Hist 606/ Phil 650
Prof. Stephen Brush
Does Biology Reduce to Physics?
A Look at How the Question Has Been Answered Through Time
The three possible answers are:
Physics, chemistry, biology. Historically these are accepted as the three major disciplines within the sciences. To the lay public, there is an unexamined acceptance that other broad sciences simply build on these three: geology is a special kind of physics, neuroscience a type of biology. But to the philosopher of science the ways in which various disciplines connect is not considered self-evident. One of the fundamental questions of the past century has been whether biology is in fact no more than examples of physicochemical laws carried out in a macroscopic environment. The question is asked whether biology reduces to physics.
To say that biology reduces to physics is to say that all the laws and/or facts of biology can be explained or replaced by laws and facts from physics. Looking at it from the other direction: if biology reduces to physics, then if one were somehow able to know correctly all the laws of physics, one could deduce all of biology as well. Biology would hold no unexpected surprises.
Toss a theory into an academic community and it will, of course, be supported, contradicted, torn apart, patched back together again, and remolded several times throughout the ages. Biological reduction has fared no differently.
The broad outlines of the arguments started in Ancient Greece. While the ancient philosophers did not couch their discussions in the same vocabulary--biology was not a defined science, reduction not a defined concept--they nevertheless divided into two basic camps on the issue. The Aristotelian vitalistic view held that living organisms were fundamentally distinct from inanimate objects. Living creatures have some special property that the lifeless world does not. On the opposite side was the Democritean mechanistic view, living beings are simply special cases of the atomic world, bound to inexorably follow the same atomic laws.
Mechanism and vitalism remained the two main camps on the subject up until the current century so they are worth describing in further detail. To some degree, the differing philosophies of the two men arise from their different understandings of cause and effect. Democritus allowed for only one type of cause and effect: material necessity. Certain situations necessarily led to certain outcomes, as defined by atomic structure and movement. Atomic laws ultimately caused everything. Aristotle, on the other hand, defined four types of causes, including the "final cause." The function of an object or organism is reason enough for it to come into being. While he noted that certain things did not have specific functions--the varying colors of people's eyes, for example--Aristotle saw the final cause as the most important cause in biological phenomena. Aristotle's view of life, therefore, incorporates a holistic higher purpose, as living creatures (and their attributess) all match some kind of Platonic ideal. Even today, the validity of teleology--the explanation of phenomena through their final causes--continues to play a role in the arguments for and against reduction.
To medieval philosophers, Democritus's view of life--relying solely on random accidents of atoms bumping into each other--was clearly an incomplete description for a world where we witness so many creatures with forms fitted to function. Mere chance didn't seem to adequately explain such harmony in the universe. Moreover, mechanism denied the role of G-d which was unacceptable in the religious medieval climate. With the onset of the Scientific Revolution, Western thinkers began to more comfortably embrace the notion that all phenomena could be explained by science. But that "science" was almost exclusively in the realm of the physical sciences. As Mayr puts it, "For the philosophers, from Bacon and Descartes to Locke and Kant, the physical sciences, and in particular mechanics, were the paradigm of science. The proper way to study the ntaural world, according to this view, was to define phenomena in terms of movements and forces that obeyed universal laws." Those scientists who did study living organisms therefore held a largely mechanistic view, believing their studies to be no different than the physical sciences being studied at the time. By the time of Lamarck and Cuvier in the late 1700s, biology came unto itself as a separate branch of the natural sciences. "Biology" covered the study of these organisms, which clearly had some inner organization that added up to a functioning whole. And the "whole" became as--if not more--important than its components. These scientists swung back closer to the Aristotelian viewpoint. But biologists did not limit themselves to the whole organism for long. By the mid-19th century biochemistry and cellular biology entered the discipline, bringing many scientists back around to the reductionist viewpoint that peeling away layer after layer of mechanisms would eventually lead one down to physics and chemistry.
