This book is an evolutionary history of life on earth. Its focus is not the evolution of the structural/functional adaptations found in any biology textbook, though these are necessarily discussed in a general way. It's primarily concerned with consciousness, with what the organism experiences. Just how far back into evolutionary history consciousness extends, of course, is a highly controversial issue, and one which we will probably never resolve with certainty. We know we are conscious, and most people would probably extend consciousness to other mammals, but when it comes to lower vertebrates, let alone invertebrates, there is no consensus. This book takes a "what if" approach. What if all forms of existence were conscious to some extent, a view known as panpsychism or panexperientialism? Based on those aspects of their function and behavior that we can actually observe and measure, what can we say about what this consciousness is like? The resulting story is one in which consciousness becomes increasingly more complex over evolutionary history, yet is based on facts of animal behavior that any reader, regardless of personal views on consciousness, can accept. In order to simply a vast amount of scientific literature, the book focuses on two general properties of consciousness and its behavioral manifestations: the experience of an outer world embedded in space and time; and that of an inner self that is defined by its relationship to other organisms. Two key claims made are that 1) dimensions of externally-perceived space and time have emerged more or less one at a time over the course of evolutionary history; and 2) the number of spatial/temporal dimensions experienced by any organism in the outer world is closely related to experienced inner dimensions in its relationships with other organisms. For example, the simplest invertebrate organisms experience one dimension of space, in the form of intensity discriminations made of simple stimuli such as light, touch and chemical substances. Closely correlated with this one-dimensional experience of the outer world is the ability to make simple self-other discriminations, in which the organism in effect distinguishes itself one-dimensionally from the outer world. Somewhat more evolved invertebrates, such as arthropods, experience two dimensions of space, their perception being largely limited to shapes, contrasts, and surfaces. They can also distinguish between two dimensions in their relationships with other organisms, as exhibited in the ability to discriminate such classes of other as male vs. female and kin vs. non-kin. The most highly evolved invertebrates, as well as all vertebrates, experience additional dimensions of space and/or time and make still finer discriminations among other organisms. The evolutionary story is not confined to organisms, however. The book argues that the same kind of dimensional relationships exist on lower levels of existence. Thus there are atoms that recognize and interact with other atoms in various degrees of dimensions, and there are cells that recognize and interact with other cells in different numbers of dimensions. Again, the minimal claim being made is that the function and behavior of these lifeforms can be understood in terms of dimensions, while leaving it up to individual readers to decide whether this could reflect a similar dimensionality of consciousness. Review by Kirkus Discoveries A lucid, thought-provoking and wide-ranging metaphysical treatise by novelist, scientific researcher and Stanford Ph.D. Smith. Heralded as "the first complete history of consciousness ever written," The Dimensions of Experience covers an astonishin