Compare it to paint samples at the hardware, to see the problem.
Over th past 150 years or so, paleontologists have found many representatives of the phyla that were well-known in Darwin’s time (by analogy, the equivalent of the three primary colors) and a few completely new forms altogether (by analogy, some other distinct colors such as green and orange, perhaps). And, of course, within these phyla, there is a great deal of variety. Nevertheless, the analogy hlds at least insofar as the differences in form between any member of one phylum and any member of another phylum are vast, and paleontologists have utterly failed to find forms that would fill these yawning chasms in what biotechnologists call “morphological space.” In other words, thy have failed to find the paleolontogical equivalent of the numerous finely graded ntermediate colors (Oedleton blue, dusty rose, gun barrel gray, magenta, etc.) That interior designers covet. Instead, extensive sampling of the fossil record has confirmed a strikingly discontinuous pattern in which representatives of the major phyla stand in stark isolation from members of other phyla, without intermediate forms filling the intervening morphological space. (p. 70)