the realm of physics and mechanism on the one hand with the realm of meaning and purpose on the other. From a Darwinian perspective the continuity between lifeless matter on the one hand and living things and all their activities and products on the other can be glimpsed in outline and explored in detail, not just the strivings of animals and the efficient designs of plants, but human meanings and purposes: art and science itself, and even morality. When we can see all of our artifacts as fruits on the tree of life, we have achieved a unification of perspective that permits us to gauge both the similarities and differences between a spider web and the World Wide Web, a beaver dam and the Hoover Dam, a nightingale’s nest and “Ode to a Nightingale.” Darwin’s unifying stroke was revolutionary not just in the breadth of its scope, but in the way it was achieved: in an important sense, it turned everything familiar upside down. The pre-Darwinian world was held together not by science but by tradition: all things in the universe, from the most exalted (“man”) to the most humble (the ant, the pebble, the raindrop) were the creations of a still more exalted thing, God, an omnipotent and omniscient intelligent creator—who bore a striking resemblance to the second-most exalted thing. Call this the trickle-down theory of creation. Darwin replaced it with the bubble-up theory of creation. One of Darwin’s 19th century critics put it vividly:

MacKenzie (1868)

This was indeed a “strange inversion of reasoning,” and the outrage and incredulity expressed by MacKenzie more than a century ago is still echoing through a discouragingly large proportion of the population in the 21st century. A page from a 20th century creationist pamphlet (Fig. 17.1) perfectly captures the “obviousness” of the intuition that Darwin’s theory overthrows.

When we turn to Darwin’s bubble-up theory of creation, we can conceive of all of the creative design work metaphorically as lifting in Design Space. It has to start with the simplest replicators, and gradually ratchet up, by wave after wave of natural selection, to multicellular life in all its forms. Is such a process really capable of having produced all of the wonders we observe in the biosphere? Skeptics ever since Darwin have tried to demonstrate that one marvel or another is simply unapproachable