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Robert May
ANY ATTEMPT TO FORMULATE A DEFINITION THAT DISTINGUISHES LIFE FROM NON-LIFE REPRESENTS A FALSE DICHOTOMY
exobiology panel, has tried to achieve this. He proposed one of the descriptions in Lahav’s list as a “working definition” for life in the context of space exploration: “Life is a self-sustained chemical system capable of undergoing Darwinian evolution.” This succinct and widely cited metric combines three distinct characteristics. First, any form of life must be a chemical system. Accordingly, computer programs, robots or other electronic entities are not alive. Life also grows and sustains itself by gathering energy and atoms from its surroundings – the essence of metabolism. Finally, living entities must display variation. Natural selection of more fit individuals inevitably leads to evolution and the emergence of more complex entities. This NASA-inspired definition is probably as general, useful and concise as any we are likely to come up with – at least until we discover more about what is actually out there. Armed with such a definition, we can imagine that our planet’s earliest life may have been vastly different from anything we know today. Many experts suspect that the first living entity was not a single cell as we know it, for even the simplest cell incorporates astonishing complexity. That first life form probably did not use DNA, given the intricacies of the genetic code, nor did it necessarily rely on proteins, the chemical workhorses of cellular life. As a geologist trained in the ways of rocks, my favourite hypothesis is that the earliest entity to fit NASA’s trial definition might have been a molecular coating on rock surfaces. Such “flat life” would grow as a layer only a few nanometres thick, exploiting energy-rich mineral surfaces while slowly spreading like lichen from one rock to the next. If such life still exists on Earth today, yet lacks diagnostic www.newscientist.com
061118_F_3_Life.indd 49
DNA or proteins, how would we know? In spite of such well-intentioned efforts to define life, any attempt may be doomed to failure for the simple reason that the transition from the non-living to the living world was inherently gradual. French anthropologist Claude Lévi-Strauss, who investigated the mythologies of many cultures, identified a deep-seated human tendency to reduce complex situations to oversimplified dichotomies: friend and enemy, heaven and hell, good and evil. The history of science reveals that scientists are not immune to this mindset. In the 18th century, the Neptunists, who favoured a watery origin for rocks, fought with the Plutonists, who favoured heat as the causative agent. Both, it turns out, were more or less right. A similar contentious and ultimately misleading dichotomy raged between 18thcentury catastrophists and uniformitarians, the former espousing a brief and cataclysmic geological history for Earth and the latter holding that geological processes are gradual and ongoing. More recently, once-doctrinal distinctions between plants and animals or single-celled and multicellular organisms have become similarly blurred. Any attempt to formulate an absolute definition that distinguishes between life and non-life represents a similar false dichotomy. The first cell did not just appear, fully formed. Rather, life must have arisen through a sequence of emergent events – diverse processes of organic synthesis followed by molecular selection, concentration, encapsulation and organisation into various molecular structures. The emergence of self-replicating molecules of increasing complexity and mutability led to molecular evolution through the process of natural selection, driven by competition for limited raw materials. What today appears as a yawning divide between non-life and life obscures the fact that the chemical evolution of life occurred in this stepwise sequence of successively more complex stages. When cells emerged, they quickly consumed virtually all traces of the earlier stages of chemical evolution. “Protolife”, a rich source of food, was wiped clean by voracious cellular life. Our challenge, then, rather than to define life in absolute terms, is to establish a progressive hierarchy of steps leading from a prebiotic Earth enriched in organic molecules to cellular life. The nature and sequence of these steps may vary in different environments, and we may never know the exact sequence – or sequences – that occurred on Earth. Yet many of us suspect that the chemical path has a similar, inexorable direction on any habitable planet or moon.
