Introduction

At a public lecture at the Sorbonne in 1864, the renowned French scientist Louis Pasteur raised the fundamental philosophical question pertaining to the origin of life: can matter organize itself to form a living system? Pasteur answered this question with a decisive no. He was referring both to the emergence of life on the primordial Earth and to the possibility of “spontaneous generation” – the formation of living organisms out of matter here and now. Life, Pasteur believed, was originally created by God and organisms are subsequently born only from parents.

Toward the end of the eighteenth century, the German philosopher Immanuel Kant had also pondered the question of the nature of biological organization and its emergence from matter. Unlike other physical objects, Kant noted, an organism is an interactive system in which parts and whole are reciprocally dependent. This circular, self-reproducing nature defines a living system and the critical question is whether we can understand the production of such an organized, functional whole in causal, materialistic terms.

For Kant, the idea of physical principles of self-organization, working mechanistically without any guiding plan and yet capable of producing an organized whole, was inconceivable. Hence, the very possibility of the emergence of life from matter seemed to him absurd. Although not sharing Kant's and Pasteur's convictions, most scientists toward the end of the nineteenth century nevertheless preferred not to deal with the origin-of-life problem.

When the “origin-of-life” issue is debated nowadays, the question most often asked is: How did the first cell originate? What sequence of processes could have given rise to the extraordinary complexity of even the most rudimentary living cell? Once such a cell was in place, the assumption is that metabolism and descent with modification could begin and the Darwinian selection process could get under way, generating over the course of aeons the vast profusion of natural kinds, living and extinct, that we know. But what sort of selection principles, working on what sort of materials, could have sufficed in the first place to build up the kind of intricate structure that even the smallest functioning cell requires? In short, how did the living come from the non-living in the first place?

In earlier centuries, the transition from non-life to life would have seemed unproblematic, indeed entirely commonplace. It would have appeared obvious that living comes from non-living in the world of nature all the time: maggots develop in decaying flesh, tiny worms appear in rotting fruit, and so on. At the lowest levels of living complexity, matter (it seemed) could generate life unaided. Only with the advent of the microscope and finally the experiments of Pasteur was it shown that this kind of spontaneous generation was only apparent: no real transition from non-living to living actually occurred in it. So how did life begin?

The search for and discovery of extraterrestrial life, especially an independent origin of life, raise interesting philosophical issues (most or all of which can be connected to important practical issues), in at least three interrelated areas: (1) epistemology, (2) value theory (especially ethics), and (3) worldviews. This chapter samples a variety of views in these areas, touching slightly on some policy and theological connections, both of which are covered more extensively elsewhere in this volume.

The first section will explore epistemological areas such as (a) dealing with the limitation of knowing only one kind of biology, (b) challenges of discerning an independent origin of life, and (c) challenges for assessing the biological status of a region or entire planet. The ethical considerations of the second section will explore (a) the role of an independent origin of life vs. interplanetary transport, (b) ethical views ranging from anthropocentric to cosmological, and (c) potential policy implications. The third section will touch briefly on basic worldviews that revolve around (a) randomness and chance (an “accidental” universe), (b) purpose and meaning (a deliberate universe), and (c) a “bootstrapped” universe in which meaning and purpose emerge in the universe through valuing cultural beings (a “cultural cosmos”).

Epistemology

Extraterrestrial life poses unique challenges to the boundaries, application, and confidence in our knowledge. Some interrelated epistemological questions to consider are: (1) How can we deal with the limitations of knowing only one kind of biology?

Introduction

Astrobiology has life at its core: Where does life come from? Where is it going? Are we alone? While it includes the search for extraterrestrial life – the very bit that has so captured the public's attention – it uses life on Earth as its reference point. Of course this probably has less to do with philosophy, and more to do with practicalities. After all, there is only one place that we know with certainty contains life, and most likely an indigenous biota at that. So, planet Earth remains the reference point. Thus, a search for life elsewhere, even in our own solar system, must include an understanding of the known range of life on Earth. And, even before that, an understanding of what we mean by “life.”

Understanding the range of current life on Earth, and mapping it to current environments in the solar system, is only a start as it lacks the element of time. Life on Earth may have been substantially different when it arose around about 4 billion years ago because the environmental range on Earth was dramatically different. Similarly, the climatic conditions forecast for a billion or so years into the future are bleak for much of life as we know it, including ourselves. Without intervention, the Sun as we know it will not even exist.

