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

Discover, Feb, 1986 by Stephen Jay Gould

We revel in our persistent failure to resolve certain key arguments, because all the fun is in the fighting. Whatever shall we do if Lite's moguls ever resolve the ''tastes great-less filling'' controversy, thereby reconverting the field of American TV advertising to its former unmitigated wasteland? Thus, in a perverse sort of way, we actually regret the solution of some old scientific puzzles. Many people reacted with just this tinge of sadness to the recent announcement (Nature, Sept. 12-18) that pandas really are bears after all, not raccoons. The proof involved an array of independent techniques, all using the latest methods of molecular biology. Genes don't lie; the issue is closed.

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Somehow, I couldn't share this pleasure tinged with disappointment. I appreciated the Nature study for its decisive elegance, but it told me nothing I didn't already know. I have never doubted that giant pandas are modified bears. D. Dwight Davis proved this link, and debunked the alternativetie to raccoons, in our century's greatest work of comparative anatomy (The Giant Panda: a morphological study of evolutionary mechanisms). I read Davis's monograph when it first appeared during my initial year as a graduate student. He convinced me then, and his arguments remain as conclusive today. Most of my colleagues in the ''classical'' subjects of systematics and morphology hold Davis's work in equally high regard and do not doubt his principal conclusion.

The evidence of molecules has prevailed in public approbation, where earlier data of bones and muscles, equally persuasive in this case, did not. In asking why two equally impressive proofs had such different receptions, we must address some important and troubling questions about the nature of science and the styles of its translation from technical literature to public consciousness.

When Pere Armand David, the great French explorer-priest, acquired the Western world's first giant panda in 1869, he never doubted its evident affinity with bears. He even placed his specimen within the bear genus Ursus, christening it as a new species, Ursus melanoleucus. Although later continental naturalists considered the panda sufficiently distinct to merit its own genus (Ailuropoda), few ever doubted the basic affinity with bears--a tradition that has prevailed ever since among non-English-speaking naturalists.

In England, however, St. George Mivart identified the giant panda as an aberrant raccoon. (Mivart was a fine anatomist, known best for a critique of natural selection that Darwin himself took more seriously than any other challenge.) Mivart's opinion prevailed in English and American circles until Davis published his monograph--an interesting example of parochialism in science and the development of theories along national lines.

The great bear-raccoon debate would never have arisen if the deck of related carnivores hadn't contained a prominent joker--the so-called lesser panda, Ailurus fulgens. The giant panda looks so much like a bear that its sole existence would never have provoked such squabbling. But many naturalists insisted that the giant panda must be a genealogical sister to the much smaller lesser panda. And the lesser panda does, indeed, look very much like a raccoon. Thus, if the giant and lesser pandas form a coherent group, and if the lesser panda has affinities with raccoons, then we're forced to deny the commonsense link of giant panda to bear and assert the counter intuitive tie with raccoons.

Davis's assortment of this mixed deck was simple, and spot on (as the genetic data now affirm). He persuaded himself, first of all, that giant pandas could only be modified bears. His analysis (summarized below) involved an incredibly detailed 300-page scrutiny of every bump, bone, nerve, and blood vessel, accompanied by meticulous description, incisive analysis, and some of the most beautifully detailed (and colored) anatomical drawings ever published (most by Ms. H. E. Givans, who maintains a lively interest in natural history and has greatly enjoyed Davis's vindication; Davis himself died of lung cancer in 1965 at age 56).

Davis concluded, ''Every morphological feature examined indicates that the giant panda is nothing more than a highly specialized bear.'' He then recognized the simi- larities of giant and lesser panda as confusing results of independent evolution for common function, not as signs of genealogical relationship; they are, he proclaimed, ''convergences resulting from similar functional requirements; they are not similarities resulting from common ancestry.'' He regarded the taxonomic position of the lesser panda as ambiguous, but allied this species with raccoons: ''Its morphology resembles that of the Procyonidae [raccoons] more closely than that of any other family.'' In short, giant pandas are bears, lesser pandas may be raccoons, and the two pandas aren't close genealogical relatives.

The new genetic data include four independent tests (reported byStephen J. O'Brien, William G. Nash, David E. Wildt, Mitchell E. Bush, and Raoul E. Benveniste), each yielding the same an- swer--and each affirming Davis's conclusions. O'Brien and his colleagues began with DNA-DNA hybridization, an elegantly simple technique that combines all the single-copy DNA of two species by linking one strand of the double helix of species one with the complementary strand of species two. The more tightly the two strands bind, the more similarity in total genetic composition, and the closer the genealogical relationship. The second technique works from the opposite direction--detailed similarities of specific genes, rather than overall binding of the entire genetic program. For 50 genes O'Brien and his colleagues derived the same evolutionary tree that DNA-DNA hybridization had established. (This analysis didn't proceed by tedious and expensive sequencing of DNA bases, but indirectly by studying electrical properties of the proteins coded by these genes.) The third technique exploits the uncanny ability of vertebrate immune systems to rec- ognize (and reject) foreign tissue; degree of immune reactivity should measure evolutionary dif- ference--because proteins of closely related forms should be better accepted as ''self,'' those of more distant species decisively rejected. The immunological tree of the pandas, constructed about ten years ago by Vincent Sarich and others, matches exactly the hybridization and gene-distance schemes determined by O'Brien and his colleagues.

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

Discover, Feb, 1986 by Stephen Jay Gould

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