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Almost an Angel

How do the complexities of the living world arise from dumb matter? A speck of angelic assistance may be all that's needed.

Michael Brooks

My Angels and Demons at War - RUSHARE you ever, when absent-mindedly cleaning the house, troubled by those deep philosophical questions? You know the sort of thing. How did we get here? What is the meaning of life? Why does a collection of carbon, hydrogen and oxygen atoms like me feel the need to ask such difficult questions?
The answers probably won't come to you while you're still cleaning, so stop dusting and pay attention to Sorin Solomon, a physicist at the Hebrew University of Jerusalem. Solomon has discovered that adaptive, almost intelligent behaviour can emerge from the interaction of just two very stupid kinds of entity. We'll call them angels and mortals. From their simple dance comes an explanation for our very existence.
These ideas are embodied in a game that Solomon developed last year. In a paper submitted to the National Academy of Sciences, he shows that life gains the upper hand in what ought to be disastrous circumstances. It has other happy consequences, too. It shows that financial markets will survive even in the hands of dunces. In the future it could even provide you with an army of robot cleaners. So put your feet up, pour yourself a glass of some-thing refreshing, and drink a toast to Solomon's angels.
The complexity of any system, such as life on Earth, must somehow arise from the interaction of its simplest parts. If you can find and map those simple interactions, whole areas of seemingly impenetrable complex phenomena should be laid bare. Such "microscopic representations" can be used to break down the Universe into galaxies, and a nucleus into protons and neutrons. See how the component parts work, then put them back together again, and you should have an explanation of the most complex phenomena.
Solomon and his team work from the bottom up, with what they consider to be the most basic of ingredients. First they scatter a race of "mortals" evenly over a square grid. Life for these beings is bleak, as every hour a fraction of the population dies. But there is also a ray of hope, in the form of eternal agents, or "angels", scattered over the board. The mortals and angels hop around randomly like soot particles in Brownian motion. There is only one rule: when mortal and angel meet, the mortal multiplies. There, in the presence of immortality, a life begins.
What fate awaits this world? Well, that depends on how you look at it. If you stand far from the playing board, you see only a smeared-out cast and not the individual players. Given the average population densities of angels and mortals, you can work out an equation that predicts the average death rate and birth rate. If the mortals die out faster than they are born, the race becomes extinct. This way of looking at the world is called the "continuum approach".
But with Solomon's microscopic representation, the outcome is starkly different. Although the population slumps at first, it can recover. "It constitutes the difference between life and death," says Solomon. Whereas the continuum approach predicts extinction, the direct simulation uncovers the emergence of a thriving, developing system. "The continuum is utterly misleading," says Solomon.

CAN RANDOM ENVIRONMENTAL FLUCTUATIONS INCREASE AIR POLLUTION LEVELS? A new paper suggests this possibility. Motivated by the problem of ozone production in urban areas, an Arizona State team (Zonghua Liu, 480-965-2311, simulated a chemical reaction between tens of thousands of hydrocarbons and nitrogen oxides in a two- dimensional airflow. In actuality, the production of ozone requires dozens of distinct chemical species and a chain of sunlight- triggered chemical reactions. Yet in their single reaction between two species the researchers were able, for the first time, to consider how the reactants' size and mass affect their rate of chemical reaction in the complex 2D flow they examined. Moreover, the simulated 2D flow has important similarities to real-life airflows in the troposphere, the approximately 15 kilometers above ground where air pollution can occur. For example, the simulations explored a situation that can sometimes occur in real-life tropospheric flows: "Lagrangian chaos," in which the overall flow of air is regular (completely predictable) but the individual particles in the air move in a chaotic (unpredictable) fashion. In efforts to mimic the repeating cycle of day and night, the researchers incorporated a repeating cycle that influenced the reaction. Most strikingly, however, the chemical reaction rates were increased by up to two times when the researchers added the right amount of environmental "noise," random fluctuations, such as wind-speed variations, whose intensity depends on temperature. As it turned out, the addition of noise caused the behavior of particles to become more spatially and temporally regular. This in turn created favorable conditions for increasing the chemical reaction rate. This result suggests that perhaps environmental noise plays an important role distinct from other effects in generating air pollution. If borne out this would represent the latest natural example of stochastic resonance (Update 121), in which an ordinarily weaker process can be magnified by the right amount of random fluctuations ("noise") in the background. The researchers' next step is to study chemical reactions in more realistic flows. (Zonghua Liu; Ying-Cheng Lai; and Juan M. Lopez, Chaos, June 2002)

