Fuzzy wuzzy was a bear. Andy Panda, too - giant panda related to bear, not raccoon

Davis recognized the key difference between morphology and molecules: morphology is an integrated system built by general rules of growth, not a set of independent items. If he could resolve his long list of differences as correlated consequences of a few changes in growth, then the closeness of pandas and bears would be affirmed. In other words (and in a brilliant stroke of argument), Davis proposed to use a feature of morphology that usually confounds homology--the potentially simple basis of apparent complexity--to understand the long list of bear-panda differences as multiple consequences of but a few underlying differences. The stunning success of this effort permitted Davis to see homology under the veil of an apparently impressive, but actually small, set of differences.

Davis correctly identified the key to this long list--a functional shift of panda ecology from ancestral carnivory to their present odd life (for members of the order Carnivora) as nearly exclusive consumers of bamboo. This shift entailed three major evolutionary changes--and Davis could reduce his list of bear-panda differences largely to the complex consequences of these few alterations. First, bamboo is much harder to chew and digest than meat. Pandas underwent a major change in dental and facial anatomy, increasing the size of grinding teeth, and greatly strengthen- ing the bones and musculature of face and jaws. Since morphology is an integrated system, not a set of independent structures, these changes ramified throughout the body. Selection upon a growth field that could strengthen bones and muscles in the face produced, for example, a set of correlated changes in shoulders and forelimbs--yielding the panda's characteristic ''unbalanced'' shape of overemphasized forequarters and ambling gait. If selective pressures for locomotory efficiency had been great, these non- adaptive side consequences of facial strengthening might have been eliminated, but pandas, in their bamboo forests, do not pursue active prey, need not escape enemies, and live surrounded by appropriate food. Thus, Davis concluded, selection pressures didn't arise to suppress the nonadaptive consequences of facial enlargement.

Second, pandas evolved a curious device to manipulate bamboo--a sixth digit (The Panda's Thumb of my recent book), built from the wrist's radial sesamoid bone. Davis proved that this change involved little more than simple enlargement of the sesamoid, but also entailed a set of conse- quences that gives a false impression of bear-panda differences if not properly reduced to a single change in growth pattern. Finally, pandas increased the parts of their brains that mediate these changes in feeding and food gathering.

In short, by understanding the long list of bear-panda differences as correlated consequences of only a few alterations in growth, Davis proved the deep similarity between bear and panda, and managed to recognize homology in the usually difficult data of classical morphology. He concluded that only half a dozen or so basic changes in growth might convert a bear to a panda--a result amply corroborated by genetic similarities only recently tabulated. The identification of homology requires a clear view of criteria, an attention to detail, and an understanding of proper evidence. Homology falls easily from DNA, but a master of morphology could find it just as well in the classical data of comparative anatomy. We end with some epitomizing doggerel, expressing a higher truth about pluralism in method, respect for proper canons of evidence, and correct taxonomic affinity.