Early twentieth-century scientists forgot Edward Cope’s neo-Lamarckian ideas, but they still faulted Darwin for not explaining “the origin of the fittest,” the source of the variation that he said natural selection needs to operate. Without such a source, evolutionary change of any kind would not occur, since organisms would simply remain the same from generation to generation. Many evolutionists became so obsessed with variation’s origin that they almost forgot about Darwin. It seemed possible that changes in the “germ plasm,” genetic mutation, might be the main force in evolution, with natural selection a secondary factor. Mutations might allow organisms to give birth to new forms without undergoing a lengthy, random process of “descent with modification,” as Darwin originally called evolution. They might produce “hopeful monsters,” offspring that differed radically from their parents in ways that luckily made them much more fit to survive and reproduce in their turn.
An early attempt to explain California desert evolution reflected this. In 1902, the Carnegie Institution of Washington, D.C., established a desert research laboratory in Tucson. Its first director was Daniel Trembly MacDougal, originally of the New York Botanical Garden. Desert biology might seem a stretch from that genteel setting, but MacDougal was a sportsman and socialite as well as a botanist. He divided his time between the Tucson lab, a Carmel, California, home (where he became an intimate friend of Mary Austin in her postdesert years), New York and Washington clubs, and field expeditions that included research in the Colorado Delta region. In the process, he acquired a wide if not necessarily deep acquaintance with biological issues concerning the desert’s past: “Desert conditions seem to have prevailed in . . . southwestern America since Cretaceous times. In the . . . Salton basin of California . . . the characteristic vegetation is composed largely of spinose and switch-like forms in which the chief development has been toward restriction and induration [hardening] of surfaces; a result attributable to the degree of aridity, the seasonal distribution of the rainfall, and also to the intervention of great climatic oscillations.”
When MacDougal wrote this, the Cretaceous period, the late dinosaur age, was still thought to have ended a few million years ago in accordance with Lord Kelvin’s hundred-million-year-old planet. If desert plants had evolved in a few million years, the gradual Darwinian process seemed inadequate to explain them:
The view that such forms are of recent origin, that is since the Cretaceous Period within the present period of advancing desiccation, would predicate a very great phylogenetic activity.
Adaptation, therefore, furnishes but an insecure basis upon which to found a theory of the origin and development of any flora, inclusive of those inhabiting arid regions. The influence of external conditions upon the germ plasm, however, has been seen to produce irreversible changes in a hereditary line by which new combinations of qualities and new characters were called out, which were fully transmissible.
MacDougal inferred that desert plants were the product of environmentally induced genetic mutations: “Gradual modifications by which a long series of forms, each slightly different than its immediate progenitors, appear to have been found among animals, but with plants no such series has been brought to light. These organisms, on the contrary, exhibit sports or saltatory [sudden] derivatives which now have been seen and recognized in a number of species. Such mutants are now occurring, and we may predicate with certainty that they have occurred with normal frequency during the formation of the deserts of southwest America.”
So, instead of invading from older deserts to the south as drying climate drove Asa Gray’s lush Arcto-Tertiary flora north, the ancestors of California’s cactuses and other desert plants might have already lived in California, where they could have mutated rapidly to adapt to the new conditions. A better manifestation of the “hopeful monster” idea than cactuses would be hard to imagine, from a cactus’s viewpoint, at least.
The problem with this scenario was that fossils of the presumed ancestral plants were unknown. MacDougal was aware that most fossils in California desert are of organisms that lived in ancient seas or lakes rather than dry land. Still, he didn’t think that precluded desert origins within the region. Desert plant fossils could be expected to turn up eventually: “It is true, of course, that desert conditions are not favorable for fossilization, yet many opportunities for such action undoubtedly occur in the carrying and burying action of the torrential floods of desert streamways while wind blown deposits might preserve the more indurated forms. Many of these and the skeletons of the Cactaceae would seem well adapted to preservation in this manner.”
Yet when plentiful land fossils did turn up in the Mojave two years after MacDougal proposed his mutant desert genesis, they weren’t what he’d anticipated. In 1911, geology students who had been studying strata around Barstow and Red Rock Canyon began bringing ancient bones to John Merriam, the first professor of paleontology at UC Berkeley. Not to be confused with the Death Valley Expedition’s C. Hart Merriam, he also explored California’s remotest places, but for extinct instead of living fauna. He’d already found some of the oldest known fossil reptiles in the Klamath Mountains. In 1915, after excavating more of the California desert bones, Professor Merriam wrote: “With the exception of the John Day region of eastern Oregon, the largest part of our knowledge of mammalian life west of the Wasatch [the Rockies] is obtained in the heretofore unexplored deposits of the Mohave Desert. At the present time, there are available from the Mohave at least three extinct mammal faunas previously unknown, or only imperfectly known, in the Great Basin.”
The faunas dated from the Miocene epoch, halfway between the dinosaur age and the present, and from the subsequent Pliocene epoch just before the ice age, so they might have been expected to throw at least some light on desert origins. They included some animals that inhabit California desert now—rabbits, pronghorns, foxes, tortoises—and a few that live in deserts elsewhere—camels and peccaries. But they also included creatures that would be bizarre in today’s Mojave—mastodons, at least four horse species, saber-toothed cats, large dogs, and extinct ungulates called oreodonts. It was confusing: “In a few strata abundant remains of fresh-water mollusks indicate deposition of these beds in fresh-water ponds or lakes. At other levels the skeletons of large desert tortoises and numerous remains of land mammals now characteristic of flat open country suggest accumulation upon dry land.”
Some of Merriam’s colleagues thought the fossil faunas could have inhabited a desert. But he doubted it, bearing in mind the prevailing idea that the West Coast’s mountains began to rise and form a “rain shadow” by cutting off oceanic precipitation only in the late Pliocene epoch. This implied that southeast California had been more low lying and level before, more like today’s Great Plains or other grasslands. In any case, Merriam found no fossils of cactuses or other desert plants buried with the mastodons and horses. “As nearly as the writer can judge,” he wrote, “the climate conditions in the Mohave area through the period in which the mammal beds were being laid down, were those of a semi-arid region somewhat more humid than the Mohave today, and the climate corresponded approximately to that now obtaining in the southern end of the Great Valley of California.”
It seemed that William Manly and John Fremont had discovered the Mojave too late. According to Merriam, it once had been just such a pastoral paradise as the pioneers craved. True, his reports on the Miocene and Pliocene faunas included no mention of grass fossils—or any plant fossils to speak of. Merriam complained that they had found no fossil sites where ancient streams had carried material down from adjacent hills. Since vegetation is often richer on highlands than plains, that might have provided more information on the flora. But the Sphinx, having released the tantalizing bones, resumed a retentive silence.