What is Life?:How chemistry becomes biology

by Pross, Addy

  So we have here an intriguing phenomenon—biologists, the scientists who devote themselves to the study of living systems, and who possess a deep appreciation of life’s complexity, having successfully probed many of its key components, remain mystified by what life is, and physicists, with their deep understanding of nature’s most fundamental laws, are no less confused. Both continue to struggle with the nature of life question and we can only conclude that the 3,000-year ‘what is life’ riddle remains that—a riddle. Let us then begin our journey of discovery by briefly considering each of the characteristics that makes life special, so different to inanimate matter, and discuss what makes those characteristics so strange, so very strange.

  Life’s organized complexity

  Living things are highly complex. In fact the very first line in Richard Dawkins classic text The Blind Watchmaker begins with the remark that we animals are the most complicated things in the universe.2 That attention-grabbing line on its own is enough to drive home the realization that we animals must be something very special. But what is it about us living things that makes us so complicated, or, to use the more scientific word, so complex? And what does the term ‘complex’ actually mean? At the risk of sounding circular, one could say the term ‘complexity’ is itself complex, not readily defined, and attempts over the years to quantify the concept have not proven too successful, at least not within a biological context. Let us then focus on the crucial aspect of complexity as it pertains to bioslogy—the highly organized nature of living things.

  In the non-living world it is easy to find examples of complexity. The shape of a boulder is certainly complex and in that case the complexity derives from its irregular shape. To describe its shape with precision would require information—the more irregular the shape, the more information would be required. The physical location of each point on the boulder’s surface would need to be specified in some manner. The important point, however, is that we understand that the boulder’s irregularity, the source of its complexity, is arbitrary. It could have been any one of a zillion other irregular shapes and the boulder would still be a boulder. It is not the particular irregularity of that boulder that makes it a boulder. By contrast, in the living world complexity is not arbitrary, but highly specific. Even the slightest structural change to that organized complexity may have dramatic consequences. For example, even a single change in a human’s DNA sequence, one out of 3 billion units, may potentially lead to thousands of genetic diseases, such as sickle cell anaemia, cystic fibrosis, and Huntington’s disease. Small changes to life’s complex structure may well undermine the viability of that living system, and in extreme cases the living system may be living no longer.

  What is quite extraordinary and hard to comprehend is that such organized complexity extends to entities as small as a bacterial cell, just one thousandth of a millimetre across. In many respects the bacterial cell operates like a highly sophisticated nano-scale factory, nano-scale meaning the factory components are of molecular size, that is, of the order of one millionth of a millimetre in length. That nano-factory involves a highly complex but integrated network of chemical reactions, which extract energy from the environment, storing it in a number of different chemical forms for use in the biosynthesis of essential cellular building blocks; the control and regulation of the cellular machinery to ensure proper function; the list goes on and on. The cell is not just a master chemist, but a master physicist as well. That microscopic entity uses every mechanical trick in the tradesman’s book—pumps, rotors, motors, propellers, even scissors to snip here and there, all at nano-scale, to ensure cellular functions are carried out expeditiously, as required by the cell’s ‘purpose’.

  But that undisputed complexity, so different to inanimate complexity, is puzzling and raises two immediate questions. How is the organized complexity of the cell maintained, and how did it come into being? Organized complexity and one of the most fundamental laws of the universe—the Second Law of Thermodynamics—are inherently adversarial. We won’t go into the Second Law in any detail at this stage, but a very simple (and limited) expression of the Second Law is the statement that organized systems spontaneously tend toward disorganization, toward disorder. Nature prefers chaos to order, so disorganization is the natural order. Take a pack of cards in some highly ordered sequence—say four aces, followed by four kings, then by four queens, and so on, down to four twos—shuffle the deck and the sequence invariably becomes disordered. You’ll almost certainly end up with some random sequence. The likelihood of some other highly ordered sequence being formed is very slight. That’s the Second Law in action. The state of my desk at any point in time is further proof, if it were needed. No matter how often I tidy my desk, it always seems to quickly revert to its preferred disorganized state. Within living systems, however, the highly organized state that is absolutely essential for viable biological function is somehow maintained with remarkable precision. There is even a biological term for the phenomenon whereby that organized state is maintained—homeostasis, from the Greek meaning ‘standing still’.

