All features in the natural world are organized in a hierarchy, which can be understood to be a successive ranking of subsets within sets. A familiar hierarchy, for example, is rank within

Dna Evolutionary Hierarchy
Figure 3.3. A tree of life. This particular one is a satire by Matt Groening. The image of evolution as a tree, however, is completely familiar. From the Big Book of Hell © Matt Groening. All Rights Reserved. Reprinted by permission of Pantheon Books, a division of Random House, Inc., NY.



'ISMs anima,

Vertebrates Puzzle

MAMMALS (vertebrates with fur)

VERTEBRATES (possess backbones)

MAMMALS (vertebrates with fur)

VERTEBRATES (possess backbones)


(bilaterally symmetric organisms)

Figure 3.4. The natural hierarchy illustrated as a wooden jigsaw puzzle. The different organisms represent the larger groups to which they belong. For example, the mouse, representing Mammalia, and the lizard, representing Reptilia, together fit within the puzzle to represent Vertebrata, itself a subset of bilaterally symmetrical organisms (Bilateria), which would include invertebrates such as a lobster or a mosquito. Bilateria and other groups constitute the group of organisms we call Animalia (animals).

the military. To choose a biological example, all creatures possessing fur1 are a subset of all animals possessing a backbone, which are in turn a subset of all living organisms (Figure 3.4); these features are distributed hierarchically. In fact, all features of living organisms are hierarchically distributed in nature, from the possession of DNA - which is almost ubiquitous - to highly restricted features such as the possession of a brain capable of producing a written record of culture.

Always, however, unmodified or slightly modified vestiges of the original plan remain, and these provide the keys to the fundamental hierarchical relationships that reveal who's related to whom.

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