The Story of Western Science

by Susan Wise Bauer

  First, That food is necessary to the existence of man.

  Secondly, That the passion between the sexes is necessary and will remain nearly in its present state.

  In other words, humanity has an innate drive to reproduce, which means that the population constantly increases. But because the food supply does not increase as rapidly as the population, a large percentage of those born will always die of starvation: the “difficulty of subsistence” provides a “strong and constantly operating check on population.”12

  This, for Malthus, meant that there would never be such a thing as a perfect society, in which all members live “in ease, happiness, and comparative leisure”; some part of the human race will always be suffering from poverty and hunger. But Darwin was at once gripped by another thought. “It at once struck me,” he later wrote, “that under these circumstances favourable variations would tend to be preserved and unfavourable ones to be destroyed. The result of this would be the formation of new species.”13

  Darwin had found, he believed, the key to the species problem. He mulled it over for some time and in June of 1842 began to work on setting it down in writing. By 1844 he had completed a first draft of the essay that would become On the Origin of Species; a few years later he added to this draft the idea that these variations come about as living creatures adapt to the “economy of nature”—the environment around them.

  But he was not yet ready to publish his argument; and he was still perfecting it when, in 1858, he received a letter from the British explorer Alfred Russel Wallace. Wallace, fourteen years younger than Darwin, had greatly admired Darwin’s Journal and Remarks. He had followed Darwin’s example and taken a field trip abroad—in his case, first to the Amazon rain forest, and then to the East Indies. He had collected his own observations on tens of thousands of different species and had come to a novel conclusion: species change, become different, evolve, because of environmental pressures.

  Wallace, then in Indonesia, had been forced by a recurrent fever to spend hours every day lying down. “I had nothing to do but think,” he later wrote, and one day

  something brought to my recollection Malthus’s “Principles of Population,” which I had read about twelve years before. I thought of his clear exposition of “the positive checks to increase”—disease, accidents, war, and famine—which keep down the population of savage races to so much lower an average than that of more civilized peoples. It then occurred to me that these causes or their equivalents are continually acting in the case of animals also. . . . Vaguely thinking over the enormous and constant destruction which this implied, it occurred to me to ask the question, Why do some die and some live? And the answer was clearly, that on the whole the best fitted live. From the effects of disease the most healthy escaped; from enemies, the strongest, the swiftest, or the most cunning; from famine, the best hunters or those with the best digestion; and so on. Then it suddenly flashed upon me that this self-acting process would necessarily improve the race, because in every generation the inferior would inevitably be killed off and the superior would remain—that is, the fittest would survive.14

  Wallace jotted these insights down into a quick essay, “On the Tendency of Varieties to Depart Indefinitely from the Original Type,” and enclosed it in his letter to Darwin, asking him to pass it on to Charles Lyell, or any other natural philosophers who might find it interesting.

  Darwin was gobsmacked: “This essay,” he exclaimed, “contained exactly the same theory as mine.” As requested, he sent it along to Lyell (“I never saw a more striking coincidence,” he wrote, in his cover letter, “. . . all my originality, whatever it may amount to, will be smashed”), along with a short abstract of his own work in progress.15

  Lyell and his colleague Joseph Hooker, director of the Royal Botanical Gardens and a personal friend of Darwin’s, presented both works to the members of the Linnean Society of London, a century-old club for the discussion of natural history; in August of 1858, Wallace’s and Darwin’s theories were published side by side in the Linnean Society’s printed proceedings.

  This was the first articulation of the theory of evolution by natural selection. It was a watershed moment in natural history, but apparently no one noticed. The president of the Linnean Society famously remarked, in his annual report for 1858, “The year . . . has not, indeed, been marked by any of those striking discoveries which at once revolutionize . . . science.”16

  The following year, Darwin, energized by Wallace’s codiscovery of the principle of natural selection, finally published his entire argument. This first edition—On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, laid out a series of arguments, all supporting Darwin’s main conclusion: that life, no less than the earth itself, is changing constantly, and that natural causes alone account for that change. He had solved the species problem to his own satisfaction: Species were not permanent, fixed, or bridgeless. They appeared when previous species developed variations and those variations proved helpful in the fight for survival.

  On the Origin of Species immediately sold out. The book was widely discussed, widely criticized, widely praised and condemned: “The reviews were very numerous,” Darwin remarked later; “for a time I collected all that appeared . . . but after a time I gave up the attempt in despair.” In 1864 the well-known biologist and philosopher Herbert Spencer used the phrase “survival of the fittest” to describe Darwin’s theory; the phrase soon became inextricably entwined with Darwin’s work.

  Over the next two decades Darwin revised the Origin of Species five times. Even in his final revision, he did not take the theory to its logical end; but he had already privately concluded that his principles of natural selection applied to the human race as well. “As soon as I had become . . . convinced that species were mutable productions,” he wrote in his later Autobiography, “I could not avoid the belief that man must come under the same law.”17 In 1871 he finally published The Descent of Man, an extension of his evolutionary principles to the human race.