  So how is the cell’s organized complexity maintained, if a central law of physics and chemistry is constantly operating to undermine it? The answer to this first question is relatively easy, at least within the context of the Second Law: the living cell is able to maintain its structural integrity and its organization through the continual utilization of energy, which is in fact part of the cell’s modus operandi. That’s why we have to eat regularly to survive—to furnish the body with the necessary energy to enable the body’s regulatory mechanisms to maintain life’s organized homeostatic state. That also explains how my desk gets to be tidy occasionally—I expend energy now and then to restore a semblance of order whenever my desk has become too disordered to be functional. So there is no thermodynamic contradiction in life’s organized high-energy state, just as there is no contradiction in a car being able to drive uphill in opposition to the Earth’s gravitational pull, or a refrigerator in maintaining a cool interior despite the constant flow of heat into that interior from the warmer exterior. Both the car driving uphill and the refrigerator with its cold interior can maintain their energetically unstable state through the continual utilization of energy. In the car’s case the burning of gasoline in the car’s engine is the energy source, while in the case of the refrigerator, the energy source is the electricity supply that operates the refrigerator’s compressor. In an analogous manner, energetically speaking, the body can maintain its highly organized state through the continual utilization of energy from some external source—the chemical energy inherent within the foods we eat, or, in the case of plants, the solar energy that is captured by the chlorophyll pigment found in all plants. No fundamental problem there.

  But how the initial organization associated with the simplest living system came about originally is a much tougher question. Despite the widespread view that Darwinian evolution has been able to explain the emergence of biological complexity, that is not the case. Darwinian evolution is able to broadly explain how a simple single-cell living organism—what one might call the microbial Adam—eventually became an elephant, a whale, or a human. But Darwinian theory does not deal with the question how that primordial living thing was able to come into being. The troublesome question still in search of an answer is: how did a system capable of evolving come about in the first place? Darwinian theory is a biological theory and therefore deals with biological systems, whereas the origin of life problem is a chemical problem, and chemical problems are best solved with chemical (and physical) theories. Attempting to explain chemical phenomena with biological concepts is methodologically problematic for reasons we will discuss subsequently, and in some sense that approach may have been partly responsible for the conceptual dead-end the subject seems to have found itself in.

  Significantly, Darwin himself explicitly avoided the origin of life question, recognizing that within the existing state of knowledge the question was premature, that
its resolution at that time was out of reach. So the question of how the first microscopic complexity came into being remains problematic and highly contentious. Did a cellular precursor to that exquisitely complex miniature factory that is the living cell come together purely by chance, by the various bits and pieces randomly linking up in precisely the right manner? Not very likely. To draw on an analogy popularized by Fred Hoyle, the well-known astronomer (though famously misapplied), the likelihood of such an event would be similar to that of a whirlwind blowing through a junkyard and assembling a Boeing 747. Life’s organized complexity is strange, very strange. And how it came about is even stranger.

  Life’s purposeful character

  There is another facet to the organized complexity of living systems that has been strikingly evident to humankind for thousands of years—life’s purposeful character. That purposeful character is so well defined and unambiguous that biologists have come up with a special name for it—teleonomy. The ‘teleonomy’ word was introduced about half a century ago to distinguish it from the ‘teleology’ word with its cosmic implications, and we will have more to say about how these terms relate to one another in chapters 2 and 8. At this point let us simply note that teleonomy, as a biological phenomenon, is empirically irrefutable. The term simply gives a name to a pattern of behaviour that is unambiguous—all living things behave as if they have an agenda. Every living thing goes about its business of living—building nests, collecting food, protecting the young, and, of course, reproducing. In fact, within the biological world that’s how we broadly understand and predict what goes on. We understand a mother nurturing her offspring. We know better (or should know better) than to step between a mother bear and her cub. We understand two males competing for a female; we understand a stray cat rummaging through a trash bin. We intuitively understand the operation of the biological world, including, of course, all human activity, through life’s teleonomic character.

  In the non-living world, by comparison, understanding and prediction are achieved on the basis of quite different principles. No teleonomy there, just the established laws of physics and chemistry. You throw a ball into the air and you want to know where it will land? The precise landing point is not calculated by considering the ball’s purpose. The ball has no purpose. Only Newton’s laws of motion will provide the answer. You mix some chemical compounds together and you want to know whether they will react and what materials are likely to form? You consider and apply the appropriate chemical rules, depending on the nature of the problem, and you come up with a prediction. No purpose, no agenda—just inviolate laws of nature. The notion of purpose within the inanimate world was laid to rest with the modern scientific revolution of the seventeenth century.

  The very existence of teleonomy however, leads us to a strange, even weird, reality: in some fundamental sense we are simultaneously living in two worlds each governed by its own set of rules—the laws of physics and chemistry within the inanimate world and the teleonomic principle that dominates the biological world. Indeed, given the existence of two distinct worlds we find ourselves interacting quite differently with each of those worlds. Consider our interactions within the inanimate world. We move from one place to another as required, we try to keep warm when it is cold, to keep dry when it rains, we build a physical enclosure to live in to protect ourselves and to facilitate life’s activities. We learn to climb up slopes despite the gravitational force, to generate fire for cooking, to manufacture tools for improved function, to plug a hole in a leaking roof, to avoid physical injury, and so on. All of our interactions with the inanimate world are based on the recognition that there are certain laws of nature, described primarily by the physical sciences, which govern the manner in which the universe functions. Understanding those laws helps us to keep out of trouble, and, even better, enables us to take advantage of nature’s modus operandi, thereby allowing us to further life’s goals more effectively. In fact that is the essence of technology—creating systems that exploit nature’s laws in a beneficial manner.

