The Reluctant Mr. Darwin (22 page)

It was an emergency hedge, and not very persuasive. There was a much better answer to Jenkin's criticism, but that would become available only later, with the rediscovery of work by Gregor Mendel.

The unkindest cut against natural selection was delivered by Alfred Wallace, of all people, more than a decade after their joint publication. By then Wallace had been home from the East for seven years and written a magnificent book of travel reportage and natural history,
The Malay Archipelago
(published in 1869). He had also solidified his friendship with Darwin. He never became one of Darwin's close confidants, like Hooker or Fox, but he was a very special colleague: the co-discoverer and co-defender of the notorious theory. Apart from Darwin himself, no one understood natural selection better or applied it more forcefully than Wallace. His zealotry, in fact, sometimes surpassed even Darwin's. Wallace saw natural selection operating in certain cases—the gaudy plumage of male pheasants, for instance—where Darwin favored a different causal mechanism. (Darwin's alternative was
sexual
selection, the idea that runaway preferences by the opposite sex, not imperatives of survival, are what drive such gratuitously elaborate modifications.) Despite his strong intellectual commitment to the theory, Wallace evidently felt no urgency about asserting his own claim of authorship. He barely mentioned natural selection in
The Malay Archipelago
, and then with modesty approaching coyness, as an idea “elaborated by Mr. Darwin in his celebrated
Origin of Species
.” A year later, he reprinted his Linnean Society paper, as well as the “law” paper of 1855 and several others, in a volume he called
Contributions to the Theory of Natural Selection
, of which the title seems to reflect how he viewed himself: as a contributor to Darwin's theoretical breakthrough. Wallace waited until 1889 to produce a full-length volume on the subject, that one abnegatingly titled
Darwinism: An Exposition of the Theory of Natural Selection with Some of its Applications
. He was an independent-spirited man but, excepting a few circumstances, he remained faithfully subordinate to Darwin and Darwin's idea. The most notable exception came in early 1869, when Wallace unexpectedly dissented on a crucial point, asserting that natural selection couldn't account for the human brain.

Wallace's apostasy may have reflected other changes in his own life and interests since returning to England. Always eclectic, impetuous in his enthusiasms, he had gotten interested in spiritualism and begun attending séances as an avid believer. During one spooky session with a medium, he'd heard his dead brother Herbert rap out a coded hello from the beyond. Spiritualism was enjoying a boom in popularity at the time, thanks presumably to its combination of vulgar metaphysics, nostalgia for the dearly departed, and parlor entertainment in an era before television. Some scientists saw it as a harmless fad, or else as contemptible bunkum, but to Alfred Wallace it was a new horizon in anthropology. Although not religious in any conventional sense, he concluded that there was more to this world than physical causes and effects. His new credence didn't collide openly with his older views until April 1869, when
The Quarterly Review
carried an essay by him, mostly focused again on Lyell's geology, in which Wallace pointedly digressed to the subject of natural selection. That mechanism couldn't have produced the human brain, he wrote, let alone the “moral and higher intellectual nature of man.” Of course the living world is governed by laws, Wallace noted. But he himself was now inclined to believe “that an Overruling Intelligence has watched over the action of those laws, so directing variations and so determining their accumulation” as to yield the loftier, more wondrous human capacities.

Darwin knew the article was coming and, a month earlier, had told Wallace with nervous good cheer: “I shall be intensely curious to read the
Quarterly
. I hope you have not murdered too completely your own & my child.” In the event, it was as bad as he feared: intellectual infanticide. Natural selection as Darwin (and Wallace too?) had originally conceived it was meaningless if “an Overruling Intelligence” overruled the haphazardness of the variations, directing them toward foreordained purposes. In the margin of his copy, Darwin scratched “No!!!”