Introduction

There has been a lively discussion recently about the science and ethics of “terraforming” Mars. The high level of interest is a result of spacecraft discoveries about Mars combined with the realization that humans are effectively warming the Earth and wondering if they can, and should, do the same on Mars. I suggest that terraforming is more appropriately called planetary ecosynthesis, and in this chapter I review the scientific studies of planetary ecosynthesis and the environmental ethics associated with instigating such global change on another planet.

Mars today is a cold, dry, frozen desert world on which not even the most hardy of Earth life could survive. Temperatures average −60°C and the pressure averages 0.6 kPa, over one hundred times less than atmospheric pressure at the surface of the Earth. As a result of the low pressure, and secondarily the low temperature, water is not liquid on the surface of Mars at any location or season. Strong solar ultraviolet radiation reaches the surface of Mars to complete the deadly mix of hostile environmental conditions.

But Mars has not always been this harsh. There is compelling evidence that early in its history Mars had stable liquid water on its surface. Presumably this phase of liquid water was associated with a higher pressure and somewhat warmer atmosphere.

The experimental investigation of life's origin commenced in earnest more than a half-century ago with the pioneering work of Miller, who synthesized many of life's molecular building blocks under plausible prebiotic conditions. Despite an initial euphoric sense that the origin mystery would soon be solved, scientists quickly realized that the transition from a geochemical to a biochemical world would not easily be deduced by the scientific method.

The great challenge of origins research lies in replicating in a laboratory setting the extraordinary increase in complexity that is required to evolve from isolated molecules to a living cell. The principal objective of this review is to describe some of the efforts by origin-of-life researchers to induce such increases in complexity. A unifying theme of these studies, and hence a useful organizing framework for this review, is the principle of emergence – the natural process by which complexity arises.

Emergence as a unifying concept in origins research

The origin of life may be modeled as a sequence of so-called “emergent” events, each of which added new structure and chemical complexity to the prebiotic Earth. Observations of numerous everyday phenomena reveal that new patterns commonly emerge when energy flows through a collection of many interacting particles.

The premise of my chapter is that history can be not only enlightening in itself but also significant in a variety of contemporary contexts. One clear example of this is in connection with the theological, ethical, and philosophical implications of the search for life, because these issues have been addressed again and again throughout history as the possibility of life beyond Earth has been raised. It is true that most of the historical debate has centered on extraterrestrial intelligence rather than microbial life. But at least part of the interest in the search for microbial life is that it is an indication of the prevalence of intelligence in the universe. This explains in part the uproar over the claims for nanofossils in the Mars rock in 1996 – much more was at stake than primitive life on Mars itself. This connection between microbes and intelligence is made especially in the popular mind, despite the fact that many evolutionists would argue that the gap between microbes and intelligence is greater than that between life and non-life. Thus, Peter Ward and Donald Brownlee have recently, and famously, argued that the universe may well be full of microbes, but not intelligence, making ours a “Rare Earth”. If this is true, the study of the implications of microbial life beyond Earth is all the more important.

Introduction

The origin of life has always been a topic charged with religious import. This chapter aims to survey briefly some origin-of-life ideas over time; first, if we look in detail at how the debate over life's origin played out between Darwin and his supporters, we will see a clear example of this. Note that I said Darwin's supporters, rather than his opponents. We expect a story about the new evolutionary science to include much heated objection from religious groups, for whom so many aspects of Darwin's theory produced problems. But a look at how divisive the issue was among the Darwinians themselves is an even more complex and enlightening story, perhaps of more relevance to scientists in their own work.

By the 1850s, William Benjamin Carpenter, Professor of physiology at the Royal Institution of London, believed, as did Herbert Spencer, that the vital force of living things was completely interconvertible with forces from non-living nature such as heat, electricity, kinetic energy, etc. However, also like Spencer and a number of others in the Darwinian camp, Carpenter believed that the conversion of heat or chemical energy into vital energy could only be accomplished through the agency of already living matter; in other words, that non-living matter could never organize itself into living matter capable of generating vital force. This served as a convenient theoretical barrier separating modern physiology and its ally, the new evolution theory, from the bête noir of spontaneous generation.