Coming of Age in the Milky Way (35 page)

The first premise has to do with
variation
. It notes that each individual member of any given species is different—that each, as we would say today, has a distinct genetic makeup. Darwin understood this very well. He grew up at a time when animal breeding and plant hybridization was booming in England—his father-in-law, Josiah Wedgwood, the ceramics manufacturer, was a noted sheep breeder, and his father was a pigeon fancier—and he learned from the husbanders to pay attention to the often subtle individual characteristics that they sought to quash or to perpetuate.
^*
Grounded
in the specifics of biological variety, Darwin’s thought was a mosaic of the particular: Scores of his publications consists of little notes in the
Gardeners’ Chronicle and Agricultural Gazette
and the
Journal of Horticulture and Cottage Gardener
asking such questions as, “Has any one who has saved seed Peas grown close to other kinds observed that the succeeding crop came up untrue or crossed?”
¹³
and, “Is any record kept of the diameter attained by the largest Pansies?”
¹⁴

Darwin’s second premise is that all living creatures tend to produce more offspring than the environment can support. It’s a cruel world, in which only a fraction of the wolves and turtles and dragonflies that come into existence manage to find sustenance and avoid predators long enough to reproduce. The English economist Thomas Malthus had quantified these harsh facts of life by pointing out that most species reproduce geometrically, while the environment can support no better than a linear increase in their populations.
^*
Darwin read Malthus’s
An Essay on the Principle of Population
in London in 1838—“for amusement,” he recalled—and the hypothesis of evolution by natural selection began to take form in his mind. “One may say,” he wrote, that “there is a force like a hundred thousand wedges trying [to] force every kind of adapted structure into the gaps in the [e]conomy of nature, or rather forming gaps by thrusting out weaker ones.”
¹⁵
It was in the combination of the boundless fecundity of living things with the limited resources available to support them that Darwin found a natural, global mechanism that worked constantly to extinguish most variations, preserving only those carried by individuals who managed to survive and reproduce.

Which leads to the third premise—that the differences among individuals, combined with the environmental pressures emphasized by Malthus, affect the probability that a given individual will survive long enough to pass along its genetic characteristics. This is the process that Darwin called “natural selection.” White moths fare better in snow, where their coloration serves as camouflage and
protects them from predator birds, while brown moths do better in snowless autumnal forests, where their color blends in against the brown tree trunks.
^*
It is in this sense that the “fittest” (the phrase is Herbert Spencer’s) survive, not because they are in some sense superior to their colleagues, but because they better “fit” their environment. When environmental conditions change, the most exquisitely adapted individuals may suddenly find themselves no longer fit; then it is the freaks and misfits who inherit the future.

Darwin’s conclusion was that natural selection leads to the origin of new species. Because the world is constantly in a state of change, nature favors the varied—a community of predominantly white moths is better off if it contains a few dark moths, against a smoggy day—and the geographically dispersed, those who do not keep all their eggs in one basket. As a result, the degree of individual variations found within a given species tends to increase with the passage of time, until some groups have become so different from others that they can no longer mate and produce fertile offspring. At that point, a new species has emerged. As Darwin wrote:

Darwin noted that in some ways his theory recalled the biblical image of the Tree of Life. But now the tree, instead of being static as in the creationist view, had come alive and was still growing:

Critics with a preference for Bible stories complained that natural selection was cold and mechanical. But in Darwin’s eyes it both animated and illuminated the natural world:

And he added, in what was to become an evolutionists’ credo:

Darwin had formulated the essential elements of his theory by the time of his marriage in 1839, and by 1844 had outlined it, in a 230-page essay. Yet he withheld it from publication for the next fifteen years. While the essay lay in his desk drawer, accompanied by strict instructions to publish it in the event of his death, Darwin settled in the country, fathered ten children, corresponded with Lyell and a hundred other scientists, and wrote books—among them a journal of the voyage of the
Beagle
, an account of his theory of coral reefs, a treatise on volcanos and another on the geology of South America, and a masterful study of barnacles that consumed seven years of work and left him fuming that “I hate a barnacle as
no man ever did before.”
²⁰
In all, Darwin kept his theory of evolution a secret for nearly as long as Copernicus had concealed his heliocentric cosmology. Why the delay?

One explanation, still sometimes put forward, is that Darwin was constantly ill. This will not wash. Ill he certainly was: From about the time of his marriage and probably long before he was subject to intense headaches, vomiting, and heart palpitations. He consulted the best doctors in England in search of a cure, had himself hypnotized, and resorted to hydrotherapy, spending winter days wrapped in a cold, wet sheet. “His life,” wrote his son Francis Darwin, “was one long struggle against the weariness and strain of sickness.”
²¹
The ailment was never conclusively diagnosed and has since been attributed to many agencies, from Chagas’ disease, brought on by what Darwin called the “attack (for it deserves no better name) of the Benchuca, the great black bug of the pampas” on March 26, 1835, to the psychosomatic affects of internal conflict between this former candidate for the priesthood and the anticlerical implications of his own theory. A more likely if less colorful possibility is that he suffered from severe allergies. But in any case, illness alone cannot explain why Darwin suppressed the theory of natural selection, since during those same years he wrote prolifically on other subjects.