  The Descent brought the full implications of the Origin of Species into plain sight.

  Charles Darwin had put biology on a collision course with the human race’s most cherished idea about itself: its uniqueness. “The question raised by Mr. Darwin as to the origin of the species,” one reviewer wrote, “marks the precise point at which the theological and scientific modes of thought come into contact. . . . We are brought face to face in this book with the difficult problems which previously had only revealed themselves more or less indistinctly on the dim horizon.”18

  Those difficult problems were now in plain sight—and would remain there.

  CHARLES DARWIN

  On the Origin of Species

  (1859)

  On the Origin of Species is widely available in many different editions and formats. Check the textual notes; the original 1859 text is the clearest, most succinct, and most easily grasped by the general reader. Many editions of the 1859 text also reproduce the essay that Darwin added to the third (1861) edition, “Historical Sketch of the Progress of Opinion on the Origin of Species,” which lays out his intellectual debt to Lyell, Lamarck, and others; it is brief and worth your time.

  The following recommended edition is simply one of many available, but it does reproduce both the 1859 text and the historical sketch.

  Charles Darwin, The Origin of Species, Wordsworth Editions (paperback and e-book, 1998, ISBN 978-1853267802).

  TWENTY-ONE

  Inheritance

  The laws, and mechanisms, of heredity revealed

  By this process the species A would change into the species B.

  —Gregor Mendel, Experiments in Plant Hybridisation, 1865

  Charles Darwin was sure that variations were passed from parent to child, but he had no idea how this worked. “The laws governing inheritance are quite unknown,” he lamented in the second chapter of the Origin of Species. “No one can say why a peculiar
ity . . . is sometimes inherited and sometimes not so.”1

  The most widely accepted nineteenth-century model of inheritance, “blending,” posed enormous problems for natural selection. It proposed that the characteristics of both parents somehow passed into their offspring and melded together to create a happy medium: a black stallion and a white mare should have a grey foal, a 6-foot father and 5-foot mother should produce a child who would mature at 5 feet 6 inches. There were two problems with blending, though: First, it was (often) demonstrably untrue. Second, it tended to remove variation, not preserve it.

  Nine years after the Origin of Species was first published, Darwin suggested that inheritance could be explained instead through the existence of “minute particles” called gemmules, which were thrown off by every part of an organism, accumulated in the sex organs, and were then passed on to offspring. The strongest argument for this theory was simply that he couldn’t think of anything better. “It is a very rash and crude hypothesis,” he wrote to his friend T. H. Huxley, “yet it has been a considerable relief to my mind, and I can hang on it a good many groups of facts.”2

  He never came up with a better explanation, although the key to the truth was literally under his own roof.

  At Darwin’s death in 1882, his library contained unopened copies of a short paper in German by the Austrian botanist (and Augustinian friar) Gregor Mendel, which Mendel had presented in 1865 to his local natural-history society. The paper recounted Mendel’s nine years of experimenting with hybridization; he had tried to create a new species by interbreeding thirty-four different varieties of sweet peas, and although he had failed, he had discovered a series of laws that seemed to govern how the characteristics of the sweet peas (shape and color of seeds and pods, position of flowers, length of stem) were passed on.3

  These laws, Mendel noted, operated with “striking regularity.” Some of the characteristics of the peas were always passed on to the next generation, “entire, or almost unchanged”; he called these “dominant” characteristics. Other aspects seemed to disappear in the offspring but then would sometimes reappear unchanged several generations on; these, which became latent, Mendel termed “recessive.”

  The painstaking cross-fertilization of generation after generation of sweet peas allowed Mendel to work out a series of formulas for the passing on of these dominant and recessive characteristics. Clearly, the characteristics were carried from parent pea to offspring pea by the egg and pollen cells, so (Mendel proposed) those cells must contain discrete units, or elements, with each element carrying a particular characteristic within it: “The differentiating characters of two plants,” he concluded, “can finally . . . only depend upon differences in the composition and grouping of the elements which exist in the foundation-cells.” The proper manipulation of those elements could change the characteristics of the next generation—and, eventually, even mutate one species into another.

  If a species A is to be transformed into a species B, both must be united by fertilisation and the resulting hybrids then be fertilised with the pollen of B; then, out of the various offspring resulting, that form would be selected which stood in nearest relation to B and once more be fertilised with B pollen, and so continuously until finally a form is arrived at which is like B and constant in its progeny. By this process the species A would change into the species B.4

  This was the answer to Darwin’s vexing problem, the mechanism by which a variation could pass from one generation to the next and ultimately shape a species into something else.

  But a cascading series of events prevented Mendel from developing his research further. He was, first and foremost, a friar rather than a scientist, so he did not push for the translation and distribution of his paper; it was known, mostly, to the forty people who had bothered to turn up in 1865 to hear him read it. The one prominent scientist who did take notice of it, the Swiss botanist Karl Wilhelm von Nägeli, was a die-hard proponent of blended inheritance and sharply criticized Mendel’s results. Nägeli insisted that Mendel redo all of the experiments using hawkweed, but this venture failed horribly because hawkweed does not need to be pollinated in order to produce seeds (meaning that none of the resulting seeds were actually hybrids). And in 1868, Mendel’s monastery elected him abbot for life; this not only pulled him away from his experiments but got him embroiled in a complicated, time-consuming argument with the Austrian government over the amount of tax the monastery paid.

