I have, however, experienced a major transformation that I will try to explain. In the last edition I wrote that human sexuality was an enigma or a riddle. Since then this enigma has become endowed with even more significance for me. Scientific progress, while it may bring clear practical benefits, more often than not makes the human condition more rather than less difficult to understand. No doubt there are exceptions, but in my experience they have been few. One particularly telling example, which I will revisit at several points in this book, is brain imaging. We may use brain imaging to study what happens in the brain when we become sexually aroused, or to compare and contrast individuals with normal and low levels of sexual desire. What we find is a multiplicity of interactive brain functions that do not slot easily into our preconceived concepts of ‘sexual arousal’ or ‘sexual desire’. And why should they? The common assumption that we can work out, with our brains, how those brains work, is one aspect of the arrogance of human beings. There are many, beyond the field of brain science, who believe that it is only a matter of time before science gets everything worked out. This has not made me nihilistic about scientific research, far from it; the practical benefits of research continue to be considerable. But it has made me more humble, and in the process has intensified my sense of spirituality.

— Human Sexuality And Its Problems, 3rd ed. by John Bancroft