Having made these broad generalizations about the fluctuations of the vitalistic and mechanistic viewpoints, let's pick the thread up in greater detail in the 19th century. By the beginning of the 1800s biologists had proven that chemical processes occurred in living organisms. This naturally gave rise to a whole host of questions, says Goodfield.
Given the obviously different properties of organisms and inorganic substances, what was the significance and importance of the physicochemical reactions going on within living things? Were these similar or only analogous in the two realms? What was the value--if any--of quantitative methods when applied to living organisms, and what was the relevance of the results obtained? What in fact did the physicochemical experiments tell us? Did organisms or did they not, conform to the laws of physics and chemistry? Should they or should they not, be studied with physicochemical techniques? And if the answers to the last two questions were to be "yes," then how could one account for those observable differences or properties which were the starting point of the very recognition of living organisms in the first place?
As represented by these questions, the relationship between biological and physicochemical phenomena had suddenly become much more complex. The two camps of Aristotle and Democritus no longer fully encompassed all the possible relationships between the two. For some time those who denied a completely mechanistic view were still called vitalists. But what was meant by the term was far from clear. Vitalists all believed that something fundamental distinguished life from non-life, but the nature of that constituent was debated.
Moreover, the various reductionist and antireductionist viewpoints could be (and still are) divided into two broad categories (though they certainly weren't done so consciously at the time) the methodological and the ontological, as named by Schaffner, Mayr and others,.
In the early 1800s, the concerns were mostly with the methodological issues. The questions centered around whether the experimental methods of the physical sciences even had a place in biology. Goodfield cites the physiologist M.F.X. Bichat at one antireductionist extreme,
One calculates the return of a comet, the speed of a projectile; but to calculate with Borelli the strength of a muscle, with Keill the speed of blood, with Lavoisier the quanitity of air entering the lung, is to build on shifting sand an edifice solid itself but which soon falls for lack of an assured base. This instability of the vital forces marks all vital phenomena with an irefularity which distinguishes the from physical phenomena remarkable for their uniformity. It is easy to see tha the scienc eof organised bodies shoudl be treated in a manner quite different form those which have unorganised bodies for object.
Most physiologists did acknowledge the need for physicochemical methods "but worried a great deal about the exact relevance of their results and the nature of the explanation they should be formulating." Determining just how much importance should be placed on these types of experiments had yet to be hammered out.
The methodological controversy at this basic a level--do physical and chemical experimental methods have a place in a biological laboratory?--was left behind as the great tide of biologists simply rushed headlong into using those methods. The emphasis then switched to the ontological. The question began to focus on whether or not--and, if so, how--living organisms were fundamentally different from inorganic objects.
One of the earliest books to tackle the subject from an ontological viewpoint was Claude Bernard's Introduction to the Study of Experimental Medicine in 1865. Bernard put forth a theory that Schaffner classifies under the category "emergentism-in-principle." In the context of a living organism, there exist conditions such that physicochemical processes behave in a way that they do not outside of organic life. He says, "Physiologists and physicians must therefore always consider organisms as a whole and in detail at one and the same time, without ever losing sight of the peculiar conditions of all the special phenomena whose resultant is the individual." By conditions, Bernard meant physical conditions: pH, temperature, chemical constituents. The characteristics unique to life emerged from the particulars of this environment, which (due to such attributes as warm-bloodedness, for example) was not in equilibrium with the surrounding physical world. Today we perceive Bernard as an antireductionist--he states that life definitely has properties that non-life does not--but he was careful to distance himself from the vitalists of the day:
I should agree with the vitalists if they would simply recognise that living beings exhibit phenomena pculiar to themselves and unknown in inorganic nature. I admit, indeed, that manifestations of life cannot be wholly elucidated by the physico-chemical phenomena known in inorganic nature. . . I will simply say that if vital phenomena differ from those or inorganic bodies in complexity and apperance, this differnece obtains only by virtue of determined or detrminable conditions prpoer to themselves. So if the science of life must differ from all others in explanation and in special laws, they are not set apart by scientific method.