Why should that be? When Solomon looked closely at his game, he found that some groups of mortals, though completely ignorant of everything around them, appear to follow the angels around. Thanks to the new births in each angel's presence, there is an overall increase in the mortal population at these sites. The new mortals move randomly away from their birthplace, but if the angel's random hop is onto their turf, they multiply again. The result is islands of life that move around the playing area, following their angels. Islands can grow, join and split up again. Small islands are unstable, but can become more stable when they merge to form larger islands. Because of this apparently adaptive behaviour, the pockets of population survive and proliferate. Ever the underdog, life simply blows a raspberry at the big bad world.
But Solomon's mortals are totally unaware of their environment, and have no life goals. "We start with very stupid microscopic components. The islands are made up of individuals who don't have the slightest clue of where they are going," says Solomon. "The microscopic agents are nonadaptive, but the collective object has a behaviour which can be called adaptive." This is not a conclusion that can be drawn from other simulations, says Solomon. He points to "adaptive agents", generated by John Holland, a simulations expert at Michigan State University. According to Solomon, Holland's agents have complexity already built in. "They have strategies, efficiency criteria, and make choices," he says. "Since you are putting it in, you can't claim that you are studying the emergence of adaptability."
Holland takes the opposite view. He says he would hesitate to describe the behaviour of Solomon's system as being adaptive. He likens it more to a kind of self- regulation maintained by feedback. For instance, when the body's sensors register a high temperature, they trigger the sweating mechanism. "Of course there are no sharp lines here, so the distinctions are almost a matter of convenience."
Solomon and his colleagues insist their model is genuinely adaptive. "The islands are not just self-regulating, they are selfserving. They move in a way that prolongs their life," he says.
If adaptability really does emerge at this basic level, the implications are far-reaching. For instance, the angels could represent the necessities of life, such as edible animals for a population of carnivores. Most researchers into population dynamics would treat the animals as a resource that is spread evenly across the whole area. With just a few animals, the situation would look grim: there just wouldn't be enough meat in a given area to allow the carnivores to survive. But Solomon's microscopic view reveals that a few animals are bound to be in just the right place, allowing a few bands of carnivores to become established.
Jeff Kirkwood, a population dynamics researcher at Imperial College, London, says this close look is particularly valuable when predicting population growth in a diverse environment. "If you looked 'on average', the conditions are just hopeless and no one has any right to survive," he says. But if there are patches where it is possible to survive, some faster-growing species like pest plants and bacteria can hang in there for ages. "As soon as the conditions get good in one little area, up they come," says Kirkwood.

Cherubic chessgame - Le ROI et Mort-Vive Le ROI
Guardian angels: even though mortals move at random over the board, they survive by forming islands that follow the angels around.

