Where Do We Come From?
Robert Shapiro

My son had many things to play with during his childhood, but one was special. Her name was Frizzle. She was a ball of inquisitive fur several inches long that the pet store classified as a gerbil. Frizzle spent much of her time in the brief few years of her life in exploring the multichambered residence that we had prepared for her, and then in trying to escape from it. When she died, we missed her.

For various reasons, I had no animal pet when I was young, but for a time, I attempted to nourish a small cactus plant. Its activities were less interesting than those of a gerbil; it grew slightly, but made no effort to escape. Yet I was saddened when it turned gray and drooped, and I realized that it had lost the struggle for survival.

We all learn at an early age how profoundly living things change when they die. We also recognize that the living things we know are a small part of a larger surrounding universe of things like water, rocks, and the moon that are not, and have never been, alive. This wisdom belongs to our own time, however. For centuries, many observers, including skilled scientists, did not recognize that dead things do not become alive. They felt, for example, that river mud could give rise to serpents, and raw meat could give birth to worms in a process called spontaneous generation. Only through many carefully controlled experiments, culminating in a brilliant series carried out by Louis Pasteur in the nineteenth century, was this theory disproven. We now recognize that life comes only from previously existing life, like a flame that can be divided, and spread, but once extinguished, can never be rekindled.

How then did life first come into existence, on this planet or anywhere else that life may exist in the universe? Many religions and some philosophies avoid the problem by presuming that life, in the form of a deity or other immortal being, has existed eternally. An alternative view can be found in science, where we look for natural answers in preference to supernatural ones and turn to another possibility: that life arose from nonlife at least once, sometime after the creation of the universe.

To learn about life's origins, we obviously cannot rely upon human records or memories, and must turn instead to the evidence stored in the earth itself. Those data are left as fossils in sediments whose age can be deduced from the amount of radioactivity remaining in surrounding rocks. For example, an unstable isotope of potassium is sealed into a volcanic rock when it solidifies from lava. Half of this isotope decays every 1.3 billion years, with part of it converted to the stable gas argon, which remains trapped in the rocks. By measuring the amounts of the remaining potassium isotope and the trapped argon, and performing a simple calculation, we can determine the age of the rock.

The fossil record tells a marvellous tale of the rise of life. It starts three and a half billion years ago with single-celled forms that resemble bacteria and algae, and leads up to the overwhelming variety of living creatures, including ourselves, that are present today. Earth itself is only one billion years older than the earliest record of life discovered thus far. If we were to compare Earth's age to that of a sixty-year-old man, then the fraction of Earth's existence needed for life to appear could be compared to the time needed for the man to reach puberty. The geological time occupied by all recorded human history would be equivalent to the last half- hour or so of the man's existence. Unfortunately, the record of geology peters out beyond three and a half billion years ago. No rocks remain that tell us anything about the way in which the first bacteria-like creatures came into existence. This process remains a profound puzzle.

A human being is so much more than a bacterium, though. If we can understand the evolutionary process that produced ourselves from one-celled creatures, and the developmental changes that convert a one-celled fertilized egg into a multicelled adult, then why is it difficult to understand how a bacteria could form from nonliving matter?

To appreciate this problem, we must explore the structure of life as it exists today. Obviously, this topic can fill many volumes, but here I wish to draw out a single thread that serves to distinguish life from nonlife: Living things are highly organized. I have chosen a word that is familiar; some scientists prefer terms like negative entropy, but basically, the idea is the same. By using organized, I mean to describe the quality that distinguishes the complete works of William Shakespeare from a series of letters struck at random on a typewriter, or a symphony from the sound one gets by dropping dishes on the floor. Clearly, things produced by the activities of life, for example, Shakespeare's works, can also be organized, but things unconnected with life, like a rock on the surface of the moon, are much less so. A bacterium, when compared with nonliving matter, is still very organized. The comparison between a dust particle and a bacterium would then be similar to the match of a random string of letters to a Shakespeare play.

Some scientists who have thought about life's origins have believed that this gap in organization between living and nonliving matter could be closed by random chance alone, if enough tries were made. They have drawn great encouragement from a famous experiment devised by Stanley Miller and Harold Urey. Miller and Urey showed in 1953 that certain amino acids could be formed very easily when electrical energy is passed through a simple mixture of gases. These amino acids are building blocks of proteins, one of life's key components. If key chemicals can arise so readily, can the rest of life be far behind?
To support the theory that pre-biotic methane may have played an important role in the development of life during the Hadean, the Miller-Urey experiments were conducted in the 1950s. These experiments tried to replicate the environmental conditions of the primitive Earth to see if organic compounds would form. When methane was included, the experiments showed that complex reduced carbon compounds, such as amino acids, were formed by non-biological processes. This seemed to prove that complex organic molecules can build up from very simple organic molecules, such as methane. The precise gas mixture used in the Miller-Urey experiments has since fallen out of favor with scientists as the most likely pre-biotic atmosphere. Still, methane could have been a component of the Earth's early atmosphere.

