One reason why Darwin found the Galapagos Islands “very sterile” was that most of their terrain is recently erupted lava: “Nothing could be less inviting than the first appearance. A broken field of black basaltic lava, thrown into the most rugged waves, and crossed by great fissures, is every where covered by stunted, sun-burnt brushwood, which shows little signs of life.” He agreed with the Beagle’s captain, Robert FitzRoy, that the lava gave the islands an infernal aspect, making their swarms of blackish marine iguanas seem like imps of darkness on the shores of Pandemonium despite the big lizards’ inoffensive diet of seaweed.
Lava flows are a feature of California’s deserts, and I can understand Darwin’s impression. Whether thrusting out of the ocean or smeared across continental mesas, they can indeed seem hellish. A closer look at Cinder Cone Lava Beds in the Mojave National Preserve gave me a somewhat different impression than Darwin’s, however. The beds looked infernal enough from a distance, but when I got into their complex of box canyons the landscape began to seem almost cozy.
Floods and wind had abraded the lava to a smoothness that felt silky in the fresh April air. Sun-warmed black chunks protruding from the white sand of the washes made comfortable recliners. The cubical basalt ledges above were like the remains of cyclopean walls, stairways, corridors, and antechambers, but without the disturbing grotesqueries of Red Rock Canyon’s hoodoos. Although the lava blocks seemed good habitat for the fat black chuckwallas that might have mimicked Darwin’s marine iguana imps, I didn’t find the big lizards there.
The lizards I did find didn’t seem ugly, lazy, or stupid, but graceful, busy and rather astute. Passing a fragrant shrub with purple flowers full of bees, I saw a pale shape zip out of its shade and then apparently disappear. I kept watching, and eventually a zebra-tailed lizard that had blended with the sand when it stopped running decided to move again. It raised its tail and sped toward a cheesebush, where it began swelling out its throat and doing push-ups that flashed a bright blue patch marked with two black bars on its flank.
Soon, another smaller zebra-tailed lizard seemed to get the message, since it emerged from a nearby shrub and dashed away. Then another, slightly larger one emerged from the cheesebush and started wriggling the tip of its tail as though to get the first lizard’s attention. Clearly attracted by this “come-hither” gesture, the first lizard obligingly approached and began swelling its throat and doing push-ups again, watched intently by the newcomer. Before very long, they ran into the cheesebush together.
The trio clearly had exchanged a lot of information. April is a benign time of year, of course, but even so the lizards seemed much more concerned with their effects on each other than with the desert’s effects on them. Competition evidently was underway, although whether for space or sex, or both, was unclear. Indeed, the competition was more conspicuous than it would have been in woods or grassland. Darwin’s evolutionary backwater assumptions about desert didn’t seem upheld.
Those assumptions weren’t universally upheld even in the nineteenth century. When Darwin’s friend and supporter, the Harvard botanist Asa Gray, published a survey of North American vegetation in 1884, he followed Darwin’s lead in attributing a recent rise to the Americas’ western mountains. But he assigned an active evolutionary role to desert life. He wrote that “the peculiar elements of the California flora, and also of the southern Rocky Mountain region and the Great Basin” probably had originated in “the Mexican Plateau.” That flora had then spread north and—because of growing aridity as the West Coast mountains rose within the past few million years—replaced what he called an “Arcto-Tertiary” flora of temperate conifers and hardwoods that had covered much of the Northern Hemisphere since the dinosaur age.
Gray was ambivalent about natural selection’s role in this northward spread of desert. He thought that “competition from the Mexican Plateau vegetation” had contributed to the Arcto-Tertiary forest’s demise in the Southwest, but added: “It is unnecessary to build much upon the possibly fallacious idea of increased strength gained by competition. Opportunity may account for more than exceptional vigor.” Without the opportunity of drying climate, in other words, cactuses and creosote bushes wouldn’t have been much competition for aboriginal conifers and hardwoods.
Gray’s ambivalence about competition reflected increasing doubts about Darwinism toward the nineteenth century’s end. Natural selection seemed too random and cumbersome to have produced living organisms’ exquisite adaptations, especially after 1866, when the leading English physicist William Thomson, later Lord Kelvin, “proved,” from the rate at which the earth’s molten center was thought to be cooling, that the planet could not be much more than a hundred million years old. Given such a restricted time frame, many naturalists looked with renewed interest on the idea of Enlightenment savants like Lamarck that environment might have direct effects in changing organisms.
