Origins of Life
Young children often pose the most interesting questions. “Why are we here?” is one of them. And this question can take on many forms. One of them is “Why is there anything at all?” Another is “Why am I alive?” or “Why am I me?”
These questions are closely connected to central questions in natural science. In my opinion, there are three, and all three are concerned with origins. After all, “Why is there X?” is closely related to “Where does X come from?” So what are the most interesting puzzles about origins? I would say: the origin of matter; the origins of life; and the origin of consciousness.
To put it in the form of questions: “Where did matter come from?” “How did matter become alive?” and “How did living beings develop the capacity to ask these three questions?” Fortunately, modern science is now making inroads toward providing at least some answers to some aspects of these questions, while suggesting more precise ways to pose the questions.
The first question concerns cosmology, the branch of astrophysics that studies the origin of the universe. In this area, enormous progress has been made. Thanks to very precise observations, from space as well as from the ground, the general Big Bang picture has been validated empirically as an accurate description of how the universe evolved, from a very early time, going back to at least the first microsecond after the current universe was born.
The theory of the Big Bang has a number of free parameters, most of which are now known to high accuracy. To give you a sense of the precision of those details, we can take the age of the universe. Only twenty years ago, we knew that the value was somewhere between ten and twenty billion years. However, now we know that the Big Bang happened 13.80 billion years ago, with an estimated error of less than 0.04 billion years. This implies a remarkable accuracy of better than 0.3 percent.
Of course, knowing what happened during the nearly fourteen billion years after the birth of the universe, from the first microsecond on, doesn’t mean that we know what happened deep within that first microsecond, nor does it mean that we know how and why the universe came into being. But at least we are now able to formulate the question of the origin of the universe in a much more precise way, having pushed back the uncertainty into the very first fraction of a second. With respect to the question of the origins of life, we are nowhere near anything resembling the kind of progress that cosmology has made. And the question of the origin of consciousness is even more of a mystery.
Why so? Well, we know what matter is, and the only question is where it came from. We sort-of think we know what life is, but surprisingly, we can’t agree on a definition (see, for example, http://en.wikipedia.org/wiki/Life#Definitions). In terms of consciousness, we can study electrical and chemical processes in the brain, arriving at a third-person objective description of what living matter in a brain does. But does that tell us what consciousness is? The first-person experience of consciousness is so different from any third-person description of changes in brain states that it begs the question of how and why the two are related, even if we had complete information about how they are correlated.
Coming back to the origins of life question, we can formulate it as follows. On the early Earth, how did the transition from chemistry to biology take place? Most likely, there was no specific point at which one could say: this combination of molecules in this setting was not yet alive, while in the next combination somehow life had arrived. A more reasonable guess is that there was a more gradual transition, or series of transitions, at the end of which most everyone would agree that life had been formed. Hence, the term “origins” is considered more appropriate than “origin.”
So how did geochemistry transform into biochemistry? There are three leading scenarios. As a mnemonic at least, they parallel the three human interests in shelter, food, and procreation. One school argues that it began with cell walls, forming the equivalent of little test tubes, providing shelter within which more and more complex chemical reactions could take place, building up more and more complex molecules, without their being watered down within the surrounding environment.
Another school asserts the notion that metabolism came first, in the form of a primitive network of processes that consumed food and energy, leading to modest growth of whatever the first living organisms were on Earth. A third school maintains that replication was the initial step, in the form of what is called an RNA world, where particular RNA molecules began to copy themselves before attracting more complex processes, including forms of simple metabolism, to join in the making of simple cells.
For me, there are two related questions that are at least as interesting as the question of the origins of life. One is the question “What is life?” As I mentioned earlier, nobody has ever succeeded in given a convincing definition of life, as opposed to non-living matter. You could rephrase this as “What is the essence of life?” An analogy here might be helpful.
If you had asked James Watt, in 1875, to describe the essence of steam engines, he might have given an answer in terms of pistons and wheels and pullies, or perhaps, more abstractly, in terms of pressure exerted by steam caused by heating water with fire.
It took fifty years before Sadi Carnot gave a much more abstract description (known as the Carnot cycle), in which he showed not only how steam engines actually work, but also what the potential limits were on the efficiency of steam engines. After another quarter century, the concept of entropy was introduced by Rudolf Clausius, and yet another twenty-five years later, Ludwig Boltzmann showed how the macroscopic notion of entropy is related to microscopic molecular motion.
It took a full century to reach deep insight into the principles underlying the steam engine, from Watt to Boltzmann. My guess is that it may easily take a century from James Watson and Francis Crick’s discovery of the molecular structure of DNA to arrive at a truly fundamental understanding of the nature of living matter, on a par with insights provided by equilibrium thermodynamics for human-made engines.
A further sharpening of the question of the origins of life is the question “Why life?” Whether or not, and how, life originally came into being on Earth, and possibly on other planets, there is a still deeper question of why life is possible at all. What is it about matter, as a collection of protons, neutrons, and electrons, with some relatively simple interactions between them, that given enough time it can spontaneously give rise to living organisms? Is there something specific to protons and neutrons that they can form the ninety-two elements of the periodic table that occur in nature? Is there something special about carbon chemistry that has allowed life as we know it?
In more general terms, would something resembling life originate in other systems that are large enough in terms of space and time, starting with a few simple building blocks and some simple rules governing their interactions? Could such spontaneous emergence even be a generic property of large enough relatively simple systems?
A physicist would phrase these questions in terms of phase transitions, such as the freezing of water into ice. In that case, the disordered motion of H2O molecules in water spontaneously gives rise to the much greater form of order present in ice or in snow crystals.
Similarly, would a large enough simple system show spontaneous changes, from initial disorder to the order of living organisms? Could the origin of life be seen as a kind of phase transition, from simplicity to complexity, with organic chemistry just one specific example?
These are the kind of questions that I am currently exploring, together with some of the visitors in my Program in Interdisciplinary Studies, who often stop by for a few months, weeks, or days at a time. Several of them are affiliated with a new research center at the Tokyo Institute of Technology’s Earth-Life Science Institute (ELSI) (www.elsi.jp/), which I helped found last year as one of the Principal Investigators on the original proposal to the Japanese Ministry of Education. ELSI is now recruiting up to twenty new postdocs with backgrounds in astrophysics, geology, chemistry, biology, physics, or any other area related to the origins of life.