At the end turn of the century, Hans Driesch made one last great case for Aristotilian vitalism. He championed the idea that living entities were imbued with a special vital force or spirit (Driesch used Aristotle's word: entelechie) unique to the organismic world. He drew upon Aristotle's concept that a perfect "idea" of every organism exists before the organism comes into being. This ideal acts as one of Atisotle's final causes, creating that particular creature. The classic vitalist thesis was not embraced by scientists at the time and has not reared its head again within the scientific or philosophy community.
On the other hand a strict ontological reductionist viewpoint has not been wholeheartedly embraced recently either. At least not by philosophers. Dobzhansky says "Most biologists. . . are reductionists to the extent that we see life as a highly complex, highly special and highly improbable pattern of physical and chemical processes." But he does point out that this does not imply that all biologists "insist that biology must be so reduced to chemistry that biological laws and regularities could be deduced from what we shall learn about the chemistry of life processes." In fact, he thinks that constitutes an "unreasonable" form of reductionism.
One philospher, however, does stand out as being an extreme ontological reductionist: Jacques Loeb. Writing at the beginning of this century, Loeb believed that there was nothing to the universe save physics and chemistry. Loeb thought that even human will would soon be explained by physicochemical phenomena. All human (or animal) motivations are akin to a sunflower turning towards the sun--a physical imperative. In his most well-known monograph, The Mechanistic Conception of Life, Loeb says, "Since Pavlov and his pupils have succeeded in causing the secretion of saliva in the dog by means of optic and acoustic signals, it no longer seems strange to us that what the philospher terms an 'idea' is a process which can cause chemical changes in the body." To Loeb, ideas, desires, free will were all simply immediate manifestations of chemistry.
Paul Weiss responded to Loeb's ideas in his very first paper in 1925. He examined a butterfly that always moved its head away from the light. Loeb would say this was a perfect example of a physical imperative manifesting itself in a living organism's behaviour, akin to plants that move towards light. But Weiss found this too simplistic--after all, the butterflies did not reorient themselves in a prescribed or predictable way as does something indisputably mechanistic like billiard balls after a collision. Weiss did not reject the idea that the butterfly was reacting to physicochemical phenomena, he simply didn't believe it was the ultimate cause.
No matter whether or not one will succeed in an ultimate reduction of biological concepts to chemical or physical ones, the attempt to do so will always have to start out with the basic elements of biology and will thus be a reduction in toto, destined not to replace laws of the more complex field, but to coexist with them.
One must remember, claimed Weiss that the organism was a "unitary whole." Being an organism gave rise to certain properties that were unique to biology. We see in Weiss's work another version of emergentism, since he sees properties that emerge from the whole that are not there in the parts: "In the cell, certain definite rules of order apply to the dynamics of the whole system, in the present case refleted in the orderliness of the overall architectural design, which cannot be explained in terms of any underlying orderliness of the constituents."
Ernst Mayr points out that in the 1960s and 1970s the reductionist debate was mired in ambiguous language. There were three broad types of reduction being tossed around without much clarification or distinction: constitutive reduction, explanatory reduction, and theory reduction. Constitutive reduction is to describe a set of phenomena using the constituents of which they are composed. Theory reduction assumes that there are hierarchies of sciences and that the theories of the higher levels (i.e. biology) are simply special cases of the theories of the lower levels (i.e. chemistry)--in the same way that Keppler's laws of astronomical motion are now seen to be simply a sepcial case of Newton's laws of gravity. Philosophers who've worked with this kind of reduction rely heavily on symbolic logic and mathematics to relate a theory from one discipline to the theories of others. Last is explanatory reduction, which demands that all the phenomena of a higher level be explained by lower levels all the way down to the very lowest level. The anti-reductionist viewpoint here claims that at the higher levels new properties emerge that simply cannot be explained by the inherent properites of phenomena in the lower levels.
