Life, it might be argued, is the distinguishing feature of all organisms and may most usefully be thought of as involving various kinds of complex systems of organization providing individual organisms with the ability to make use of those energy sources available to them for both self maintenance and reproduction. Underlying this deceptively persuasive definition, however, lie those persistent traditional problems inherent in the search for an essential, distinctive substance characteristic of all forms of life.
Additionally, as evolution theory makes clear, there is the problem of borderline instances, organisms of which it is not easy to say whether or not they may be defined as being alive. One such case is that of the virus. Viruses are the smallest, simplest living things, smaller than bacteria, and the cause of some of the deadliest diseases known to humanity. They are composed chiefly of nucleic acid wrapped in a coat of protein and are able to multiply only from within living cells.
As with all other organisms, the virus depends for its ability to obtain energy and carry out the other processes necessary to sustain life, upon its stock of DNA, the hereditary material that makes up the genes, the “instructions” that determine the traits of every living organism. What is interesting about viruses, however, is that their genetic stock is very meagre indeed, so much so that reliance upon it alone cannot enable them to survive. Nonetheless, viruses do persist from one generation to the next, as if they were alive.
How this is managed, as it clearly is in both plants, animals and human beings, bears importantly upon the ways in which “life”, at least in the case of viruses, may legitimately be defined. Advances in molecular genetics and the consequent growth in understanding of the developmental processes of organisms have tended to lead to the consensus, among both scientists and philosophers, that no explanatory principles important to the life sciences are likely to be found anywhere but within those sciences themselves.
Vitalist notions that there is some feature of living organisms that prevents their natures being entirely explained in physical or chemical terms only have, as a consequence, been increasingly eclipsed. In vitalist doctrine, this mysterious additional feature may be argued to be the presence of a further entity, such as a soul, although it may also be explained as having to do with the existence in specific organisms of sets of conditions derived from their complexity and necessitating some form of life force or animal electricity injected in some way into inanimate bodies in order for them to become alive.
In his expression of vitalism, Aristotle puts forward, in both De Anima and De Generatione, the view that the life of an animal consists in its psyche , thus offering a principle of explanation which determines the morphological development of an organism in terms of teleological causation. Although vitalism is currently perceived as having been largely overwhelmed by modern scientific thinking, there remain problems of some magnitude to which scientific solutions or explanations have yet to be found.
These may be felt to support the criticism often levelled at science, that it is descriptive rather than analytical, that it explains how certain phenomena occur, but not why. One problem of this type, by way of example, concerns the difficulty of understanding how different levels of description and explanation of the same thing, such as those of psychology, biology and chemistry, may be said to relate to each other.
The issue of whether or not solutions to these and other deep metaphysical problems must be conceded to lie beyond the contingent limits of human cognitive power continues to absorb some philosophers. Although representing a fairly extreme position, such scepticism has been, for example, a central preoccupation of the recent work of Colin McGinn [Problems in Philosophy: The Limits of Inquiry, Oxford, 1993]. To arrive at an agreed understanding of the ways in which meanings may be derived from specific life-contexts, when the subject of the analysis remains less than fully understood, is problematic.
It is clearly unsound to argue that there is some proposition to do with meaning, either different in each case or uniquely common to all, the existence of which may be presupposed in every investigation. As Aristotle makes clear at the beginning of his Nichomachean Ethics, the transitions between, for example, the following statements are also clearly fallacious: “There is something which is the meaning of all our activities” “Each of our activities has a meaning” There is a purpose common to all of our activities” It may be, in other words, that, although it is clearly important, for most human beings at least, to think of their lives as having some intrinsic purpose, this may not be the case, except insofar as that purpose is self defined. The meaning of life, in other words, may be what an individual decides that it will be. Equally, it may also be the case that the question as to whether or not life has any meaning is itself not meaningful.