Can life be reduced to physics

It is clear from the foregoing that the microscopic components of an organism consist of a society of molecules, each apparently responding blindly to the physical forces that happen to act upon them at that point in space and time, yet somehow cooperating and integrating their individual behaviour into a coherent order. With the marvellous advances of modern molecular biology, we can now see in detail the clash of ideas that dates from that ancient conflict: Democritus' atomism and Aristotle's holistic teleology. How can individual atoms, moving strictly in accordance with the causal laws of physics, responding only to local forces that happen to be produced by neighbouring atoms, nevertheless act collectively in a purposeful, organized and cooperative fashion over length scales vastly in excess of intermolecular distances? This is Monod's 'profound epistemo-logical contradiction' referred to above.

In spite of the fierce mechanistic leanings of modern biologists, such a contradiction inevitably surfaces sooner or later if an attempt is made to reduce all biological phenomena to molecular physics. Thus geneticist Giuseppe Montalenti writes:5

Structural and functional complexity of organisms, and above all the finalism of biological phenomena, have been the insuperable difficulty, the insoluble aporia preventing the acceptance of a mechanistic interpretation of life. This is the main reason why in the competition of Aristotelian and Democritean interpretations the former has been the winner, from the beginning to our days.

All attempts to establish a mechanistic interpretation were frustrated by the following facts: (a) the inadequacy of physical laws to explain biological finalism; (b) the crudeness of physical schemes for such fine and complex phenomena as the biological ones; (c) the failure of'reductionism' to realize that at each level of integration occurring in biological systems new qualities arise which need new explanatory principles that are unknown (and unnecessary) in physics.

Much of the debate between biological reductionists and their opponents takes place, however, at cross purposes. Reductionistic biologists take the position that once the basic physical mechanisms operating in a biological organism have been identified, life has been explained as 'nothing but' the processes of ordinary physics. They argue that because each component of a living organism fails to reveal any sign of peculiar forces at work, life has already effectively been reduced to ordinary physics and chemistry. Since animate and inanimate matter experience exactly the same sort of forces, and since many of life's processes can be conducted in a test tube, any outstanding gaps in knowledge are attributed solely to technical limitations. As time goes on, it is claimed, more and more details of the workings of organisms will be understood within the basic mechanistic paradigm.

It is worth pointing out that the claim that animate and inanimate matter are both subject to the same physical forces is very far from being tested in practice. What the biologist means is that he sees no reason why the sort of molecular activity he studies should not be consistent with the operation of normal physical forces, and that should anyone decide to investigate more closely the biologist would not expect any conflict with conventional physics and chemistry to emerge.

Let us nevertheless grant that the biologist may be right on this score. It is still far from the case, however, that life has then been 'explained' by physics. It has, rather, simply been defined away. For if animate and inanimate matter are indistinguishable in their behaviour under the laws of physics then wherein lies the crucial distinction between living and nonliving systems? This point has been emphasized by the physicist Howard Pattee, who has had a longstanding interest in the nature of life. He writes:6 'We do not find the physical similarity of living and nonliving matter so puzzling as the observable differences.' To argue the latter away 'is to miss the whole problem'.

The mystery of life, then, lies not so much in the nature of the forces that act on the individual molecules that make up an organism, but in how the whole assemblage operates collectively in a coherent and cooperative fashion. Biology will never be reconciled with physics until it is recognized that each new level in the hierarchical organization of matter brings into existence new qualities that are simply irrelevant at the atomistic level.

Scientists are coming increasingly to recognize that there is no longer any basis in physics for this sort of reductionism. In Chapter 4 it was explained how non-linear systems can display chaotic, unpredictable behaviour that cannot be analysed into the activity of component subsystems. Writing about chaos in an issue of Scientific American a group of physicists pointed out that:7

Chaos brings a new challenge to the reductionist view that a system can be understood by breaking it down and studying each piece. This view has been prevalent in science in part because there are so many systems for which the behaviour of the whole is indeed the sum of its parts. Chaos demonstrates, however, that a system can have complicated behaviour that emerges as a consequence of simple, nonlinear interaction of only a few components. The problem is becoming acute in a wide range of scientific disciplines, from describing microscopic physics to modelling macroscopic behaviour of biological organisms . . . For example, even with a complete map of the nervous system of a simple organism ... the organism's behaviour cannot be deduced. Similarly, the hope that physics could be complete with an increasingly detailed understanding of fundamental physical forces and constituents is unfounded. The interaction of components on one scale can lead to complex global behaviour on a larger scale that in general cannot be deduced from knowledge of the individual components.

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