Explanatory reduction, with it's opposite emergentism, has been they type of reduction I've concentrated on so far. Constitutive reduction was also described earlier as having been debated in the last century. Today, however, it is embraced almost universally by the modern biologist. Organic processes clearly rely on physicochemical ones. Divide a cell up into continually smaller parts and you will eventually get to a quark, without ever violating any laws of physics or chemistry. Nor do modern biologists mistrust microscopes, chemical analysis, or spectrometry a la Bichat. Physical and experimental techniques are an integral part of modern biology. But this does not close the argument on the other two types of reduction.
Theory reduction was largely championed by Ernst Nagel. A philosopher whom Schaffner describes as being a "weak" ontological reductionist. Nagel set forth a methodical model for how one science could be reduced to another one. The Nagel Model, as it is called, takes the basic terms of one theory and relates them to the basic terms of another. Nagel set down two conditions for doing this. First is connectibility, in which "assumptions of some kind must be introduced which postulate suitable relations between whatever is signified by "A," a term appearing in the reduced science but not in the reducing science and the traits represented by theoretical terms already present in the primary or reducing science." Second is derivability, in which "with the help of these additional ssumptions, all the laws of the secondary [reduced] science, including those containing the term "A," must be logically derivable from the theoretical premises and their associated coordinating definitions in the primary discipline."
J.H. Woodger is known for making use of methods such as these to axiomatize biology. Just like the heralded methods of physics, he started with axioms and wrote out elaborate calculations "proving" biological laws. Few--if any--people followed up on Woodger's work and it is remembered today more for its laborious calculations than for its insights. Mary Williams also produced a mathematical model of evolution--starting from first principles and rigorously reconstructing Darwin's laws.
The previous two examples aside, Nagel's attempts at producing a comprehensive model for theory reduction did not meet with great enthusiasm. P.K. Feyerabend criticized Nagel, because he didn't believe that the conditions of connectability were realized in practice. In fact, in certain examples reduced theories were incommensurable with the reducing theory. Popper and Kuhn also found the requirements of connectability and derivability not well-defined, or not usable in practice. Kenneth Schaffner modified Nagel's model in an attempt to account for this issue. Schaffner named his new model the "general reduction paradigm." This most general (according to Schaffner) of reduction models incorporates the possibility that in reducing a science some theories may have to be replaced altogether, not just modified with a new description from the reducing science.
According to Mayr, in the 1960s Schaffner and Michael Ruse were examples in a pack of uncompromising reductionists, but that the number of strict reductionists has dwindled substantially since then. Schaffner has certainly softened on his position somewhat, if only in allowing more and more for replacement as opposed to mere reduction in his model. Let's bring up Ruse briefly before discussing the modern climate.
In his 1977 essay "Is Biology Different from Physics," Ruse brings up two examples that are often used to distinguish the two: complexity and teleology. He begins by acknowledging the vast complexity of biology,
Hence, in biology, so the argument goes, we have to settle for rather different kinds of understanding and explanation--more descriptive, more tuned to the particular, more ready to accommodate to the complex. And, as is well-known, there has been a proliferation of suggested models of biological understanding, models which do not demand full-blooded universal laws or tight logical connections between premises and conclusions. . . But surely there are some parts of biology where once can find laws, laws that are solid enough to bind into theories?
Ruse goes on to describe population genetics in a way that is consistent with statistical descriptions in physics. To address teleology he says that biology clearly has a teleological element not present in physics--if only because of the nature of biological adaptation through time. But the concept of adaptation is key--it does not pressupose an "echedemia" or even any emergent properties of living organisms. Ruse states that biologists do not mean to rely on the concept of a "final cause" when they propose function-based descriptions of organic characteristics. Biology he acknowledges, is more loosely organized than physics and comes with an irreducible teleological element, but that biologists "want to explain using laws in a hypothetico-deductive manner, and they have at least some success."