The Reverend George Henslow, a botanist and nephew of one of Darwin’s university professors, used desert as a case in point for a more direct and prompt cause of biological change. Noting Darwin’s reticence about desert, Henslow wrote: “He bases his theory of Natural Selection on the struggle between living organisms, and to a much less degree on the environment. My contention is that precisely the reverse really obtains; that morphological adaptations arise, and are maintained—not in consequence of any struggle with other living beings of the same or of different species—but solely through the direct action of the new environment.”
Henslow thought desert plants’ thorniness, leaflessness, and hairiness demonstrated those features’ environmentally induced origins: “We thus begin to suspect, indeed very strongly, that the various peculiarities (such e.g., as the densely hirsute clothing and the consolidation of the vegetative tissues) are the direct result of the dry climatic conditions surrounding the plants, and that the unfavorable environment actually brings about the production of just those kinds of structures which are best able to resist the injurious effects of climate, and so enables the plant to survive under them.”
Another reason scientists backed away from Darwin was that he couldn’t supply a credible mechanism whereby organisms might produce and transmit the variation upon which natural selection could work. As one anti-Darwinian, the American naturalist Edward D. Cope, complained, natural selection alone might explain the “survival of the fittest,” but it didn’t explain the “origin of the fittest.” It might explain why cactus replaced broadleaf trees in desert; it didn’t explain how cactus developed succulence, spines, and other variations useful in dry climate.
If desert plants became succulent or spiny simply because the heat and dryness affected them that way, as Reverend Henslow maintained, then that supplied at least part of the mechanism. But Henslow’s idea had a problem. Cactuses grown in moist gardens or hothouses reproduce little cactuses as spiny and succulent as their parents, so these traits, even if dryness originated them, somehow have become inheritable. Many nineteenth-century scientists, including Cope, also adopted the Lamarckian idea that acquired traits might be inherited, thus completing a mechanism for variation.
Cope conceived elaborate “neo-Lamarckian” theories about the acquisition and inheritance of variations, although, being a zoologist, he did not apply them to desert bushes. In fact, he was the “founder of American herpetology,” the first in the United States to study reptiles and amphibians systematically. His live-in lab contained a cold-blooded menagerie, including a Gila monster that apparently liked to have its head scratched. Cope frequently collected in the Southwest, and he described many species. He was so adept at this that he once classified a newly discovered lizard by simply examining it in another naturalist’s hand. He was a paleontologist too. He described the first North American fossil “lacertilian” from an early Age of Mammals deposit in the West in 1867. Another paleontologist, Joseph Leidy, had described lacertilian fossils earlier, but they’d turned out to be dinosaur bones once the distinction between lizards and dinosaurs (unknown to Darwin when he visited the Galapagos in 1835) became evident.
Cope might have used reptile herbivores like those in the arid Galapagos to argue against Darwin’s tacit assumption that evolution would be slow in desert. According to his anti-Darwinian “origin of the fittest” theories, a small omnivorous animal like a lizard might become a larger herbivorous one more quickly than natural selection alone would allow. Finding itself in a place like the Galapagos without large mammal herbivores, it would not simply continue its modest omnivory, but would begin to eat more plants, a process Cope called “archaesthicism.” This change of diet would affect its anatomy—jaws, teeth, digestive system, even size—a process Cope called “kinetogenesis.” Then it would bequeath these new traits to its offspring through “recapitulation,” whereby changes in the parent’s body would affect the embryo.
Cope might have pointed out, furthermore, that Darwin’s belief that the volcanic Galapagos rose from the Pacific fairly recently implied that the islands’ unique reptiles had evolved their unusual traits not slowly, but quickly. (Darwinism’s leading American foe, Harvard biologist Louis Agassiz, visited the Galapagos in 1872 and cited their recentness and unique biota as evidence against gradual natural selection.) Cope then could have posited a similar evolution for the North American desert’s plant-eating lizards. Most large mammal herbivores might have died out as scattered, spiky bushes replaced Asa Gray’s lush Arcto-Tertiary vegetation, providing an opportunity for reptiles to eat more plants and grow larger. Six-inch insect-eating lizards could have become eighteen-inch chuckwallas in a few hundred thousand years.
