I should probably never have undertaken to write a work of this kind had it not been for the honour conferred upon me by the University of St. Andrews in appointing me Gifford Lecturer for the years 1969–71. The will of Lord Gifford instructed the Lecturers to deal with natural religion and “to treat their subject as a strictly natural science, the greatest of all possible sciences…” It is also specifically stated that the Lecturers shall be under no restraint whatever in the treatment of their themes. Faced with an opportunity of this kind one naturally gives careful thought to the topic and scope of one's lectures, and I chose my title, bearing in mind several related reasons.

Firstly our views on human nature are fundamental to the whole development, indeed the whole future, of society in this epoch of an overpopulation catastrophe. It is only too clear, and not in the least surprising, that human life appears to be less generally valued than at any time in the past hundred years or more. There are a number of possible reasons for this, but two of them are I think particularly clear. Firstly there are already too many people in the world so that, however humane and benevolent we may be, one cannot help feeling a twinge of satisfaction (if the disaster is not too near us, personally) at anything which reduces the population a little, however trivially. Secondly the widespread, often subconscious, acceptance of the outdated view of science, that man is simply the product of vast machine-like evolutionary forces, can easily lead to a hopeless loss of faith in the value of human beings and a consequent sense of the futility and purposelessness of our existence. It accordingly seemed to me that the position of Man in the animal kingdom, his evolutionary relationships to the rest of the living world, as far as these can be reasonably presumed, is one of the most important and significant topics to which a biologist can address himself. And granting this, it is essential that people should be shown both the characteristics in which the animal world approaches, and in some cases greatly exceeds, mankind in achievement and those characteristics of man that cause us sometimes to feel that we are brutes and at other times that we are gods.

I felt convinced that it would be futile to talk in general terms about the similarities and differences between animal and human nature because, in spite of many popular works on both, the field is vast and complex; moreover knowledge is accumulating at a formidable rate. This means that the particular facts that are relative to such a discussion must be selected and marshalled with the immediate ends of the discussion constantly in mind.

A matter of prime importance emerged as soon as I began to think seriously about lecturing and writing on such a topic—namely this: it would be useless to launch into a consideration of man, how far he is unique and how far he is just an exceptional animal, without first examining the question of the origin of the lower animals and indeed of life itself; for if the lowest forms of life are fully explicable in terms of non-living existence—that is to say if all the features of any living organism can be fully described in terms of chemistry and physics—then it would be that much more probable that Man himself could be “explained” in purely animal terms, and thus, as a further remove, in terms of the world of physics and chemistry. So the problem of the nature and origin of life at once became basic to the whole enquiry.

As will be seen, the answer becomes surprisingly definite. The general trend of the work of philosophers of science in the last half century has been increasingly to make clear that in spite of the enormous progress of science in explaining the complex in terms of the simple, and special cases as instances of general laws, there are big and seemingly unbridgeable discontinuities in the account of the world as we range from the supposed “primordial gases” and particles to this stupendously complex and awesomely great universe which we now realise we inhabit.

Thus it now seems clear that however perfect our knowledge of the details of any supposed “primordial nebula” might have been, and however thorough our understanding of the particles of which such a nebula could have been constituted, it would still have been logically impossible to have foretold the development of the world of heavy atoms such as carbon and iron on which life as we know it must depend. That is to say the world which the chemist studies can, it seems, never be fully explained and interpreted in terms of physics. Rather there seems to be a real discontinuity—a real unforeseeable emergence of something new. Similarly the marvellous epoch of discoveries of the genetic code through which we have recently lived seems, quite contrary to the popular belief, to make it far less comprehensible how life might have arisen from non-living than it was before. The possibilities of this having happened “by chance” are, so far as we can see, so infinitely improbable that science as such can hardly have an opinion to express. Life may have arisen many times in the history of the cosmos; it may on the other hand be absolutely unique and have arisen only once. Science has, as yet, no grounds for considering one alternative more probable than another. Similarly when we come to the other great frontier of knowledge, the relation between the private world of personal consciousness and the world picture resulting from the application of the scientific methods of, for instance, physics, biochemistry, genetics and physiology, we are again confronted with a seemingly unbridgeable gap where something truly and completely new appears to have emerged over the horizon.

Now it is clear that the scientist must always try to interpret and explain the complex in terms of the simple, the “higher” in terms of the “lower”; for that—reductionism as it is called—is of the very nature, the basic technique, of the scientific enterprise. Indeed all of us working scientists regard this as our universally applicable conceptual tool. Yet we have compelling logical reasons for believing that science, from its very nature, can never yield a complete self-coherent picture of the world. There will always be a residue, something behind and beyond, which science is unable to grasp.

The Lectures from which the book arose were given to a stimulating and rewarding audience which included undergraduate and graduate students and staff from several different faculties—scientific, philosophical, and theological. With such an audience comprising such a range of age, interests, and approaches I naturally strove for eclecticism, and this has inevitably influenced the form and content of the book. It also meant that the treatment had often to be cursory, and many topics might certainly have profited by much fuller discussion than I have given them. However the book is already larger than I intended it to be and to have extended it still further would have involved a two-volume work at least and a much longer delay in publication. Where I have gone into fuller detail, e.g., Chapter 3, it is because I feel that while the non-specialist reader may be fairly well acquainted with, say, the recent developments in the study of monkeys and apes, he is likely to know far less about the astounding behavioural and sensory abilities of some of the “lower animals.” Yet the study of birds and fish and also of some of the invertebrates such as insects and sea anemones, and even humbler creatures, reveals facts which, in their way, are just as important as evidence for “animal nature.”

I have tried to give references to the more important general works for more detailed study, without overburdening the bibliography unduly. However, Chapter 3 is something of an exception in that it contains so much new factual material, as yet little available in works of general reference. So here I felt more detailed citations and explanations to be desirable.

W. H. THORPE

Cambridge, November 1972