Biology is the science of the living world. One of the big questions it has to answer is, how does the living process differ from inanimate things? Mankind has always tried to answer this question. The history of ideas and the current answer supplied by biology is described by Ernst Mayr in This is Biology (Harvard University Press, 1997).
The earliest ideas ascribed a supernatural essence, spirit, to inanimate as well as animate objects - humans, animals, plants, rivers, mountains, etc. This universal animistic view of nature gradually passed away, but the idea that living things, particularly human beings, possess a spirit vigorously persists to this day.
The arrival of the scientific revolution saw a sharp decline in magical thinking culminating in Rene Descartes' (1596-1650) claim that all organisms except humans are simply machines. The idea of a world working with mechanical precision sprang from the work of Galileo, Kepler and Newton, who used mathematics to explain the cosmos.
From that time until the 20th century, when a new understanding arose, two competing schools of thought, called physicalism and vitalism, vied with each other to explain the nature of life. Physicalism contended that life was not really different from inanimate matter and could be fully understood by the laws of physics and chemistry. Vitalism proposed that the living process depends on a unique vital force.
The traditional method of scientific investigation of any system is to break the system into its component parts, study each part in isolation, and put the lot back together again, thereby achieving an understanding of the whole. This reductionist approach has worked very well in the physical sciences and, so far, in biological science. Physicalism sought to understand the living process by achieving a physico-chemical understanding of all the simplest component parts of biological organisms.
Vitalism was largely a reaction against physicalism. Despite much effort, the nature of the vital force was never identified. There is a tendency to dismiss vitalism as being unscientific, but it performed a valuable function by highlighting fatal flaws in the physicalist's arguments, in particular the contention that all aspects of the living process can be predicted by physics and chemistry.
Organicism is a philosophy of biology, developed this century. According to this school, both physicalism and vitalism were both partly right. Organicism takes account of the several unique attributes of living organisms. It adopts a holistic approach and contends that a living organism is more than the sum of its parts. The simplest components of a living organism are atoms - mainly carbon, hydrogen, oxygen and nitrogen. These atoms combine together in organisms to form the various bio-molecules (e.g. amino acids, nucleotides, etc.) in ways that can be explained by chemistry and physics. These bio-molecules in turn combine together to form giant macromolecules (e.g. proteins, nucleic acids, etc.). This behaviour can also be explained and predicted by chemistry and physics. These macromolecules assemble themselves into the membranes, organelles, and other structures that together make up the basic unit of life, the cell.
Animal cells associate together to form organs, organs co-operate with each other to form systems and the systems together form the overall animal. The further away you move from the level of the macromolecule, the weaker the direct explanatory and predictive power of chemistry and physics. When you consider how an organism is assembled from its component parts it is clear that, as complexity of organisation increases, unexpected new properties appear that cannot be predicted by examining isolated component parts of a functioning unit. Thus, an alien intelligence with an understanding of physics and chemistry but with no experience of biological life, would never predict the emergence of a living cell as a possible result of the interaction of biological macromolecules. This is partly why a reductionist approach alone will never completely explain the living process.
Living organisms also differ from the inanimate world in going through recurring cycles of conception, development, ageing and death. This sequence of developments is teleonomic (goal-directed). The biological function of death is to continually replace individuals with variations on the theme, ensuring that maximum variety is always present to meet new challenges produced by the environment.
Living organisms, unlike inanimate things, have a dual nature: a genotype and a phenotype. The genotype is the genetic information which controls and specifies much of the nature of the living organism. This blueprint is inherited from generation to generation and the information it currently bears is conditioned by its history of experience over the past 3.5 billion years. The phenotype of a living organism is its physical form. The phenotype and the genotype interact with each other in the complex symbiotic dance that is the living process.
The reductionist method of science was developed to investigate the inanimate world. Its application to the living world has also produced spectacularly successful results, e.g. the discovery of the nature and mechanism of action of the genetic material. However, in order to fully understand the nature of living organisms we have to think in a more sophisticated way. Unfortunately, far too many biologists still think in an exclusively reductionist mode and suffer from "physics-envy". The ultimate dream of physics is to explain everything in the universe with a few equations. While it may be possible to go a long way towards this goal in explaining the inanimate world, I don't think this approach will do for the living world.
While the bottom-up approach continues to be important in biology, it needs to be increasingly supplemented with a top-down mode of thinking. We may already have learned most of what we can learn about the forest by studying the sawdust.
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.