The number of dimensions available on the playing board turns out to be crucial. If Solomon lets his angels and mortals move in three dimensions instead of two, the players tend to cross each other's paths too rarely for life to survive. But with just two dimensions, life always wins. Even with a high death rate, a single angel enables life to flourish on Solomon's two-dimensional board.
"This may explain the fact that most ecological systems are two-dimensional," says Solomon. Even creatures that can move in three dimensions, like birds, fish and microbes, tend to stick with one particular level, limiting themselves to largely two-dimensional movement because their particular angels-be they light, oxygen or food-tend to be found within a small vertical range.
According to John Beringer, an expert on microbial biology at the University of Bristol: "Microbes that need oxygen will be found close to the surface of soil, and microbes that are very fastidious about oxygen concentration will be found in bands at the appropriate oxygen concentration." Microbes concentrating on a two-dimensional resource may have been more successful than their cousins who tried exploiting a three-dimensional feast.
Set up the game in a slightly different way, says Solomon, and it can explain why there is no such thing as a duckbilled hippopotamus. Instead of a place in real space, like a stretch of savannah, the playing area could represent all possible ways in which genes can be arranged. Biologists call this sort of abstract space a fitness landscape.
Now think of Solomon's angels as the perfect genomes for the habitats and niches available, and the mortals as species wandering through the fitness landscape. Far away from the perfect genome,a species will probably fade out of existence. But around the angels, islands of similar species will develop.
"The space of species is very sparsely populated-there is nothing in the 'space' between giraffes and elephants, or between lizards and snails," says Solomon. The finite number of environments that exist on Earth significantly reduces the number of genomes that can survive.
And what about the chemicals that needed to co-exist in order to create life? The angels and mortals in Solomon's game have such simple properties that they could be single molecules. Their playing space could be something like the Earth's prebiotic oceans, where all that existed were a few relatively simple compounds. As these primordial chemicals floated through the waters, one kind of mortal molecule might have encountered its long-lived angelic catalyst, sparking a self-sustaining chemical reaction.
Small changes in the surrounding conditions would then produce slightly different molecular structures. These shadowy reactions, which Nobel prizewinning biochemist Christian de Duve called "protometabolism", might eventually have produced RNA, one of the ancient building blocks of life. These must have been robust and repeatable chemical reactions, not some one-off chance combination of circumstances, said de Duve.
According to Solomon, the angels and mortals game demonstrates that even a low concentration of the right chemicals could produce a robust self-sustaining reaction, eventually leading to the proliferation of life. What might seem unlikely, given the scarcity of chemicals, needs only the smallest of chances in order to take root on Solomon's playing board.
There have been other attempts to explain how the complexity of chemical life arose. Stuart Kauffman of the Santa Fe Institute in New Mexico has produced simulations that allow a variety of chemicals to react together,in which he has seen complex chemistry emerge. But Kauffman achieves complexity from a multitude of substances and interactions, whereas Solomon believes his angel and mortals simulation starts with the most basic components. "We have very simple reactions-A catalysing B-and we get a lot of complexity." Having shown that the chemical adaptability can come for free, Solomon plans to put in more substances" to see how different islands would learn to exploit different compositions and compete with each other.
Another area that could benefit from the angel and mortals simulation is immunology.Here, the emergence of population islands is not such good news.Solomon has been working with Israeli immunologists to explain how HIV can survive in what should be impossible circumstances. Here the simulation is inverted: antibodies attach themselves to virus particles, which allows immune cells to mop them up. An antibody has to have just the right sequence to grab hold of a particular strain of the virus, so the immune system generates antibodies at random until one fits. Then a flood of similar antibodies are produced, obliterating that viral strain.
But HIV mutates rapidly. You can imagine strains of virus wandering around in an abstract genetic space as they mutate. Every strain will eventually encounter a deadly antibody, and then the game's up for that strain. But Solomon's simulation shows that, if the rate of mutation is fast enough, islands of virus proliferate. "We find using this model that the immune system wins in every confrontation with an particular HIV strain," says Solomon, "but as the mutant strains become more numerous, the immune system eventually collapses under their collective pressure.
But never mind the origins of life or the tenacity of death. What about more important questions, like how to make pots of money? Think of the game board as an array of investment opportunities, with the angels representing the profitable ones. Dollar bills flock around these sites, and when they meet the angels they give birth to baby dollars. In the gaps between the profitable investments, money lies dead and decaying. Solomon's simulation shows that financial markets don't need intelligent investors to work. Money can survive and even proliferate simply by being multiplied in good investments and reduced in bad ones.
Solomon's ignorant agents can teach us something about robotics too. Chris Melhuish of the University of the West of England in Bristol says he has seen unconscious adaptation occurring in very simple robot systems. In some cases, he says, complex behaviour can be a manifestation of simple rules.

Melhuish thinks this kind of characteristic could help roboticians create swarms of cheap, small "dumb" robots that move through and act on their environment. Ideally, he would have them perform their small tasks without being encumbered with senses, computing power or communication devices.
These little robots might herd around more complex "angelic" control units with more senses and intelligence, which give them new life by performing repairs a providing power. Solomon's simulation shows that these higher beings could be few and far between, and the dumb mortals could be very One Humanoid Escapee dumb indeed. So it won't cost a fortune to assemble an army of robotic cleaners that will clean your car and dust your house, self-sufficient and supervised by the foreman from heaven. Then you'll have to find some other mindless activity to pursue while musing on the meaning of life.

"I wasn't walking with angels....oh sweet miracle of life"-RUSH

The idyllic antithesis - child-like wholeness - is symbolised by the most powerful baby of all,the Divine Child. This archetype is present in most cultures in one form or another. For example, Christian iconography features the Divine Child as a cherub or angel. The ancient symbology of the alchemists featured the regally robed figure of the Divine Child to indicate the Philosopher's Stone - which represented identification with the eternal, and the god within. The Divine Child connects us with the part of ourselves that is not constrained by our persona or ego. The Divine Child may appear in dreams as vulnerable yet inviolable, reminder and guardian of our most precious hopes, aspirations, impulses and instincts. ["Wake up to your dreams" -Joan Hangar]
Second of the holy choirs are the cherubim. This term derives from the Hebrew kerubh, translated to mean, 'the ones who intercede.' In mythology cherubs have most commonly become known as guardians of sacred places. In a biblical context, the casket which held the Ark of the Covenant had two golden cherubs guarding it and two were also said to guard Eden. Elsewhere, representations of these heavenly figures can be seen at the entrances to temples and other places of worship. In Sumer and Babylon, cherubim equivalents became monstrous beings, again guarding sacred places and even kings. In the Near East, the cherubim evolved into the fabulous jin, or genies as we now know them, who are of course guardians of lost knowledge and power.[Predictions July 97]


Michael Brooks is a freelance science writer based in Sussex

Further reading

Solomon's homepage is
More artificial life at





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New Scientist 6 May 2000 File Info: Created 17/6/2002 Updated 15/11/2014 Page Address: