Читать книгу Astrobiology - Charles S. Cockell - Страница 21

Speaking unscientifically, we might all agree that life seems at first glance to be different from non-life. Without any in-depth analysis, many people intuitively think that life is unpredictable, complex, and, in a certain undefined way, full of energy. This is the perception that occurred to the ancients. Almost all their attempts to explain life revolved around ways to separate, if you will, life from non-life. It is also certainly true that the birth of monotheistic religion, such as Christianity, encouraged a general idea that life has a special place in the Universe and that it is categorically different from non-life. The underlying motive for this was almost certainly encouraged by a desire to separate animals, and particularly humans, from non-life. This perceived exalted position of humans would be consistent with the discomfort felt by many people when Charles Darwin's The Origin of Species convincingly suggested that we all share animal ancestors and that our closest relatives include apes.

However, long before the major monotheistic religions emerged around 2000 years ago, humans had already convinced themselves that “life” was categorically different from “non-life,” and the challenge was to find what that difference was. Greek philosopher Empedocles (c. 494–434 BCE) proposed a model in which everything in the Universe is made of four different materials: “elements” of water, air, earth, and fire. He did not call them elements, but rather “roots.” Different types of matter are formed by different mixtures of these roots. The mixtures account for all the characteristics of matter.

Democritus (c. 460–370 BCE) (Figure 2.1) advanced the idea that all matter is made of indivisible “atoms.” This idea was certainly radical, but it did not equate with the atoms we understand in modern science. First, his atoms were indivisible. Second, different atoms had different characteristics that aligned with the matter that they formed. For example, water atoms were slippery, and air atoms were diffuse and airy. Seen from a modern perspective, Democritus's atoms are more like our modern concept of molecules. In this view, Democritus explained life as being matter that had “fiery” atoms that imbued it with a “soul.” Here we can see an example of the assumption that life contained something material that separated it from all other types of matter. This idea would, and still does, prove difficult to shake off.

Figure 2.1 Democritus. Ancient Greek philosopher. He proposed an early atomic theory of matter.

Source: Reproduced with permission of The Heinrich Heine University of Dusseldorf, http://www.phil-fak.uni-duesseldorf.de.

Nevertheless, lurking behind his atomic theory was the important concept, now referred to as “materialism,” that life was mechanistic, an idea that would be picked up in the seventeenth century by philosopher René Descartes (1596–1650), who famously considered animals to be essentially machines.

Democritus's idea of the “soul” was advanced by Greek philosopher Aristotle in a form of philosophy called “hylomorphism.” The philosophy, yet again, is underpinned by a desire to find a way to explain the difference between living things and non-life. All material in the Universe was made of matter and form. In this theory, matter was the stuff of everything in the Universe and would align with our modern idea of matter. However, mixed in with this matter was a substance called “form.” The form was the “soul.” The soul could be used to explain the different cognitive capacities of living things. The vegetative soul is found in plants and allows them to grow and reproduce. The animal soul allowed animals to move and feel things. The rational soul, reserved for humans, allowed consciousness and reasoning. This substance, the soul, allowed for a categorical difference between life and non-life, but it also allowed for a gradation in cognitive capacities of organisms that provided a safe, and superior position, for humans.

Aristotle's ideas encouraged a wider idea that persisted throughout the Middle Ages all the way into the nineteenth century. One might even claim that remnants of this “hunch” persist to this day. This is the idea of “vitalism,” that life has some sort of force or energy that distinguishes it from non-life. Vitalism especially gained credence when the true atomic structure of matter was understood. The idea that elements were constructed from identical subatomic constituents, a concept that would later explain the structure of the Periodic Table, ended previous ideas that the difference between types of material could be explained by “fiery atoms” or other special atomic arrangements. Vitalism allowed for that special separation to persist between life and non-life. They could both be made of elements constructed of identical building blocks, but life had an extra force. This idea was picked up in the twentieth century by French philosopher Henri Bergson (1859–1941) in his 1907 book Creative Evolution in which he coined the term, “élan vital.” This “vital impetus” had no physical explanation, but various suggestions, such as special electrical energy, were in no short supply.