-
forms, whether living or fossil, are based on biochemically sophisti-
cated cells containing DNA and proteins. Any definition of life based
on top-down research is correspondingly limited.
By contrast, a small army of investigators pursues the so-called
“bottom-up” approach. They devise laboratory experiments to mimic
the emergent chemistry of ancient Earth environments. Eventually, the
bottom-up goal is to create a living chemical system in the laboratory
from scratch—an effort that might clarify the transition from nonlife
to life. Such r
esearch leads to an amusing range of passionate opinions
WHAT IS LIFE?
27
regarding what is alive, because each scientist tends to define life in
terms of his or her own chosen specialty. One group will focus on the
origin of cell membranes; to them, life began when the first encapsu-
lating membrane appeared. Another team studies the emergence of
metabolic cycles, so naturally for them the origin of life coincided with
the origin of metabolism. Still other groups investigate primordial
RNA (DNA’s presumed precursor genetic material), viruses, or even
artificial intelligence, and each group hawks its own definition of life’s
first appearance.
Into this mix, philosophers and theologians inject a more abstract
view and speculate on the full range of phenomena that might be said
to be alive—robotic life, computer life, even a self-aware Internet. Such
debates can at times sound like a science fiction convention, but defin-
ing life is no idle exercise. The scientific community, with the full sup-
port of NASA and other governmental agencies, holds regular meetings
to debate the question. After all, one of NASA’s prime missions is to
look for life on other worlds, so a clear definition is essential for plan-
ning future missions.
It’s amazing how the “What is life?” question sparks arguments
and fosters hard-line positions. Scientists excel at many things, but
compromise is not always one of them. Nevertheless, Gerald Joyce of
The Scripps Research Institute, serving on a NASA Exobiology panel,
proposed a widely cited “working definition” for life in the context of
space exploration. “Life is a self-sustained chemical system capable of
undergoing Darwinian evolution,” he suggested.
According to this opinion, life combines three distinctive charac-
teristics. First, any form of life must be a chemical system. Computer
programs, robots activated with microchips, or other electronic enti-
ties are not alive according to this definition. Life also grows and sus-
tains itself by gathering energy and atoms from its surroundings—the
essence of metabolism. Finally, living entities must display variation.
Natural selection of the more fit individuals will inevitably lead to evo-
lution and the emergence of more complex entities. This NASA-