Is Biology Reducible to Chemistry?

IS BIOLOGY REDUCIBLE TO CHEMISTRY? GRAEME K. HUNTER* Introduction What is it, if anything, that distinguishes living organisms from non-living objects? This question has interested humans since the beginnings of recorded history, and, no doubt, before. Throughout the history of science and philosophy, opinions on the uniqueness or otherwise of living systems have pitted materialists against vitalists, reductionists against organicists, atomists against holists. This schism also finds echoes in a number of contemporary scientific controversies, including creationism (can life arise from a chemical soup?), the Gaia hypothesis (is the Earth a living organism ?), and the Human Genome Project (to what extent is an organism defined by its DNA sequence?) . This question ofwhether there is something qualitatively different about living systems is an example of the philosophical problem of reduction. In its broadest sense, this concerns whether all natural phenomena, from sociology to chemistry, can ultimately be explained in terms of physical laws. The reductionist view is encapsulated in Ernest Rutherford's famous characterization of all the non-physical sciences as "stamp collecting." Similarly , Francis Crick has written that "The ultimate aim of the modern movement in biology is to explain allbiology in terms of physics and chemistry " [I]. The alternative (anti-reductionist) view is that there are phenomena that only emerge at higher levels of organization, such as complex living systems , and can only be understood in terms of that level. In 1944, at the dawning of the era of molecular biology, Erwin Schrödinger wrote: "from all that we have learned about the structure of living matter, we must be prepared to find it working in a manner that cannot be reduced to the ordinary laws of physics" [2]. A similar view has been articulated more recently by the physicist Philip Anderson: "at each level of complexity en- *Division of Oral Biology, Faculty of Dentistry, University of Western Ontario, London, Ontario N6A 4Cl, Canada.© 1996 by The University of Chicago. All rights reserved. 0031-5982/96/3904-0965$01.00 130 Graeme K. Hunter ¦ Is Biology Reducible to Chemistry? tirely new properties appear, and the understanding of the new behaviours requires research which I think is as fundamental in its nature as any other. . . . Psychology is not applied biology, nor biology applied chemistry " [3], The question of whether biology is "applied chemistry" reappeared at the highest levels of scientific eminence in 1986. While delivering the first Medawar lecture at the Royal Society, philosopher of science Karl Popper stated that "biochemistry could not be reduced to chemistry" [4]. The gauntlet was taken up by the biochemist Max Perutz, who subsequently published a refutation of Popper's view [5]. It is interesting to note that the reductionist and anti-reductionist positions do not appear to correlate with academic disciplines. That is to say, philosophers and scientists are to be found on both sides of this debate; likewise physicists and biologists. It is also clear that term "reduction" is a term with many shades of meaning: the varieties of reduction described include ontological, theoretical, epistemological, physical, constitutive, explanatory , stepwise, precipice, micro-, macro-, and objective. Interestingly, when one looks at what philosophers and philosophically minded scientists actually say about the nature of living systems, there appears to be little or no disagreement on the major issues. Thus, a reconciliation of the reductionist and anti-reductionist positions may be possible. In what follows, an approach towards such a reconciliation will be suggested. In order to do this, however, it is first necessary to clarify certain concepts that have in the past often confused these issues. Vitalism Science arises out of myth. Early humans invoked spirits in clouds and mountains in order to explain the occurrence of natural phenomena such as thunder and earthquakes. This animist tradition—Jacques Monod's "old covenant" between man and nature [6] —was only laid to rest during the Renaissance, to be replaced by the mechanistic world-view of Galileo and Newton. The explanatory power of the new physics was such that Descartes could postulate that all biological processes (except human consciousness) were mechanical in nature, and Laplace's all-knowing demon could plot the fate of every atom in the universe. However, many still believed that living processes...