It is much more likely that Darwin feared the storm of opposition he knew his ideas would provoke. He was a gentle, straightforward, almost childishly simple man, habitually respectful of the outlook of others and disinclined toward disputation. His theory, he knew, would draw down fire, not only from the clergy but from many of his fellow scientists as well.

The religious opposition promised to be formidable. Darwin did not have to strain his imagination to foresee what the orthodoxy would make of his assertion that animals and men are kin and that chance mutations drive evolution; to advocate such a thing, he told his friend Joseph Hooker, would be like admitting to a murder. (The murder of Adam, it was to be called.) Nor did he need look beyond England to envision what lay in store for him once word of the theory got out. When William Lawrence, later president of the Royal College of Surgeons, suggested that man evolves through the inheritance of innate rather than acquired traits, the Lord Chancellor declared his book contrary to Scriptures and denied it copyright.
The legendary erudition of Benjamin Jowett of Oxford is recalled in a famous Balliol College masque’s quatrain:

But when Jowett in 1855 published a controversial interpretation of the Epistles of Saint Paul, he was accused of heresy and his salary was frozen. Darwin, puttering happily with wormstones and petunias in gardens that his insight rendered luminescent as Eden, was not eager to see the day when a thousand country parsons would turn his name into a synonym for the antichrist.

The scientific opposition arose in large measure from professional disdain for the very concept of evolution, which had long been an enthusiasm of ecstatics and occultists devoted to seances and tales of fairies flitting across the moors at dawn. To advocate so amateurish a theory was to invite learned ridicule. When in 1844 a theory of evolution was championed in the anonymous and enormously popular
Vestiges of the Natural History of Creation
, the book was pilloried by such authorities as the Cambridge mineralogist William Whewell (of whom it was said that “science was his forte, omniscience his foible”), the astronomer John Herschel, and the geologist Adam Sedgwick, who devoted eighty-five pages of the
Edinburgh Review
to its demolition (and who, indeed, was to subject Darwin’s book to comparable scorn once it finally appeared).

Against these forces Darwin, like Copernicus, would have to defend a theory that he knew to be incomplete, for neither he nor anyone else understood the micromechanism of heredity. “The laws governing inheritance,” as Darwin admitted, “are quite unknown.”
²²
Missing was proof of the existence of the fundamental hereditary unit, the biological quantum—in short,
the gene
. Without the stability imparted by genes, innovative mutations would be diluted away like drops of blood in the ocean, before they had time to spread to any significant numbers of individuals. In such a situation natural selection might occur, but it could scarcely account for the origin of species.

The first evidence of the existence of genes did not appear until
1866, eight years after Darwin was obliged to publish
The Origin of Species
, when the Moravian monk Gregor Mendel published the results of his extensive experiments with green peas in the garden of an Augustinian monastery—results that demonstrated the requisite persistence of the quanta of heredity—and Mendel’s findings were in any event universally ignored until attention was called to them in 1900, by which time Darwin was dead. Darwin sought to make up the deficiency by proposing a theory of “pangenesis” to account for the transmission of hereditary traits, but he remained sensitive to his vulnerability on this count. As he once remarked, he appreciated the shortcomings of his theory better than did most of its censurers.

It was, then, a reluctant Darwin who at Lyell’s urging finally began writing an exhaustive account of the origin of species through natural selection. He intended it to be a massive tome, the completion of which could safely be expected to take years; perhaps, like Copernicus, he would not have to live to read the reviews. But then, on June 3, 1858, when he had written only the first few chapters, everything changed. A letter bearing the postmark of the Malay Archipelago arrived at Darwin’s home. It came from the naturalist Alfred Russel Wallace. It contained the draft of an essay by Wallace titled, “On the Tendency of Varieties to Depart Indefinitely from the Original Type.” Wallace asked for Darwin’s reactions to the paper.

Darwin had a reaction, all right, and it was one of horrified astonishment: The theory outlined in the essay was identical to Darwin’s own. “I never saw a more striking coincidence,” he wrote to Lyell that afternoon.
²³

Wallace, like Darwin, was an indefatigable collector of plants and insects.
^*
He, too, had been impressed by reading Lyell’s book, had long pondered “the question of
how
changes of species could have been brought about,” and had hit upon the answer after reading Malthus. He was, he recounted, recovering from malaria when “it suddenly flashed upon me that … in every generation the
inferior would inevitably be killed off and the superior would remain—that is, the
fittest would survive
(Wallace’s italics).
²⁵
Wallace drafted the theory in three nights and sent it by the next mail to Darwin, who was known in scientific circles to have some sympathy for the hypothesis of evolution.