Editor's comment

Patricia Smith Churchland is Chair of the Philosophy Dept. at UCSD. Her work relating recent brain studies with philosophy is extensive.

Reading on: Neuroscience, metaphysics and evolution

Churchland, Patricia Smith Brain-Wise: Studies in Neurophilosophy The MIT Press, Cambridge, MA 2002 [abridged – 1110 words]

The more we understand about brains, their evolutionary development, and how they learn about their world, the more plausible that the pragmatists are on the right track concerning the scope and limits of metaphysics. The explanation is quite simple: We reason and think with our brains, but our brains are as they are — hence our cognitive faculties are as they are — because our brains are the products of biological evolution. Our cognitive capacities have been shaped by evolutionary pressures and bear the stamp of our long evolutionary history.

If, as seems evident, the main business of nervous systems is to allow the organism to move so as to facilitate feeding, avoid predators, and in general survive long enough to reproduce, then an important job of cognition is to make predictions that guide decisions. The better the predictive capacities, the better, other things being equal, the organism’s chance for survival. In a population of organisms, those who are predictively adroit do better than those who are predictively clumsy, other things being equal.

When an organism survives long enough to reproduce, its offspring inherit its genes, and thus inherit the capacities whose structures are organizationally dependent on those genes. Occasionally an offspring has tiny changes in its genes, a mutation, that results in the organism being structurally somewhat different from its parents. Usually such mutations are disadvantageous. On rare occasions, however, a mutation will give the offspring a change in brain or body structure that, relative to the organism’s environment, ends up conferring a bit of an edge in the struggle to survive. If an organism with the advantageous mutation does survive and reproduce, its offspring will inherit the modified capacity. This is descent with modification.

For the pure metaphysical approach to the mind, the implications of descent with modification are troubling. For example, it implies that a fancy visual system will not emerge just for the sheer excellence of having fancy perception. Unless improvements in visual capacity make a net contribution to the organism’s overall capacity to survive, they will tend to vanish along with the organism. When an offspring happens to have a mutation in its genes that dictates a structural change in the nervous system that gives the organism a perceptual capacity that allows it to make better predictions than its competitors can make, then that organism is more likely to survive and pass its genes on to its offspring. Importantly, however, if the mutation comes at a cost to the organism — if, for example, there is a trade-off between speed of processing and sophistication of perceptual images — then a given mutation may carry a net loss, even though the higher degree of accuracy of perception is predictively useful when considered alone.

From the perspective of Darwinian evolution, therefore, any beyond-science metaphysics has to face a tough question: Would there have been evolutionary pressure for the emergence of a special faculty with a unique route to Absolute Metaphysical Truth? What could have been the nature of such pressure? Is there a plausible account consistent with natural selection that can explain how humans could come to have such a capacity? Relative to what is now known, it is doubtful that any such account is forthcoming, even if one can envisage what such a capacity would be like. Consequently, we do best to resign ourselves to the probability that there is no special faculty whose exercise yields the Absolute, Error-Free, Beyond-Science Truths of the Universe. All we can do, though it is certainly no small thing, is to learn what the best available science says, mindful that it may embody errors, both large and small, and then subject it to criticism, refinement, and extension via more of the same — experimenting, theorizing, and thinking things through.

Still, it may be urged that one’s feeling of having made progress in supra-scientific metaphysics should count for something, and the conviction that such progress has been made does indeed exist. More exactly, feelings of certainty may be cited as the benchmark for having discovered a Beyond-Science
Metaphysical Truth. For example, feelings of unshakable conviction or absolute certainty may accompany consideration of the hypothesis that the mind is a nonphysical substance. Descartes seems to have enjoyed such certainty and to have believed it warranted a specific conclusion.

Feelings of certainty, however, are no guarantee of truth. They can, of course, motivate testing a hypothesis for truth. They can motivate continuing a research project even in the face of scoffers. But feeling certain that a hypothesis is true is, sadly, all too consistent with falsity of the hypothesis. Everyone knows of occasions in his own life when certainty and falsity were happy bedfellows. Moreover, the historical record is painfully clear on this matter. At various times, people have been completely certain that the Earth did not move, that space is Euclidean, that atoms are indivisible, that insanity is caused by possession of demons, that they can see into the future, and that they can communicate with the dead. Yet all of these propositions are probably false. That falsity and conviction coexist should not surprise us. Certainty, after all, is but a cognitive-emotive state of the brain, one such state among many other cognitive-emotive states of the brain.

The pragmatic conception of metaphysics may seem a bit of a disappointment, for much the same reason that it may seem disappointing that our universe has is no such thing as Absolute Space or Lady Luck or Guardian Angels. Having to muck on as best one can seems a lot less romantic, perhaps, than being on a quest for supra scientific Metaphysical Truth. Nevertheless, in making progress, we abandon romantic notions when their wheels fall off.

What metaphysical questions still remain to be resolved? One sub field in physics where fundamental issues about the nature of reality remain very much alive is quantum mechanics. On the significance and interpretation of quantum mechanics, there is fruitful interaction between physics and the philosophy of physics.

There is a mind-body problem only if the mind is nonphysical and the body is physical. The nub of the problem is how the two substances can interact and have effects on one another if they share no properties whatever. How, for example, can mental decisions have an effect on neurons, or how can directly stimulating the cortex with an electrode result in feeling one’s leg being touched? On the other hand, if the mind is activity in the brain, then that particular problem, at least, does not exist. Other problems of exist, to be sure, but not the problem of the interaction between soul stuff and brain stuff.