The Medea Hypothesis: Is Life on Earth Ultimately Self-Destructive?

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The Medea Hypothesis

Princeton University Press

Chapter One

From so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved. -Charles Darwin, On the Origin of Species, 1859

In the summer of 2007 I entered into a new experience: teaching the science of evolution to entering university students. Each of the nineteen students in my class, none older than eighteen years of age, started his or her first university class with some mixture of optimism and trepidation. Most, it turned out, wanted to be scientists. Yet in a series of short papers, most also readily admitted that while they had been well prepared in their high school classes in various mixtures of mathematics, chemistry, physics, and biology, virtually none had learned anything about what is variously labeled as evolutionary theory or, if one has a more creationist bent, Darwinism.

The reason for this omission was easily ascertained. Most high school teachers have stressful enough lives dealing with the daily traumas of teaching in U.S. high schools-why add extra drama by entering into one of the most emotionally charged of all subjects, evolution? Many a teacher has had the very unpleasant experienceof describing theories about human phylogeny and meeting an angry, fundamentalist parent soon thereafter. So the subject is largely ignored.

Unfortunately, when evolution is ignored, other allied sciences are ignored as well. Perhaps the most important of these deals with the origin of life. For reasons also obscure, one of the most perplexing and important of scientific questions-how life first appeared on Earth-is ignored in basic university biology courses and, if mentioned at all, is discussed in brief detail in a more advanced evolution course. But this seems curious, for how life first appeared and how it later evolved the ability to evolve were different processes. (As we shall see, the ability to evolve became an inherent property of Earth life, but surely only after the synthesis of life's building blocks.) The current modes of evolution involving genes on DNA, itself massed together in a chromosome, were a long way in the future when various snippets of amino acids were assembling into some proto-RNA molecule. Yet how life first came into existence is a viable field of study, and for want of any better place this topic is usually dealt with in an evolution class.

Thus, on my second day in class, I asked the assembled multitude to write me a short essay on the definition of life. The results were all over the map. While some honed in on chemical definitions, the majority leapt toward the metaphysical, imbuing life with a vast array of mystical properties, ranging from the minimal to truly godlike. What came through, however, was a fundamental property that does not usually make it into the textbooks but is at the heart of the arguments here: that life in the aggregate acts very differently from life as an individual. However, those imbuing life with properties over and above those of an individual saw those properties as inherently "good" and helpful to other life-with the sole exception of we humans, which were viewed rather guiltily as not following life's lead in making things better. I agree with my students' prescient sense that life as a whole acts differently from life as an individual. Where I disagree is about the ultimate effect of life on itself.

An analogy about this disconnect can be seen in the relationship between individual humans and the human race. Each of us lives our life, usually hoping for, and living in ways to create, as much happiness as possible. Many of us work diligently to reduce the environmental "footprint" of our existence. Yet in aggregate we are clearly changing the physical Earth, and changing conditions for both ourselves and other life. So too with "life": as an aggregate it has major effects on itself as well as the planet. This aspect of life might certainly help explain some of the behaviors proposed at the heart of my arguments here.

Let us begin this argument with the most minimal definition of life, followed by a definition of Earth life, for it is one of life's inherent properties that is the heart of the problem.

The question "What is life?" is deceptively simple, with no simple answer. Perhaps the most parsimonious answer is as follows: "All life forms are composed of molecules that are not themselves alive." This definition, as imprecise as it is, does hint at a deeper truth. At what level of organization does life "kick in"; in what ways do living and nonliving matter differ? Most who have thought deeply about what life could be, and what chemical forms it could take (Ward 2005), believe that Earth life is but one kind of possible life. But no one on this Earth can prove that there is any life beyond that of the Earth, and indeed one of the astonishments about life on Earth is not how diverse it is (which of course it is, at least at the level of species), but how poor the Earth is in the kinds of life. While those who worry about biodiversity rightly point out how the Earth is losing species, the reality is that there is only one kind of life on Earth-our familiar DNA/RNA life. E. O. Wilson's magnificent 1994 book, The Diversity of Life, could in reality be retitled One.

