Leaf Reading in Oahu

Natural History, Sept, 2000 by Robert H. Mohlenbrock

A Hawaiian mountain trail provides plant detectives with plenty of exercise.

The third largest of the 131 islands in the Hawaiian archipelago, Oahu boasts such famous locales as Honolulu, Waikiki Beach, Diamond Head, and Pearl Harbor. From the first Polynesian settlers to the latest real-estate developers, human beings have had a huge impact on the island's environment, stripping away indigenous vegetation and introducing ornamental and crop plants from across the sea. But steep slopes and high elevations still harbor tracts of montane rainforest where many native species abound.

Oahu consists of two nearly parallel volcanic mountain ranges that run northwest to southeast. The rugged Waianae Range, on the island's western side, is the older of the two and includes Oahu's highest peak, 4,040-foot Kaala. On the eastern side is the Koolau Range, whose spectacular fissured cliffs front the windward side of the island. The Koolau mountains capture the greater part of the moisture shed by the trade winds, and their slopes were once completely cloaked in forest. Here the rainforest still survives above 1,650 feet

This correspondence between the Linnaean hierarchy and life's evolutionary tree achieves its clearest expression in pictorial form. The illustration on page 18 shows a Linnaean ordering of box within box; for alternative expressions of this hierarchy, see the diagrams of sequential genealogical splitting, opposite. Here we have a successive carving of the kingdom of all animals into, first, chordates contrasted with all other animals; then, vertebrates contrasted with all invertebrates; mammals contrasted with all other vertebrates; the order Carnivora contrasted with all other mammals; the family Canidae contrasted with all other carnivores; the genus Canis contrasted with all other canids; and finally, dogs contrasted with all other members of the genus Canis. (I stated that binomial nomenclature expresses the first step of this hierarchical ordering--and thus presents a microcosm of the entire scheme--because the two parts of a species' name record the first act of embedding smaller units within more inclusive groups of relatives. The name Canis familiaris states that this particular smallest unit, the dog species, ranks as one member of the next most inclusive group, the genus Canis, which unites all other species [including the wolf, Canis lupus, and the coyote, Canis latrans] that originated from a common ancestor shared by no other species in any other group.)

Linnaeus thought that his chosen scheme of mapping biological relationships as smaller boxes within successively larger boxes, until all units nested within the most inclusive box of life itself, represented the best human device for expressing the eternal order that God had chosen when he populated the universe. I doubt that Linnaeus ever. explicitly said to himself (for I suspect that his mental mansion included no room for such a thought): "But if, quite to the contrary, life evolved by a process of ever expanding branching from a single ancestor over a long period of time, then the hierarchical order of the binomial system will capture the topology of organic relationships just as well, because the logic of my system translates pictorially into a tree with a single trunk at the base, which subsequently divides into branches that never coalesce thereafter. I will therefore hedge and win in either case. For my chosen topology might represent either God's permanent order, preconceived from the first, or the happenstance of historical change and development on an evolutionary tree growing from a single starting point under the constraint of unbroken continuity (although branches may die and fall from the tree as lineages become extinct) and continuous bifurcation without subsequent joining of lineages."

I emphasize this property of irrevocable branching without subsequent amalgamation because the Linnaean logic of placing small boxes into larger boxes--which just happens to conform to the historical reality of Darwin's system--establishes just such a map of organic relationships as its primary and inevitable consequence. One can't, after all, either in Linnaean logic or in the real world, cram big boxes into smaller boxes. Therefore, for example, two species in the same genus can't reside in different families, and two orders in the same class can't be placed in different phyla. If lions and tigers rank as two species in the same genus (Panthera), they cannot then be allocated to different families of higher rank (lions to the Felidae and tigers to the Canidae, for example), for the two larger family boxes would then have to fit within the smaller box of the genus Panthera, and both the rules of Linnaean logic and the requirements of Darwinian evolutionary history would be fractured. I can be a monkey's uncle or a horse's ass only in a metaphorical sense, for my species fits into the small box of the genus Homo, which must nest within the larger box of the family Hominidae, and one member of my species can't opt out of our box to join the Cercopithecidae or the Equidae, thus splitting a coherent lower group into two higher groups. So just watch what you call me, you miserable skunk!