ROBERT MAY Application of the physical and biological sciences has made today arguably the best of times: we live longer and healthier lives, food production has doubled in the past 35 years and energy subsidies have substituted for human labour, washing away hierarchies of servitude. But the unintended consequences of these well-intentioned actions – climate change, biodiversity loss, inadequate water supplies, and much else – could well make tomorrow the worst of times. The significant breakthrough we really need is better understanding of human institutions, particularly of the impediments to collective, cooperative activity in which all individuals pay small costs to reap large group benefits. Darwin recognised the evolution of cooperative behaviour as one of the most important unsolved problems of his day. We have made relatively little progress since then. Perhaps the social scientists of 2056 will have succeeded in combining the rigour of the “hard” (that is, easy) sciences with the thoughtful introspection of the humanities to solve this problem. I certainly hope so. Robert May holds a joint professorship at the University of Oxford and Imperial College London
LISA RANDALL With the advent of the Large Hadron Collider, the next 50 years should tell us more about the underlying nature of matter and how elementary particles acquire their mass. These insights might provide information not just about particles, but possibly about the underlying nature of space-time. On a theoretical level, tantalising hints of space breaking down at short distances and time breaking down at singularities tell us that fundamentally, space and time are not what we think. Physicists are just beginning to address these issues. Progress should occur in domains where field theory (which combines quantum mechanics and special relativity), cosmology (which studies the evolution of the universe), and quantum gravity (which may or may not be string theory) overlap and reach the edges of their applicability. Lisa Randall is professor of physics at Harvard University
18 November 2006 | NewScientist | 49
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exobiology panel, has tried to achieve this. He proposed one of the descriptions in Lahav’s list as a “working definition” for life in the context of space exploration: “Life is a self-sustained chemical system capable of undergoing Darwinian evolution.” This succinct and widely cited metric combines three distinct characteristics. First, any form of life must be a chemical system. Accordingly, computer programs, robots or other electronic entities are not alive. Life also grows and sustains itself by gathering energy and atoms from its surroundings – the essence of metabolism. Finally, living entities must display variation. Natural selection of more fit individuals inevitably leads to evolution and the emergence of more complex entities. This NASA-inspired definition is probably as general, useful and concise as any we are likely to come up with – at least until we discover more about what is actually out there. Armed with such a definition, we can imagine that our planet’s earliest life may have been vastly different from anything we know today. Many experts suspect that the first living entity was not a single cell as we know it, for even the simplest cell incorporates astonishing complexity. That first life form probably did not use DNA, given the intricacies of the genetic code, nor did it necessarily rely on proteins, the chemical workhorses of cellular life. As a geologist trained in the ways of rocks, my favourite hypothesis is that the earliest entity to fit NASA’s trial definition might have been a molecular coating on rock surfaces. Such “flat life” would grow as a layer only a few nanometres thick, exploiting energy-rich mineral surfaces while slowly spreading like lichen from one rock to the next. If such life still exists on Earth today, yet lacks diagnostic www.newscientist.com
061118_F_3_Life.indd 49
DNA or proteins, how would we know? In spite of such well-intentioned efforts to define life, any attempt may be doomed to failure for the simple reason that the transition from the non-living to the living world was inherently gradual. French anthropologist Claude Lévi-Strauss, who investigated the mythologies of many cultures, identified a deep-seated human tendency to reduce complex situations to oversimplified dichotomies: friend and enemy, heaven and hell, good and evil. The history of science reveals that scientists are not immune to this mindset. In the 18th century, the Neptunists, who favoured a watery origin for rocks, fought with the Plutonists, who favoured heat as the causative agent. Both, it turns out, were more or less right. A similar contentious and ultimately misleading dichotomy raged between 18thcentury catastrophists and uniformitarians, the former espousing a brief and cataclysmic geological history for Earth and the latter holding that geological processes are gradual and ongoing. More recently, once-doctrinal distinctions between plants and animals or single-celled and multicellular organisms have become similarly blurred. Any attempt to formulate an absolute definition that distinguishes between life and non-life represents a similar false dichotomy. The first cell did not just appear, fully formed. Rather, life must have arisen through a sequence of emergent events – diverse processes of organic synthesis followed by molecular selection, concentration, encapsulation and organisation into various molecular structures. The emergence of self-replicating molecules of increasing complexity and mutability led to molecular evolution through the process of natural selection, driven by competition for limited raw materials. What today appears as a yawning divide between non-life and life obscures the fact that the chemical evolution of life occurred in this stepwise sequence of successively more complex stages. When cells emerged, they quickly consumed virtually all traces of the earlier stages of chemical evolution. “Protolife”, a rich source of food, was wiped clean by voracious cellular life. Our challenge, then, rather than to define life in absolute terms, is to establish a progressive hierarchy of steps leading from a prebiotic Earth enriched in organic molecules to cellular life. The nature and sequence of these steps may vary in different environments, and we may never know the exact sequence – or sequences – that occurred on Earth. Yet many of us suspect that the chemical path has a similar, inexorable direction on any habitable planet or moon.
ROBERT MAY Application of the physical and biological sciences has made today arguably the best of times: we live longer and healthier lives, food production has doubled in the past 35 years and energy subsidies have substituted for human labour, washing away hierarchies of servitude. But the unintended consequences of these well-intentioned actions – climate change, biodiversity loss, inadequate water supplies, and much else – could well make tomorrow the worst of times. The significant breakthrough we really need is better understanding of human institutions, particularly of the impediments to collective, cooperative activity in which all individuals pay small costs to reap large group benefits. Darwin recognised the evolution of cooperative behaviour as one of the most important unsolved problems of his day. We have made relatively little progress since then. Perhaps the social scientists of 2056 will have succeeded in combining the rigour of the “hard” (that is, easy) sciences with the thoughtful introspection of the humanities to solve this problem. I certainly hope so. Robert May holds a joint professorship at the University of Oxford and Imperial College London
LISA RANDALL With the advent of the Large Hadron Collider, the next 50 years should tell us more about the underlying nature of matter and how elementary particles acquire their mass. These insights might provide information not just about particles, but possibly about the underlying nature of space-time. On a theoretical level, tantalising hints of space breaking down at short distances and time breaking down at singularities tell us that fundamentally, space and time are not what we think. Physicists are just beginning to address these issues. Progress should occur in domains where field theory (which combines quantum mechanics and special relativity), cosmology (which studies the evolution of the universe), and quantum gravity (which may or may not be string theory) overlap and reach the edges of their applicability. Lisa Randall is professor of physics at Harvard University
18 November 2006 | NewScientist | 49
7/11/06 4:00:05 pm