But what are the characteristics of life, and then Earth life, and why are these central to the arguments here? I will argue that one of the attributes that most experts equate with being "alive" is the ability for the entity to evolve in a way that would have been familiar to Charles Darwin, an evolution that now bears his name: Darwinian evolution. It is that aspect of Earth life (and perhaps all life, since the very number of stars in the cosmos make the presence of life beyond Earth as close to a certainty without being one as there could probably be) that, to many, is the source of Earth life's singular success. And yet how important is the behavior of an individual compared to the behavior-or, perhaps more properly, the effects-of the collective? My thesis is that the inherent property to evolve is also the source of the inherent "suicidalness" of life-a facet of what I will define as the Medea principle, to be posed and referred to here as a hypothesis.

Perhaps a better question than "What is life?" is "What does life do?" Physicist Paul Davies, who has pondered the "What is life?" question more than virtually any other thinker, listed the following:

Life metabolizes. All organisms process chemicals and in so doing bring energy into their bodies. But of what use is this energy? The processing and liberation of energy by an organism is what we call metabolism, and that is necessary to maintain internal order. Life has complexity and organization. There is no really simple life, composed of but a handful of (or even a few million) atoms. All life is composed of a great number of atoms arranged in intricate ways. But complexity is not enough; it is organization of this complexity that is a hallmark of life. Complexity is not a machine. It is a property. It is also something the life "does." Life reproduces. This one is obvious, and one could argue that a series of machines could be programmed to reproduce, but Davies makes the point that life must not only make a copy of itself, but also make a copy of the mechanism that allows further copying; as Davies puts it, life must include a copy of the replication apparatus too. Again, there are machines that allow life to copy itself, but the process is not that of a machine. Life develops. Once a copy is made, life continues to change; this can be called development. Again, this is a process mediated by the machines of life, but also involving processes that are quite un-machinelike. Machines do not grow, nor change in shape and even in function with that growth. Life is autonomous. This one might be the toughest to define, yet it is central to being alive. An organism is autonomous, or has self-determination. But how "autonomy" is derived from the many parts and workings of an organism is still a mystery, according to Davies. Yet it is that autonomy that again separates life from machine.

Finally, Davies noted: life evolves. According to Davies, this is one of the most fundamental properties of life, and one that is integral to its existence. Davies describes this characteristic as the paradox of permanence and change. Genes must replicate, and if they cannot do so with great regularity, the organism will die. Yet, on the other hand, if the replication is perfect, there will be no variability, no way that evolution through natural selection can take place. Evolution is the key to adaptation, and without adaptation there can be no life. Again, a process, not a machine.

Davies is far from alone in advocating that Darwinian evolution is a fundamental property of life, nor was he the first to do so. A decade before Davies so eloquently made these observations about life, the great Carl Sagan famously wrestled with the question of what life is. Unlike most others thinking about this topic, who were dealing only with life as it is found on Earth, Sagan came at the problem with a specific goal: he was interested in life beyond Earth, and at the time of his observations about life, in the mid-1970s, he was involved in several NASA missions involved in searching for such life, most famously the Viking missions to Mars. Sagan's definition of life, which was largely taken up by NASA and is still used to this day, sees life as a chemical system capable of Darwinian evolution, meaning that there are more individuals present in the environment than there is energy available, so some will die. Those who survive do so because they carry advantageous heritable traits that they pass on to their descendents, thus lending the offspring greater ability to survive.

The view that evolution is an inherent property of life has come to be called the evolutionist view. For instance, life has been defined as being a self-sustained chemical system capable of undergoing Darwinian evolution, as well as a self-replicating, evolving system based on organic chemistry, as well as a system capable of evolution by natural selection. Finally, life has been called a material system that undergoes Darwinian evolution.

So just what is "Darwinian evolution"? We should briefly describe its basic tenets before going any further. While Darwin is credited with a "theory of evolution," in fact he proposed two separate and testable hypotheses. The first is that all life on Earth came from a single common ancestor. Second, he proposed a principle of variation: that life reproduces to produce slightly different variants of the parent (as well as progeny that closely match the parent, or, in reproduction through cloning, forms that are genetically similar). But Darwin also noted that most "parents" produce more off spring than can live because of shortages of food, or shelter, or other necessities of life. Because of a surplus of offspring, in most instances some will perish. Those that survived did so in the long run-and indeed we are talking of many generations-because they had characteristics that made them in some way superior to others of their own species. These characteristics, such as larger size, which is a very common trend in evolutionary lineages, must also be "heritable"-that is, the characteristics have to be passed on to the next generation.