Scientific competition, however, came between Cope and thoughts on desert evolution. His 1867 lizard fossil was so fragmentary that it was assigned to a better-preserved genus that another paleontologist, Othniel C. Marsh, found and named in 1871. A wealthy Yale University professor, Marsh could exploit western fossil deposits with large, well-funded expeditions, while Cope, usually self-employed, had to explore alone or with a few underpaid assistants. Cope envied Marsh’s prominence; Marsh envied Cope’s brilliance. Their rivalry grew so intense that it descended to ad hominem newspaper attacks and spying on each other’s collections and fossil sites.
Marsh’s 1871 discovery did briefly spur the rivals’ fossil lizard collecting, as Charles Gilmore, a Smithsonian herpetologist observed: “Owing to the continued exploration of the Eocene of the Bridger Basin in southeastern Wyoming and of the Oligocene deposits in northeastern Colorado by Cope and Marsh, knowledge of the extinct lizards increased more rapidly in the two years following, 1872 and 1873, than in any other similar period in the entire history of the country. No less than 10 genera and 26 species were established by Leidy, Cope and Marsh, within this period.”
But neither Cope nor Marsh did more than describe, name, and classify their fossil lizards. They were much too busy using more impressive fossils to promote their clashing agendas. Cope applied his ideas about omnivores quickly evolving into herbivores not to lizards but to mammals. He thought they had been largely arboreal when the dinosaurs ruled (he and Marsh were the first to discern the basic outlines of dinosaur evolution), and then had descended from the trees and evolved into large ungulate herbivores after the dinosaurs’ extinction. Marsh was a confidant of Darwin and T. H. Huxley, who furthered their agenda by finding and publicizing important “missing links” between groups of organisms. He used his huge fossil collection to develop a Darwinian lineage of horse evolution that made him famous, to Cope’s chagrin, and is still used in biology classes.
Despite their differences, both paleontologists’ primary criterion for measuring evolutionary development was the anthropomorphic one of brain growth. Cope thought mammal brains had grown through inheritance of traits acquired by interaction with the environment. Marsh thought they had grown through natural selection of larger-brained individuals. Neither man applied such progressive notions to reptiles that Darwin had dismissed as stupid. Cope read and admired The Voyage of the Beagle at an early age, and its disdain for desert perhaps influenced him. A comment he made about crossing the Great Basin Desert on a train was typical: “It was very hot and dusty and I do not wish to visit such a country in the summer. One has alkali, sage brush and grease wood and vice-versa, all the way.” His trips to the Southwest often continued into Mexico’s tropical forests, which he described almost as ecstatically as Darwin had the Amazon.
Cope published a 1,117-page tome on North American reptiles that noted chuckwalla and desert iguana plant eating but failed to consider its origin. Marsh was interested in lizards mainly as a way to annoy Cope. In 1872, when their rivalry reached one of its periodic peaks (they would squabble until both died in the 1890s), the Yale professor described sixteen new species in five genera of fossil lizards he’d found on his 1871 expedition. One of his genera, Oreosaurus, included several species that Cope placed in a genus of his own, Xestops. Cope’s pride in his classifying skills made such coining of rival names a sure way for Marsh to torment him.
Marsh’s sixteen new species manifested another reason beside backward brains for the rivals’ lack of interest in lizard evolution. Whereas many of their early mammals could be traced through fossil links to familiar living beasts like horses, only one of the fossil lizards they found seemed to have a living relative in North America, the Gila monster of the genus Heloderma. The rest belonged to groups of uncertain identity. A decade after Marsh’s annoying Oreosaurus publication, this uncertainty allowed Cope to have the disparaging last word on his rival’s fossil lizard species: “As Professor Marsh does not give us any clue as to the affinities of these forms, they cannot be considered further.”
The two paleontologists’ bad attitudes seem to have set the tone for early lizard evolution studies. Charles Gilmore noted that not even Cope had set out deliberately to find fossil lizards: “All of the fossil lizard remains known from North America, if the Mosasauria [giant marine lizards] are excluded, have been discovered as an incidental part of the work of various expeditions organized either for geological exploration or for the collecting of other classes of fossil vertebrates. Nowhere is there a record of an expedition having as its primary object the securing of lizard specimens.” For decades after Cope and Marsh’s 1870s discoveries, Gilmore lamented, scientists had not described a single new fossil lizard.