Quoted from the author's "Introduction."
"The outstanding difficulty in this coveted unification of the contents of the universe is the nature of mind. The latest discoveries of the physicist have provided an ample base for the unification of all material things. Formidable difficulties remain in the task of reconstructing the whole process of development, but hardly any competent authority now has any misgiving about the ultimate unification. The dominating question is whether we can bring mind into this unity, and the present essay is concerned entirely with that issue. It does not
purport to be a contribution to psychology, since psychology disavows interest in such an issue. There have, however, always been two main theories of mind underlying psychological discussions: a theory that mind is an unique reality, unalterably distinct and remote in nature from the reality which we call matter, and a theory that mind is not a separate reality, but a different aspect of the same reality."
"The issue of this work is, therefore, quite distinct, not only from that of modern psychological treatises but also from that of the work of Romanes, Lloyd Morgan, and Hobhouse, which will at once occur to the reader. To their researches the writer has frequently to acknowledge his indebtedness, while frequently dissenting from their conclusions and interpretations, but they are mainly concerned to determine the precise degree and form of mind we may detect in the higher insects, birds, and non-human mammals. For my purpose this inquiry is subsidiary to a larger one, and I have given more
attention to the earlier cosmic phase in which mind was slowly emerging, and to the final passage from the non-human to the highest human level of culture. I have had, therefore, to neglect much that was relevant from their different point of view, and to include much that they neglected, or has been discovered more recently. My aim is, in short, to bring together whatever facts may be found to bear on the subject in a dozen sciences — chiefly, physics,
organic chemistry, geology, paleontology, zoology, physiology, psychology, and anthropology — and enable the reader to see whether the great advances which have recently been made in these branches of science have brought us any nearer to a verdict than we were in the days when monists, dualists, and parallelists fought their historic battles."