The tree of life grew, its branches stretching toward complexity. Organisms developed systems, subsystems, and sub-subsystems, layered in ever-deepening regression. They used these systems to anticipate their future and to change it. When they looked within, some found that they had selves—constellations of memories, ideas, and purposes that emerged from the systems inside. They experienced being alive and had thoughts about that experience. They developed language and used it to know themselves; they began to ask how they had been made.

This, to a first approximation, is the secular story of our creation. It has no single author; it’s been written collaboratively by scientists over the past few centuries. If, however, it could be said to belong to any single person, that person might be Daniel Dennett, a seventy-four-year-old philosopher who teaches at Tufts. In the course of forty years, and more than a dozen books, Dennett has endeavored to explain how a soulless world could have given rise to a soulful one. His special focus is the creation of the human mind. Into his own he has crammed nearly every related discipline: evolutionary biology, neuroscience, psychology, linguistics, artificial intelligence. His newest book, “From Bacteria to Bach and Back,” tells us, “There is a winding path leading through a jungle of science and philosophy, from the initial bland assumption that we people are physical objects, obeying the laws of physics, to an understanding of our conscious minds.”

Dennett has walked that path before. In “Consciousness Explained,” a 1991 best-seller, he described consciousness as something like the product of multiple, layered computer programs running on the hardware of the brain. Many readers felt that he had shown how the brain creates the soul. Others thought that he’d missed the point entirely. To them, the book was like a treatise on music that focussed exclusively on the physics of musical instruments. It left untouched the question of how a three-pound lump of neurons could come to possess a point of view, interiority, selfhood, consciousness—qualities that the rest of the material world lacks. These skeptics derided the book as “Consciousness Explained Away.” Nowadays, philosophers are divided into two camps. The physicalists believe, with Dennett, that science can explain consciousness in purely material terms. The dualists believe that science can uncover only half of the picture: it can’t explain what Nabokov called “the marvel of consciousness—that sudden window swinging open on a sunlit landscape amidst the night of non-being.”

Late last year, Dennett found himself among such skeptics at the Edgewater Hotel, in Seattle, where the Canadian Institute for Advanced Research had convened a meeting about animal consciousness. The Edgewater was once a rock-and-roll hangout—in the late sixties and seventies, members of Led Zeppelin were notorious for their escapades there—but it’s now plush and sedate, with overstuffed armchairs and roaring fireplaces. In a fourth-floor meeting room with views of Mt. Rainier, dozens of researchers shared speculative work on honeybee brains, mouse minds, octopus intelligence, avian cognition, and the mental faculties of monkeys and human children.