Hot Dry Places - Tracks and Shadows: Field Biology as Art - page 74

camouflaged; they prey almost entirely on ants. Eric's studies also revealed that the
squat-bodied, spiny Australian moloch, kin to bearded dragons and other Old World
agamids, is comparably specialized: one stomach that he inventoried contained a mind-
boggling twenty-five hundred ants! Those features that independently evolved in horned
lizards and moloch he attributed to selection imposed by tiny, toxic, chitinous prey, so
low in quality that enormous numbers must be consumed, leading to huge stomachs that
preclude speedy escape from danger. On the ground, though, I couldn't help wonder-
ing about a Chilean tropidurine, Liolaemusmonticola, that eats only ants, hides among
rocks, and looks like nothing so much as western fence lizards in California chaparral.
If a narrow diet imposes such all-powerful selection, where were its horns?
Monitors were perplexing too. At the time, biologists explained their sharp teeth,
flexible skulls, and unusually high physical stamina as specializations for eating large
vertebrates, without, as it turned out, much in the way of supporting natural history
data. Yet when my grad student Jonathan Losos and I examined museum specimens of
varanids for comparison with long-nosed leopard lizards and monitor tegus, we were
taken aback as one after another good-sized individual contained beetles, snails, and
other diminutive prey. A two-pound, yard-long Bengal monitor proved typical of thirty
species we studied, having eaten some two dozen insects and a lizard—its heaviest item,
and the only vertebrate prey, weighing less than an ounce. A few varanids do specialize
on mammals, while at least one eats mainly fruit, but they're deep within a family tree
of generally large lizards that we proved consume mostly small items. 16
Conventional wisdom about monitors amounted to just the sort of “adaptive
storytelling” ridiculed in a 1979 paper by two Harvard biologists, 17 Stephen Jay Gould,
who had achieved fame for his masterful Ontogeny and Phylogeny 18 and monthly Nat-
ural History magazine essays, and Richard Lewontin, highly regarded as a molecu-
lar evolutionist and leftist intellectual. Together they'd vehemently opposed colleague
Ed Wilson's Sociobiology, 19 complaining that his enthusiasm for genetic determinism
and selectionist explanations of human behavior encouraged racist politics. Now they
made sweeping arguments that adaptation is difficult to prove and that the side ef-
fects of design requirements or, in humans, culture play more important roles. Sure,
they admitted, selection might account for moth wing colors, but not skull differences
between horses and lions, let alone anything involving our behavioral norms. The ensu-
ing squabbles were also prone to authoritarian rhetoric—Harvard's Ernst Mayr asserted
that convergent evolution provides ample evidence for ancestral selection 20 —but they
fostered a more widespread, healthy skepticism.
Henry Fitch might have smiled at Mayr's failure to link natural history more directly
with evolutionary history, given the elder biologist's earlier criticism of his gartersnake
dissertation, but Steve Gould's role in rehabilitating “adaptation” was far more ironic
and influential. However brilliant, here was an unabashed urbanite who scoffed at affec-
tion for warm and fuzzy creatures, 21 a polymath who studied fossil snails, downplayed
predation and other selective factors, and claimed that exotic organisms are superiorly
adapted—“astonishingly,” as mammalogist Tim Flannery noted, since invaders lack nat-
ural predators and thus “this argument takes no account of ecology.” 22 Nonetheless,
Steve's 1982 proposal with Elizabeth Vrba that preexisting traits are exapted for novel
uses supplied a pivotal insight. 23 As Losos and I soon demonstrated with monitors, evol-