Unfortunately, life is vastly more organized than the "prebiotic" chemical mixtures formed in Miller-Urey-type experiments. Imagine that by random strokes on the typewriter you type the words to be. You might then be reminded of the famous line: "To be, or not to be: that is the question." A further jump of imagination might lead you to the idea that the remainder of Hamlet could then emerge from the random strokes. But any sober calculation of the odds reveals that the chances of producing a play or even a sonnet in this way are hopeless, even if every atom of material on Earth were a typewriter that had been turning out text without interruption for the past four and a half billion years.

Other thinkers, including a number of religious people, have argued that the formation of life from nonliving matter by natural means is impossible. They cite the Second Law of Thermodynamics, and claim that the formation of organized matter from disorganized matter is forbidden by it. But the Second Law applies only to sealed-in (closed) systems. It does not forbid nonliving chemicals on Earth to absorb energy from an outside source such as the sun and becoming more organized. The gain in organization here would be balanced by a greater loss of organization in the sun, and the Second Law would thus be satisfied.

When chemical systems absorb energy, however, they usually use it to heat themselves up, or to form new bonds in ways that do not lead to any gain in organization. We don't know the key recipe-the set of special ingredients and forms of energy that could lead chemical systems up the ladder of organization on the first steps to life. These circumstances may be quite rare and difficult or, once you have grasped the trick, as simple as brewing beer or fermenting wine.

How can we find out more? One way would be to run more prebiotic experiments. Many have been run, of course, but they usually have searched for the chemicals present in life today, rather than seeking to identify the process of self-organization. It isn't likely that the highly evolved biochemicals of today-proteins, nucleic acids, and other complexities-were present during the first faltering steps to life. What we need is more understanding of how simple chemical substances such as minerals, soaps, and components of the air will behave when exposed to an abundant and continuing supply of energy, such as ultraviolet light. Would the material simply turn into a tar or dissipate the energy as heat? Most of the time this would happen, and little of importance would have been learned. But perhaps, if the right mixture were chosen, complex chemical cycles would establish themselves and continue to evolve. If so, we would have gained an important clue about the beginning of life. Some experiments of this type could be carried out in undergraduate and even high-school laboratories, as they would not require complex and costly equipment. This area remains one where amateurs could make a significant contribution to fundamental science.

Another scientific approach to seeking our origins is very expensive, but it would provide great excitement and inspiration along the way. In the past generation, we have developed the ability to explore our solar system, but not good enough reasons to ensure that this is done. By that I mean objectives that would capture the attention of the public and motivate them to support the costs, rather than ones of interest only to scientists deeply immersed in their specialities. The solar system offers a dazzling array of worlds, each containing different chemical systems that have been exposed to energy for billions of years. Some of them may have developed in the direction of organization. By discovering a system that has started on such a path, even a different path from the one followed on our own planet, we may get vital clues about the principles involved in self-organization and the nature of our own first steps. A treasure hunt of this type among the worlds surrounding our sun might or might not discover early forms of life, but would certainly put some life back into our space program.

"Where do we come from?" In my title, I put the origin of life in terms of a question of location, as a child might do. Some scientists have argued that life started elsewhere, then migrated to planet Earth. Even if this were so, that fact would still not solve the central question, which is one of mechanism: "How did we come to be?" Location may be critical, though, in another way: To learn how we started, even if it happened here, we may have to venture out into the greater universe that awaits us.

ROBERT SHAPIRO is professor of chemistry at New York University. He is author or coauthor of over ninety articles, primarily in the area of DNA chemistry. In particular, he and his coworkers have studied the ways in which environmental chemicals can damage our hereditary material, causing changes that can lead to mutations and cancer. His research has been supported by numerous grants from the National Institutes of Health; the Department of Energy; the National Science Foundation; and other organizations.

In addition to his research, Professor Shapiro has written three books for the general public. The topics have included the extent of life in the universe (Life Beyond Earth, with Gerald Feinberg); the origin of life on earth (Origins: A Skeptic's Guide to the Creation of Life on Earth); and the current effort to read the human genetic message (The Human Blueprint).

RI Lecture 2013:Where do I come from?


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How Things Are: A Science Toolkit for the Mind
Edited by John Brockman and Katinka Matson

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