38

Discomfort with natural selection, working crosswise to the general acceptance of evolution, pushed biologists during the late nineteenth century toward alternate explanatory mechanisms. Some of those biologists looked backward in time, and to France, for a revival of Lamarckism. Some embraced other evolutionary theories, various in their particulars but with enough common elements to be lumped under two labels, “orthogenesis” and “saltationism.” All three—orthogenesis, saltationism, and revived Lamarckism—came on strongly during the 1880s and 1890s, a slump period for Darwin's reputation. A historian of evolutionary thought named Peter J. Bowler has nicely charted these currents in several of his books, including one titled
The Eclipse of Darwinism
. Bowler's research corrects the misconception that, after publishing
The Origin of Species
, Charles Darwin rode to glory in a flaming chariot. No, he sat parked on a siding.

The new Lamarckians didn't entirely reject Darwin's big idea, but they considered it small. Okay, they allowed, maybe natural selection does play a marginal role in fine-tuning adaptations, but it can't explain the origin of variations or the dramatic trends and patterns of evolutionary change. Selective in their definition of Lamarckism, they also largely ignored Lamarck's own woozy notions about “subtle fluids” and a “feeling of existence,” preferring two other items from his cornucopia of theory: the parallel progression of independent lineages from simple to complex (that is, the prairie-grass model of biological diversity, as opposed to the branching-tree model) and the inheritance of acquired characteristics. They emphasized the role of environmental conditions in eliciting need-directed variations (not undirected ones, as Darwin had it) which, so they believed, are heritable. They also inclined toward the view that long-term evolutionary trends are linear, triggered by environmental conditions and driven onward by habit, and by the inheritance of what habit produces. Horns get bigger, from species to species over millions of years, because animals use them when they smack heads. The fossil record yields other examples of such linearity, supposedly transcending the immediate adaptive needs of each individual creature and expressing inherent trends throughout the history of a lineage. Direct influences from the environment might account for the small-scale changes and adaptations, while continuous habit or some mysterious force drives the long-term trends.

There was no perfect consensus, though, among the new Lamarckians. Paleontologists tended to see the long, linear trends; field naturalists and lab experimenters tended to see, or imagine they saw, the inheritance of acquired characteristics. The whole school of thought was especially strong in America, where a naturalist named Alpheus S. Packard, Jr., called it neo-Lamarckism.

Packard, like other influential neo-Lamarckians of his generation, had been trained by Louis Agassiz, the Swiss-born naturalist who ruled in professorial majesty at Harvard's Museum of Comparative Zoology. Agassiz was a brilliant but obdurate man, an essentialist who detested evolutionism—Darwin's brand in particular—and clung to a vision of well-ordered nature assembled by special creations. The zoology of Agassiz was consonant with the natural theology of William Paley. Agassiz's livelier students, such as Packard, did cross the line to accept evolution in principle, but even they mostly retained the old man's distaste for Darwin's cold, hard mechanism. Packard began seeing what he thought were Lamarckian phenomena during his study of the horseshoe crab,
Limulus polyphemus.
Then he turned to the blind insects and other dark-dwelling animals of Mammoth Cave, in Kentucky, concluding that their loss of eyesight (in some cases, of eyes altogether) results from disuse, followed by shrinkage of visual organs, followed by inheritance of the shrunken forms. Although Darwin himself had admitted a secondary role for use and disuse, the evidence from Mammoth Cave struck Packard as “Lamarckism in a modern form.” That explanation seemed to him “nearer the truth than Darwinism proper or natural selection.”

Among the American paleontologists was another Alpheus (you can't tell them without a scorecard), also trained at Harvard by Louis Agassiz: Alpheus Hyatt. From his study of ammonoids and other fossil invertebrates, Hyatt concluded that evolution is an additive developmental process—one that proceeds by the addition of new adult characteristics onto older sequences of development. Adding such characteristics, Hyatt thought, somehow compresses the more primitive traits backward into earlier embryonic stages. This idea became known as “the law of acceleration,” suggesting that speedier growth through the earlier stages allows for the additional complexity in adulthood. What's the source of those newer, more complex characteristics? After some hesitation, Hyatt accepted the Lamarckian view that they are adaptive adjustments to environmental stresses, acquired as habits and then inherited.

