One of the major tasks remaining for biological science is to explain human consciousness. Human consciousness is our highest, most complex faculty, and is characterised by self-consciousness and free will. At present science is nowhere near explaining this complex phenomenon, and, it seems to me, it may never explain it in the terms in which the search for explanation is usually framed.
Science tells us that the physical universe is composed of fundamental particles (quarks, electrons, etc.) that are acted upon by fields of force (the strong and weak nuclear forces, the electromagnetic force, and gravity). The various particles aggregate together to form all the things we see in the macroscopic world - including ourselves.
Science is designed to investigate the natural world, which, in practice, mostly means the physical world. But many real things exist in the real world that have no physical manifestations, e.g. emotions, desires, ethics, credit, ambition, etc. In other words, nobody could hand you a lump of pride or a force-field of ambition in the same way as they could hand you a lump of sugar or give you an electric shock.
When science tries to explain these various "non-physical" things, it usually tries to find the underlying physical activity that "causes" these phenomena. This approach is entirely appropriate and productive when attempting to achieve an understanding of many phenomena. A classic example was the discovery that DNA is the "cause" of the transfer of hereditary information from one generation to the next. But this reductionist approach of looking for underlying physical causes in small sub-components of a whole is not the appropriate way to understand all phenomena.
The philosopher Mary Midgley explains this latter point very well in a chapter in the recent book From Brains to Consciousness (Ed. Stephen Rose, Penguin 1999). She uses money as an example. Money is a device used to value goods and services and is used to exchange for goods and services. In order to understand money you must look at why people want to trade. Any analysis of the physical nature of money will tell you nothing significant about the phenomenon of money. It is also equally unlikely that analysis of electrical activity in the brains of those who spend money would shed any light on money.
Again, consider a large shopping complex. It will contain many shops, elevators, restaurants, toilets, banks, creche, cinema (perhaps), telephones, etc, and, of course, many shoppers. How would your stereotypical Martian, who had never seen humans or such a shopping complex before, go about achieving an understanding of it?
First of all, the Martian would notice the great qualitative difference between the humans who move about purposefully and the static structure of the physical complex. A traditional scientific reductionist approach would separate the humans from the complex and reduce each to its simplest components. The shopping complex would reduce mainly to concrete and steel and the humans would reduce to living cells. This information would be useless in itself in explaining the shopping complex and I cannot see how it would indicate any useful start to any programme of further investigation that would eventually produce a correct answer. In order to understand the shopping complex, you must study it as a functioning whole.
In the above example it is of course true that the shopping complex is ultimately dependent on (and in that sense "caused" by) concrete, steel and cells, and while this knowledge might, in some tiny way, help the Martian's understanding, it would seem to be impossibly difficult to build up from this level to achieve an understanding of the whole.
So, why would such a complicated and unpromising approach ever be contemplated as the main avenue of approach to explaining complex phenomena such as the functioning of the human brain? I think the answer is that such an approach relies entirely on physical measurements, the only measurements many scientists feel comfortable with. Such an approach also models the science of physics whose approach is to simplify the natural world into as few fundamental particles and forces as possible.
Molecular biology is the branch of biology that has been most spectacularly successful in recent decades. It is the branch of biology that gave us DNA, the chemical nature of the gene, and genetic engineering. Molecular biology has very successfully used the physics model in order to pursue its goals. The great success of molecular biology has convinced many scientists that this approach can solve all biological problems.
But the worm at the heart of this approach is the underlying assumption that the only real explanation of anything is a physical explanation. Many scientists are comfortable only when dealing with physical entities and feel uncomfortable when asked to examine directly phenomena that have no obvious immediate physical body, e.g. emotions. The instinct is to look immediately at the physical structure of the "associated organ" and reduce it to its smallest sub-components. And so, many scientists would think of the brain in an analogous way to the liver and conclude that the complicated structure of the brain secretes thoughts just as the liver secretes bile. But it may well be as unprofitable to think about the brain exclusively in these terms as it would be to try to understand money by analysing the composition of metal coins and paper notes.
Finally, let me say that I am not arguing that some special vital force underlies the complex phenomenon of consciousness. My argument is that, as Midgley points out, we live in a big world of huge variety and that different approaches must be taken in order to understand different types of things. The approach taken by physicists is powerful, is appropriate to physics, and can produce useful results in biology. But this approach is not the Philosopher's Stone.
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.