Darwin's Dangerous Idea by Daniel C. Dennett Read Free Book Online

cosmological alternative that had barely eluded Hume. Once his great idea occurred to him, he saw that it would indeed have these truly revolutionary consequences, but at the outset he was not trying to explain the meaning of life, or even its origin. His aim was slightly more modest: he wanted to explain the origin of species.
    In his day, naturalists had amassed mountains of tantalizing facts about living things and had succeeded in systematizing these facts along several dimensions. Two great sources of wonder emerged from this work (Mayr 1982). First, there were all the discoveries about the adaptations of organisms that had enthralled Hume's Cleanthes: "All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them"
    (Pt. II). Second, there was the prolific diversity of living things—literally millions of different kinds of plants and animals. Why were there so many?
    This diversity of design of organisms was as striking, in some regards, as their excellence of design, and even more striking were the patterns discernible within that diversity. Thousands of gradations and variations between organisms could be observed, but there were also huge gaps between them. There were birds and mammals that swam like fish, but none with gills; there were dogs of many sizes and shapes, but no dogcats or dogcows or feathered dogs. The patterns called out for classification, and by Darwin's time the work of the great taxonomists (who began by adopting and correcting Aristotle's ancient classifications) had created a detailed hierarchy of two kingdoms (plants and animals), divided into phyla, which divided into classes, which divided into orders, which divided into families, which divided into genera (the plural of "genus"), which divided into species.

    36 AN IDEA IS BORN
    What Is So Special About Species? 37

    Species could also be subdivided, of course, into subspecies or varieties—
    abstracting away from the grubby accidental properties of things to find their cocker spaniels and basset hounds are different varieties of a single species-, secret mathematical essences. It makes no difference what color or shape a dogs, or Canis familiaris.
    thing is when it comes to the thing's obeying Newton's inverse-square law of How many different kinds of organisms were there? Since no two organ-gravitational attraction. All that matters is its mass. Similarly, alchemy had isms are exactly alike—not even identical twins—there were as many dif-been succeeded by chemistry once chemists settled on their fundamental ferent kinds of organisms as there were organisms, but it seemed obvious that creed: There were a finite number of basic, immutable elements, such as the differences could be graded, sorted into minor and major, or accidental carbon, oxygen, hydrogen, and iron. These might be mixed and united in and essential. Thus Aristotle had taught, and this was one bit of philosophy endless combinations over time, but the fundamental building blocks were that had permeated the thinking of just about everybody, from cardinals to identifiable by their changeless essential properties.
    chemists to costermongers. All things—not just living things— had two kinds The doctrine of essences looked like a powerful organizer of the world's of properties: essential properties, without which they wouldn't be the phenomena in many areas, but was it true of every classification scheme one particular kind of thing they were, and accidental properties, which were free could devise? Were there essential differences between hills and mountains, to vary within the kind. A lump of gold could change shape ad lib and still be snow and sleet, mansions and palaces, violins and violas? John Locke and others had developed elaborate doctrines distinguishing real essences from gold; what made it gold were its essential properties, not its accidents. With