Ruse may still be considered a reductionist, but he accepts that there are some fundamental differences between biology and physics, and this acknowledgement seems to be a current trend. The problem has become less whether biology "reduces" to physics or chemistry, but whether or not it is an autonomous science, as Mayr puts it. The very concept of "reduction" places a hierarchy on the sciences, built up from the tacit assumption since the Scientific Revolution that physics and a glorified, perhaps innacurate, version of the scientific search for absolute truths and universal laws, is the pinnacle of science, the best description of our universe.
Mayr pronounces the attempt to reduce biology to physics a failure. Scattered through much of his writing and summarized in "Is Biology an Autonomous Science" he notes several fundamental ways in which biology differs from the physical sciences. Sheer complexity for one:
The complexity of living systems exists at every hierarchical level, from the nucleus, to the cell, to any organ system (kidney, liver, brain), to the individual, to the species, the ecosystem, the society. The hierarchical structure within an individual organism arises form the fact that the entitites at one level are compounded into new entitites at the next heigher level--cells into tissues, tissues into organs, and organs into functional systems. . . Systems at each hierarchical level have two properties. They act as wholes. . . and their characteristics cannot be deduced (even in theory) form the most complete knowledge of the components, taken separately or in other comibations. In other owrds, when such a system is assembled frm its components, new characteristics of the whole emerge that could not have been predicted from a knowledge of the constituents.
Additional important differences come from DNA, and the ability to store "historically acquired information," the comparative method of study in biology versus a strictly experimental one, the great individuality and uniqueness of various parts of the organic world leading to an inability to create "universal laws" in the way that physics does, and as a corrollary the inability to produce reasonable predictions as one can in the physical sciences. He concludes this essay saying,
The preceding list of biology's unique characteristics as a science explains why attempts to reduce biology and its theories to physics have been a failure. Does this mean that a unificationof science is impossible? Not in the least. All it means is that such a unification cannot be achieved by reducing biology to physics. Rather we have to search for a new foundation for such a unification. G.G. Simpson offers a solution: unite the sciences within the boundaries of biology. "The point is that all known material processes and explanatory principles apply to organisms, while only a limited number of them apply to nonliving systems. Biology, then is the science that stands at the center of all science, and it is here, in the field where all the principles of all the sciences are embodied, that science can truly become unified."
Whether or not it should be taken this far and biology should be set up at the center of all sciences, a growing number of philosophers have certainly begun to reject the historical hierarchy of the sciences accepted--usually unthinkingly--as a legacy from the Scientific Revolution.
One way in which this can be seen is in a new "type" of reduction that has received more and more attention of late: interfield reduction. In many ways this is not reduction in any kind of classical sense--for one thing, the concept of hierarchies within the sciences is not as dominant. Interfield--or interbranch--theories relate concepts from one field or branch to another. Maull and Darden point out that this is a different thing than the traditional form of reducing.
Theories were viewed as being of the same type, interpreted axiomatic systems, and the relations between theories also were though to take a single form, namely derivational reduction. After a derivational reduction had occurred, one theory had been 'eliminated,' at least in the sense that it had been explained as a deductive consequence of a more general theory. Reduction analyses were taken to provide an interpretation of the unity of science. . . and progress was identified with successful reductions.
Whereas setting up comparisons, and relations between various fields, does not necessitate completely replacing one theory with another. "An interfield theory, in explaining relations between fields, does not eliminate a theory or field or domain. The fields retain their separate identitites, even though new lines of research closely coordinate the fields after the establishment of the interfield theory."
Continuing in a similar vein--it has become clear that physics itself does not match the objective-experiments-leading-to-universal-laws stereotype that has been attributed to it. Quantum mechanics is a prime example of a statistical theory--no better and no worse than the non-statistical theories in physics--and consequently very similar to the statistical theories found in biology (I.e. in population genetics).