  Still, Mendel continued to think of himself as a naturalist; he went on experimenting with breeding and hybridization of flowers, fruit trees, and honeybees, and he became known, over the next decade, for his meteorological observations and theories. “My scientific work has brought me a great deal of satisfaction,” he told a colleague in 1883, the year before his death, “and I am convinced that it will be appreciated before long by the whole world.”5

  He probably wasn’t thinking about the sweet-pea research, which had been eclipsed by his other concerns; but the sweet peas were what the world remembered.

  •

  Just one year after Mendel’s paper was published, the German biologist Ernst Haeckel proposed that inheritance might be controlled by something deep inside the core of the cell. He didn’t have either the equipment or data to prove this theory, but two decades later, his countryman Walther Flemming made use of much-improved microscopic lenses and better staining techniques to observe minuscule, threadlike structures in cells that had begun to divide (mitosis). Flemming’s colleague Wilhelm Waldeyer suggested that these should be called chromosomes, a name that simply described their ability to soak up dye (chroma, “color”; soma, “body”).6

  And then the sweet peas resurfaced.

  On May 8, 1900, the botanist William Bateson, was on his way to deliver a talk about the difficulties of heredity to the Royal Horticultural Society of England. He had brought a sheaf of research articles to read on the train; Mendel’s German paper was among them. By coincidence, Bateson’s hand lighted on Mendel’s work first; halfway through, he realized that the formulas were the key to the problem of inheritance. (Possibly he had read the paper earlier, but the train story is the one he always told afterward; it had more dramatic flair.)

  Coincidentally, two other researchers had also recently come across Mendel’s work: the Dutch botanist Hugo de Vries, who had been conducting his own experiments with hybridization; and a student of Nägeli’s, Carl Correns. Within the year, all three men published papers dealing with problems of heredity and citing Mendel’s “laws” of inheritance. In 1901 the Royal Horticultural Society sponsored the first translation of the German study into English, bringing Mendel’s laws fully into the public gaze.7

  All that remained was to connect the chromosomes with the laws.

  In 1902 the German biologist Theodor Boveri carried out a series of experiments demonstrating that sea urchin embryos needed exactly thirty-six chromosomes to develop normally—which strongly suggested that each chromosome carried a unique and necessary piece of information. Simultaneously, American graduate student Walter Sutton, working at Columbia University, concluded from his experiments with grasshoppers that chromosomes carry the “physical basis of a certain definite set of qualities.” Not Darwin’s gemmules, or Mendel’s elements: genes, carriers of information from one generation to the next.8

  The term was coinvented by William Bateson, who first called the new study of chromosomes and their relationship to inheritance genetics, and the Danish botanist Wilhelm Johannsen, who separated out the word gene and applied it to the unit of heredity itself. Forty years after Mendel first published his experiments, twenty years after his death, he created a whole new field within biology.

  As he had predicted, the whole world finally appreciated his work.

  GREGOR MENDEL

  Experiments in Plant Hybridisation

  (1865)

  Mendel’s paper was translated into English by the Royal Horticultural Society of London in 1901; this clear and succinct translati
on remains the standard. W. P. Bateson’s republication of the entire English-language paper in his 1909 book Mendel’s Principles of Heredity is widely available online; Cosimo has also republished it in a high-quality paperback with all formulas and diagrams included.

  Gregor Mendel, Experiments in Plant Hybridisation, Cosimo Publications (e-book and paperback, 2008, ISBN 978-1605202570).

  TWENTY-TWO

  Synthesis

  Bringing cell-level discoveries and the grand story of evolution together

  Biology at the present time has embarked upon a period of

  synthesis after a period in which new disciplines were taken

  up in turn and worked out in comparative isolation. . . .

  Already we are seeing the first-fruits in the re-animation of

  Darwinism.

  —Julian Huxley, Evolution: The Modern Synthesis, 1942

  World War I was over, and Charles Darwin was in trouble.

  These were not unrelated phenomena. “The one event . . . which more than any other single one laid the foundation for the situation in which Western Europe finds itself today,” the American biologist Raymond Pearl remarked, just before the armistice of 1918, “was the publication of a book called The Origin of Species.” He was voicing a widespread opinion: Darwinian natural selection, by removing the human race from its special position as a purposeful and unique creation of God, had plunged humanity into the same grim, amoral struggle for survival that the rest of the animal kingdom endured. “All nature is at war,” Darwin himself had written. It was no wonder that this war had engulfed Homo sapiens too; no wonder, Pearl wrote (in an eerily prescient phrase), that the Germans had ruthlessly undertaken the “biological elimination” of another nation.1