Darwin saw this competition as "survival of the fittest," and he gave the process the technical name "natural selection." Over the long run, the survivors would be those with characteristics (hereditable characteristics, that is, ones that can be passed on to the next generation and not just ones acquired during the life of the individual, such as a human sex change operation) lending the greatest "fitness," or ability to survive. Examples are many, such as the few giraffes with ten-foot-longnecks among a herd with seven-foot necks in places where the lowest vegetation is nine feet above the ground; the fastest-swimming fish in a lake where the predators can catch the slowest and even median-velocity swimmers. These survivors then pass on these successful characters to their offspring, and evolution has taken place.

Speciation, the formation of an entirely new species, is a larger-scale process. A species is deemed separate if it can no longer interbreed with its parent's populations. For new species to form, most commonly there must be geographic isolation of a subset of a smaller population into a new environment cut off from the larger population, one that has different challenges for survival. Over some generations these new environmental challenges would cause evolution of forms dissimilar enough that if the two populations should again come into contact, the two gene pools are now so different that breeding does not produce successful off spring.

Thinkers on the subject have come to agree that Darwinian evolution is certainly a key property of Earth life, or RNA/DNA life, and perhaps it is a necessary property of all life in the Cosmos.

DEFINING EARTH LIFE

With all the apparent diversity of life on Earth, all Earth life yet discovered shows a unifying characteristic-it all contains DNA. This is why I suggest that the true diversity of life on Earth is 1.

Composed of two backbones (the famous "double helix" described by its discoverers, James Watson and Francis Crick), DNA is the information storage system of life itself-the "software" that runs all of Earth life's hardware. These two spirals are bound together by a series of projections, like steps on a ladder, made up of the distinctive DNA "bases," or base pairs: adenine, cytosine, guanine, and thymine. The term "base pair" comes from the fact that the bases always join up: cytosine always pairs with guanine, and thymine always joins with adenine. The order of base pairs supplies the language of life: these are the genes that code for all information about a particular life form.

If DNA is the information carrier, a single-stranded variant called RNA is its slave, a molecule that translates information into action-or in life's case, into the actual production of proteins. RNA molecules are similar to DNA in having a helix and bases. But they differ in usually (but not always) having but a single strand, or helix, rather than the double helix of DNA. Also, RNA has one different base from DNA.

RNA is tantalizing stuff. While indeed it is "hardware" in carrying amino acids to protein-building sites in the ribosomes, it is clear that some RNA has multiple functions, including information storage. There is an apparently important regulatory role played in eukaryotes by nonprotein-coding RNA, which is an example of RNA acting simultaneously as software and hardware.

DNA provided the answers to many of the mysteries of genetics, answering the question, once and for all, about what is a gene, for the nature of inheritance, from Darwin's time to the twentieth century, had remained a most vexing question. James Watson and Francis Crick made the great discovery-one that launched an enormous revolution in biology-and their great discovery was announced in a paper in the journal Nature that was but a single page long. Their finding was actually a model, not an experimental result, but the model had enormous predictive power. It became clear that a gene is made of DNA, and that one gene makes one protein. Watson and Crick proposed that one half of the DNA ladder serves as a template for re-creating the other half during replication. Each gene is a discrete sequence of DNA nucleotides, with each "word" in the genetic code being three letters long.

How does a gene specify the production of an enzyme? It was Francis Crick who suggested that the sequence of bases was a code-the so-called Genetic Code-that somehow provided information for the formation of proteins, one amino acid at a time. The information coded had to be read (transcribed) and then translated into proteins. That is where RNA comes in. Earth life uses twenty amino acids. Not nineteen. Not twenty-one. And always the same twenty! DNA codes for RNA, which codes for proteins, which are all made up of combinations of the twenty amino acids. This, then, the central dogma of molecular biology, may also be called a central characteristic of Earth life.

HOW EVOLUTION ARISES

Genes are the blueprints necessary to make Earth life's major structural and chemical partner: proteins. Proteins perform the various functions of the cell. A protein's action is determined both by its chemical constituents and by its shape. Proteins become folded in highly complicated topographies, and often their final three dimensions shape their actions.

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Excerpted from The Medea Hypothesis by Peter Ward Copyright © 2009 by Princeton University Press. Excerpted by permission.
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