In summary, there are a few things one can state with certainty about the various reduction claims that have been preached throughout the centuries. Classic vitalism--the belief in some kind of "vital fluid" or "life force"--is dead And a fundamental belief that all things can be constitutively reduced to physics and chemistry is largely embraced by the scientific community. In other words, it is agreed that nothing happens in a living organism that somehow violates physicochemical laws. In the middle of this century attempts were made to impose rigorous mathematical techniques to biological theories and bring them into the more unambiguous realm of the physical sciences. While Schaffner continues to work with this kind of theory reduction it is less well embraced by others. Other debates in this century centered largely around the validity of emergentism--the concept that the complexity and uniqueness of biological organisms give rise to emergent properties not found in their mere parts. In the last decade or so, the discussions have not been couched in the language of emergentism per se, but emphasize the fundamental differences between biology and physics. Few, if any, philosophers would deny that there is a difference between the sciences as they are studied and the numbers of people who say that biology can be made to match physics are dwindling. This has not stopped an attempt at unifying the sciences and finding the places where they overlap, can offer cross-disciplinary insights, etc. But the modern day language of trying to unify the sciences is a different thing than reducing biology to fit into a physics mold.
Bernard, Claude. Introduction to the Study of Experimental Medicine 1865. Trans. Henry Copley Green (New York: Dover, 1957)
Darden, Lindley and Nancy Maull. "Interfield Theories." In Philosophy of Science, 44 (1977) 43-64.
Dobzhansky, Theodosius. "Introductory Remarks." In Studies in the Philosophy of Biology: Reduction and Related Problems. Ed. Fransisco Jose Ayala and Theodosius Dobzhansky, (Berkeley and Los Angeles: The University of California Press, 1974)
Goodfield, Jane. "Changing Strategies: A Comparison of Reductionist Attitudes in Biological and Medical Research in the Nineteenth and Twentieth Centuries." In Studies in the Philosophy of Biology: Reduction and Related Problems. Ed. Fransisco Jose Ayala and Theodosius Dobzhansky (Berkeley and Los Angeles: The University of California Press, 1974) 65-86.
Loeb, Jacques. "The Significance of Tropisms for Psychology." In The Mechanistic Conception of Life 1912, Ed. Donald Fleming (Cambridge: The Belknap Press of Harvard University Press, 1964) 35-63.
Mayr, Ernst. The Growth of Biological Thought. (Cambridge: Harvard University Press, 1982)
Mayr, Ernst. Towards a New Philosophy of Biology: Observations of an Evolutionist, (Cambridge: The Belknap Press of Harvard University Press, 1988)
Montalenti, G. "From Aristotle to Democritus via Darwin: A Short Survey of a Long Historical and Logical Journey." In Studies in the Philosophy of Biology: Reduction and Related Problems. Ed. Fransisco Jose Ayala and Theodosius Dobzhansky. Berkeley and Los Angeles: The University of California Press, 1974.
Nagel, Ernest. The Structure of Science; Problems in the Logic of Scientific Explanation (New York: Harcourt, Brace & World, 1961)
Popper, K. R. "Scientific Reduction and the Essential Incompleteness of All Science." In Studies in the Philosophy of Biology: Reduction and Related Problems. Ed. Fransisco Jose Ayala and Theodosius Dobzhansky (Berkeley and Los Angeles: The University of California Press, 1974) 259-284.
Ruse, Michael. "Is Biology Different from Physics." In Logic Laws and Life:Some Philosophical Complications. Ed. Robert G. Colodny. Unversity of Pittsburgh Series in the Philosophy of Science, 6. (Pittsburgh: University of Pittsburgh Press, 1977).
Schaffner, Kenneth F. Discovery and Explanation in Biology and Medicine (Chicago: The University of Chicago Press, 1993)
Simpson, G.G. This View of Life. (New York: Harcourt, Brace and World, 1964)
Weiss, Paul. "Animal Behaviour as a System Reaction: The Orientation Towards Light and Gravity in the Resting Postures of Butterflies (Vanessa)" 1925. In General Systems: Yearbook of the Society for General Systems Research. Trans. Gudrun S. Johnson (1959)
Williams, M. B. "Deducing the Consequences of Evolution: A Mathematical Model." In Journal of Theoretical Biology, 29