Edward Drinker Cope, an American paleontologist working on vertebrate fossils, arrived at the law of acceleration independently. Like Hyatt, he saw long-term linear trends in fossil sequences—new modifications added onto older forms in a steady, directional way—and, again like Hyatt, became convinced that the inheritance of characteristics acquired in response to environmental conditions is what best explains them. In 1877, Cope published a book,
The Origin of the Fittest
, combining Darwin's own title with Herbert Spencer's vivid phrase (“the Survival of the Fittest”) to impute that Darwin hadn't dug deeply enough into the subject. Like the other Alpheus—that is, Alpheus Packard—Cope granted that natural selection might play some part in culling inferior individuals, but he figured it couldn't be more than secondarily important, because it didn't explain the source of variation. Lamarckism, Cope thought, did.

In England, Herbert Spencer himself had espoused a theory of evolution (he called it “the development hypothesis”) as early as 1852, seven years before Darwin's book. Spencer was no biologist; he worked as a journalist, became prominent as a pop philosopher, and picked up his evolutionary ideas from reading Lyell's dismissive account of Lamarckism (which turned him, perversely, toward Lamarck) and the mystery bestseller of the day,
Vestiges
. His own writings about evolution were grandiose and murky, detached from the sort of empirical detail that Darwin offered abundantly. But the subject gave Spencer's works on political philosophy and sociology a yeasty fluff, especially when he linked his advocacy of laissez-faire individualism to notions of evolutionary progression; and he sold well. Some scholars credit (or blame) Spencer for launching the intellectual movement misleadingly known as Social Darwinism, and for transmitting it to America through his publications and, more personally, during a visit in 1882. The steel magnate Andrew Carnegie read both Spencer and Darwin, finding luminous reassurance in being told that harsh competition is a constructive law of nature. By then Spencer himself had emerged as a neo-Lamarckian, and arguably a social neo-Lamarckian, too. In a choice between natural selection of undirected variations, on the one hand, and heritable advantages gained through striving, on the other hand, the latter fit better with his ideas about self-advancement. Onward and upward for ambitious men and their scions! Eleven years after Darwin's death, Spencer made it explicit with an essay titled “The Inadequacy of Natural Selection.”

The list of notable neo-Lamarckians in Britain and Europe also included Arthur Dendy (a paleontologist), Samuel Butler (a novelist and argumentative proselytizer), George Henslow (a clergyman-naturalist, who wrote a book about the “self-adaptation” of plants to their living conditions), Joseph T. Cunningham (a marine biologist, who studied color change in flatfish), Peter Kropotkin (a Russian aristocrat turned socialist, who argued that cooperation among animals, as a heritable habit, might be more important than natural selection), C. E. Brown-Séquard (known for his experiments inducing heritable epilepsy in guinea pigs), and the zoologist Theodor Eimer. By the end of the 1880s, as Samuel Butler gloated, nearly every issue of the journal
Nature
(founded by Darwin allies in 1869) contained something on Lamarckian inheritance.

Theodor Eimer, professor of zoology at Tübingen, Germany, was an important transitional figure between neo-Lamarckism and another non-Darwinian school of thought, for which Eimer himself popularized the label “orthogenesis.” Early in his career, Eimer studied wall-climbing
Lacerta
lizards on the island of Capri. Later he investigated the color patterns of butterfly wings. In the first of his two major volumes on evolution, published in 1888 as
Entstehung der Arten
(with an English edition soon afterward, translated as
Organic Evolution
), he combined a Lamarckian view of character acquisition with a claim that internal “laws of growth” dictate the characteristics to be acquired and, over the long term, the direction in which evolution goes. For certain traits, the direction might be neutral—or worse—with regard to adaptation. The word “orthogenesis” means growth in a straight line. It implies an inherent tendency of some sort, expressed ever more extremely in one descendant after another and independent of the creatures' immediate needs. This view became popular among paleontologists (including Cope and Hyatt in America) as an explanation of certain linear trends in the fossil record, some of which appeared not just non-adaptive but destructive. The Irish elk,
Megaloceros giganteus
, is one famous example of what supposedly can result from orthogenesis; its antlers grew so oversized that they seemed to have doomed the species to extinction. Eimer saw similar phenomena, he thought, among butterflies. His studies of Lepidoptera convinced him, says Peter Bowler, “that the actual course of orthogenetic evolution was completely predetermined by the internal predisposition to vary in a particular direction.”