This is the problem of reductionism, how to explain complex systems in terms of their numerous component parts. The language of cells is molecules, so it is rational to try and explain the behaviour of cells in terms of the behaviour of the billions of molecules that make up the cell. But do I really want to explain the behaviour of the molecules in terms of their chemistry, and moving to a yet lower level, in terms of quantum mechanics? Most of us are content to understand how DNA codes for proteins without the slightest attention to the chemistry involved. As for quantum physics, forget it. It is a matter of taste what scientists will accept as a satisfactory explanation and the molecular understanding of cells has been startlingly successful.
My confidence in reductionism, which I claim is at the heart of all good science, was however a bit undermined when I learnt that thousands of our genes code for different, but related, molecules on the cell surface that receive signals from other cells, and further thousands are involved in getting the messages to the cells' DNA. What are they all doing and how will we ever find out? If God is in the details we may be in trouble.
The heart provides another nice example of how new properties emerge when many units are put together. Great advances have been made in understanding the properties of individual heart cells and particularly the processes that generate the rhythm. Denis Noble of Oxford University has emphasised that this understanding does not lead naturally or easily to understanding how the cells co-operate to produce a functioning heart. Abnormalities in the rhythm of the heart that can lead to heart attacks can only be understood at the level of the whole heart. He has shown that it is possible to provide this integration by modelling the behaviour of the heart in terms of its individual cells on a computer and the results are very encouraging. Quite new and unexpected behaviours emerge.
How much more so is the case of the brain and behaviour in relation to nerve cells. Our inner ear, for example, is made up of a million finely made moving parts. There is no reason to doubt that our minds behave in the way that they do because of the behaviour of the cells in our brains. But, as yet, the action of groups of nerve cells cannot explain behaviour in the way that molecules explain cells. Just think of language where there is to date no understandable connection to nerve impulses. Nor is it clear that there will ever be. It could be that while we may in the future be able to simulate brain functions on computer we may have little understanding of what is going on. But, be patient. We do not know what new ideas, techniques, and discoveries will give totally new insights. Even consciousness may not be beyond reach.
Changes in the number of component parts in a system can undoubtedly give rise to quite new properties. As Hemingway observed, the rich are different - they have more money.