The following was written in partial fulfillment of the requirements of Dr. Greg Welty's Philosophy: Science and Religion class at Southeastern Baptist Theological Seminary.
The following was prepared as a one-page, single-spaced short response to a question from the readings for this class.
The natural sciences all claim to use the same basic model of knowledge, and claim to aim for the same kind of explanatory power: the law. However, clearly the kinds of laws which have such force in chemistry and especially physics are at least much less common in the other sciences; they may be entirely absent. Biology serves as a prime example of an unquestionably “hard” science in which laws are much harder to come by. Whereas physics includes both descriptive laws (PV = nRT) and explanatory laws (general relativity), biology seems entirely limited to the former. That is, there are e.g. laws describing how populations behave in an ecosystem, but there are no systematizing principles which are thought to offer the same degree of broad explanatory and predictive power as, say, the Standard Model of quantum mechanics. The closest example is a broadly Darwinian model of evolution, but even leaving aside questions about the accuracy of the model, it differs substantially from physical or chemical laws. It offers far less in the way of precise predictions, for one. For another, althought it serves as an explanation, the kind of explanation it offers is distinct in that it does not seem to have the kind of (nomic) necessity possessed by physical laws: even if Darwinian evolution is the means by which life arose on the planet, it by no means requires that life arose as it did; Certainly it is possible that life could have taken other forms even under the same selective pressures, given some other mutation—or have failed to succeed at all.
Biological systems (and yet-higher-level systems like ecologists or economies) demonstrate phenomena that supervene on the underlying physical realities. Unlike physics or chemistry, these phenomena seem, perhaps permanently, resistant to reductive and unifying explanations. This is precisely because of their lack of nomic or causal necessity: counterfactuals are easy to imagine in biology; much less economics. In the most abstract sciences—behavioral psychology, sociology, and economics, for example–it seems that human agency plays a major part in the actual outcomes in the world. Physicalist/materialist claims notwithstanding, it seems quite unlikely that such agency can be reduced to the results of chemical and electrical activity in the brain.1 Even at the level of microbes, however, the so-called “emergent behavior” of biological systems is not reducible to mere physical properties as is the case in physics and chemistry.
Again, counterfactuals play one significant part in this: biological systems could be other than what they are. But another significant factor is the purposive nature of organisms. Even the simplest living things2 have a teleological bent. Even if they were not designed, they themselves carry out certain patterns of directed behavior. They take in energy (eat). They reproduce. Even if this behavior is entirely deterministic, arising purely from the physical states of the organism, it remains irreducible to principles with broad explanatory force. “All living things consume from their environment for energy” is not an explanation; it is a description. “Objects’ motion as described by ‘gravity’ derives from the curvature of space-time’ is an explanation and not merely a description. Biological systems, still less conglomeration of such systems (especially those with minds!) both exist and behave in trivially counterfactuals ways, and therefore not only do not but probably cannot have the kind of nomic necessity present in non-emergent systems. If such a system does exist, it must consist of properties well outside our current sphere of knowledge.
That the physical state of the brain is closely related to and indeed affects mental state is unsurprising; that they would be the sole cause of mental states (and that there is no influence running the other direction) is a much stronger, and much less well-justified claim.↩
and, arguably, strange edge cases and hangers-on like viruses or prions↩