  Our interactions with the living world, however, are of a quite different kind and are much more complex. As we have already noted, the living world is teleonomic—all living creatures are busy furthering their agenda, and in doing so they must take into account the particular agenda of other living beings. Accordingly, living things create a web of interaction with other living things, making many of our actions mutually dependent. Consider us humans. We communicate and deal with members of our immediate family, with our work colleagues, with other members of our society in an endless series of interactions—by spoken and written word, more subtly without words, by gestures. Some of these interactions are cooperative in nature, some competitive. Ordering a cappuccino at the local café or going to the hairdresser exemplify cooperative interactions, while bargaining in the market over the price of some article or fending off an intruder are competitive interactions. Our lives involve endless interactions of both types as we individually pursue our ‘purpose’ and get on with life’s goals. We also continually interact with a wide range of non-human life forms. Our need for sustenance is satisfied by feeding on other living creatures, both animal and vegetable, and we protect ourselves against the life forms that threaten us, whether multicellular creatures—bears, sharks, snakes, mosquitoes, or spiders—or from single-celled creatures—bacteria of endless variety. Many non-human interactions are cooperative—the pet dog that we feed which provides companionship and warns us of intruders, the billions of bacteria in our gut to which we happily provide room and board, and who return the favour by assisting us with our digestion and more.

  We are so used to this dual state of affairs—matter that exists in both living and non-living forms—that much of what has been said here is glaringly obvious and very much taken for granted. Familiarity breeds acceptance, if not contempt. But if I were to tell you that on Mars all material forms obeyed one set of principles, yet on Venus they followed another different set, we would all be startled. How could that be? Two material forms broadly following two distinct sets of principles? The fact that here on Earth there exist two material forms that are distinct in character, are governed by different organizational principles, which comfortably coexist, and in fact continually undergo material interchange—non-living matter is continually transformed into living matter, and vice versa—demands some explanation. How can this stark duality in the nature of matter exist and what does it signify?

  Before going any further let me be unequivocal and make one point perfectly clear: it goes without saying that within the teleonomic world the same underlying rules of physics and chemistry that govern the inanimate world are still operative. No doubt about that. When a person falls off a ladder the law of gravity is operative in exactly the same way as when a bag of sugar falls off a shelf. But in many respects those natural laws are of little or no use when applied to living systems. The law of gravity and the Second Law of Thermodynamics aren’t particularly helpful when you are arguing with a neighbour over some property issue, or when seeking to renew an expired licence, or when fending off an aggressive dog. Within the living world those same laws have little predictive value—they are certainly operative but appear to be of only secondary importance. The underlying rules of physics and chemistry have somehow been taken hostage and overwhelmed by another more dominant set of principles. If you want to predict the actions of a crouching lion preparing to pounce on an unsuspecting zebra, a mother tending to her young, a lawyer planning to sue you on behalf of an aggrieved client, or indeed any other teleonomic action, the laws of physics and chemistry are of little use. Neither a physicist nor a chemist will be able to offer a useful prediction. If you want to make a prediction about some impending event in the living world, go ask a biologist, psychologist, economist, lawyer, or other teleonomic specialist, depending on the nature of the question.

  Not surprisingly then, much of human knowledge and understanding involves the teleonomic, rather than the physic
ochemical world. Consider for a moment any large university with its many faculties, each dedicated to a particular field of enquiry. The faculties of humanities, commerce, and law (and to a lesser extent, the faculty of medicine), are dedicated to the teleonomic world with its many manifestations. There is just one faculty—the faculty of natural sciences—that dedicates itself specifically to the study of the natural world, and even within this faculty we find the department of biological sciences grappling awkwardly with the teleonomic reality, uncertain as to how the paradox of a dichotomic world can and should be resolved. That, then, is the undeniable, yet so far inexplicable reality—the laws of nature, as primarily articulated in the subjects of physics and chemistry, offer few insights into the predominantly teleonomic world of which we find ourselves very much a part.

  Intriguingly, despite the irrefutable teleonomic character of living systems, some biologists still have difficulty in coming to terms with that extraordinary character. The troublesome ‘purpose’ word, now sanitized and repackaged into the scientifically acceptable ‘teleonomy’ word, still leaves many modern biologists squirming uncomfortably. The scientific revolution’s overthrow of 2,000 years of teleological thinking has left biologists anxious and unwilling to accept even the slightest vestige of that earlier, misplaced way of thinking. But there is no denying the teleonomic principle. The evidence supporting it is simply overwhelming, all around, literally endless, and cannot simply be dismissed out of hand.