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  One of the examples of the seemingly perfect match between plants and animals in their environments was that some plants have seeds with hooks that are useful because they snag onto the wool and fur of mammals to be carried to fertile soils. Yet Darwin knew that some such plants and seeds are also found on islands where there are no furry mammals.34 It hardly made sense in the theory of independent creations, but it made sense given the notion that seeds simply arrive at places by natural transport.

  Such transport did not seem random because it followed definite oceanic currents. He also knew that the average speed of Atlantic currents was about thirty-three miles per day (some as high as sixty miles per day), and so he estimated that seeds might travel nine hundred miles in open ocean in a month. After similarly considering how the eggs of certain animals travel, Darwin's findings converged on this conclusion: life on the Galápagos was not created there, it arrived by natural processes.35

  So organisms thus spread to environments to which they initially were not perfectly suited, and there they changed. But how? Being acquainted with the theory of Lamarck, Darwin believed, wrongly, that as individual organisms change their habits in response to their environments, they acquire traits that are subsequently inherited by their offspring. Still, this mechanism seemed insufficient to explain the great complexity of many species.

  Elsewhere, back in 1755, worrisome observations about population growth had been published by an anonymous author in Pennsylvania. He had analyzed demographic data on births, deaths, and marriages, and he concluded that owing to America's extensive resources and land, population there would continue to grow nearly unchecked, to thus double at least every twenty or twenty-five years. America seemed destined to eventually have more Englishmen than Great Britain, and someday, even all the land in America would not be enough to sustain the population. The article was widely reprinted, even in a book on electricity. The anonymous author was a printer and civic activist in Philadelphia: Benjamin Franklin.36 He further argued that Englishmen should therefore seize Canada for the sake of the future.37 This finding, that human populations growing unchecked would increase exponentially, became an issue of political concern.

  In 1798, another anonymous author, in London, also published his concerns about population expansion. He included his name in the subsequent editions of his essay, it was Reverend Thomas Malthus, an Anglican clergyman who became a prominent political economist. In late September and October of 1838, Darwin was reading the 1826 edition of Malthus's Essay on the Principle of Population.38 Malthus had argued that because the sexual attraction among people is so strong, populations have a gross tendency to expand. In principle, the rate of expansion would be geometrical (he noted that in the United States the population had continued to double every twenty-five years), but expansion was limited by lack of resources to feed everyone, given a limited terrain. For Malthus, poverty and starvation were not results of the unfair distribution of wealth, they were natural and nearly inevitable. Although he earned the contempt of optimistic social reformers who claimed that society could flourish by redistributing wealth, Malthus contended that redistribution (as when the wealthy tried to help the poor) usually failed because people continued to breed too much, again creating poverty and starvation.39 Wars would ensue unless people exercised moral restraint to avoid giving birth to children they could not feed. Malthus believed that God allowed such apparently harsh conditions so that people would strive for a moral purpose. Misery, starvation, and war could teach humans the virtues of labor and moral behavior. He explained that population expansion exerts constant pressure against the local means of sustenance, thus acting to drive people to migrate to inhospitable lands, to invade peaceful countries, and to fight against other restless tribes like barbarians in a “perpetual struggle for room and food.” He wrote: “And the frequent contests with tribes in the same circumstances with themselves, would be so many struggles for existence, and would be fought with a desperate courage, inspired by the reflection, that death would be the punishment of defeat, and life the prize of victory.”40

  As Darwin read Malthus, he realized that such struggles for existence happen among animals, too. Lacking morals, animal populations expand until there are not enough resources to support them all. Darwin reasoned that animal populations could “increase at a geometrical ratio FAR SHORTER than 25 years,” and hence, that species compete for resources, and individuals compete against one another.41 Those less suited to obtain enough food and comforts die. Darwin realized that this pressure would effectively change a species by favoring particular traits.

  But could it be, really, that species just were not in perpetual balance with their environments? Again, Darwin tested his conjectures, partly with experiments. In one plot of soil he planted native English weeds, from which there germinated 357 seedlings, and he found that, soon, 295 of them were killed, mainly by insects. He also found that in a small section of turf subject to mowing or grazing, 9 out of 20 species of plants perished; the more vigorous ones survived. Such experiments, plus many observations in the wild, led Darwin to conclude that plants and animals compete constantly against one another to survive. Plus, the climate affected all living things, chiefly by reducing the food supply. Darwin noted, for example, that just one winter season killed about four-fifths of all the birds on his grounds. Observing nature, he found that there are tremendous rates of death.

  When we briefly walk in the woods, nature seems harmonious. But all beings, Darwin reasoned, are subject to severe competition. Some trees scatter thousands of seeds to subsist, as organisms feed on one another. He estimated that just one pair of elephants, apparently being the slowest breeding animals (by birthing only about six offspring in ninety years), would produce fifteen million living descendants in just five centuries.42 How many more would they produce in a thousand years or more? The absence of any such huge population of elephants showed that an immense number of offspring perish continuously. Darwin wrote: “The face of nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force.”43 And he realized that the struggle is greatest among members of the same species, especially among siblings; the young suffer most.

  All offspring exhibit certain variations compared to their parents. Some of those variations are advantageous whenever there are hazards or a lack of resources. Thus, individuals having even slight advantages tend to survive in greater numbers and thus to reproduce and transmit such traits in greater proportion. Over time, the population changes as disadvantageous traits diminish. Thus Darwin realized that nature affects species analogously to how breeders make “pure” varieties of pigeons, dogs, and cattle. By selecting which individuals mate, breeders or nature shape future animals. The continued selection of specific traits in an isolated population gives it a distinctive look. And if no barriers prevent intermixing among populations, there arise new mongrel varieties. Darwin carried out experiments that showed that, indeed, distinct types of plants mix with their neighbors; they do not keep their “purity” in the wild. The environment determines whether species evolve or become extinct. Darwin called this process natural selection: how environments shape species. He expected that it proceeds very gradually, requiring no sudden large changes, no major catastrophes. Species change would be retarded by intercrossing, but it would also be facilitated in places where populations are isolated for immense periods of time.

  Thus, Darwin changed his mind. He had believed that species appear by miracles in their native lands, perfectly suited to live in constant harmony with the environment. But many species had ceased to exist, just as landscapes and climates had changed. Lacking permanent balance, nature is in flux, and some species survive in environments where they don't comfortably fit. Animals and plants struggle, and through that process, Darwin thought, many populations gradually evolved and adapted exquisitely to their dynamic envir
onments.

  Such thinking seemed to suggest that species had not been instantly created by God. Or had God made this very mechanism so that populations adapt to changing conditions? Darwin dreaded religious controversies, so he kept his theory secret except to some close friends.

  In 1844, an anonymous book was published, arguing that species evolve by a progressive law of development.44 Scientists rejected it, but it became a bestseller and generated much controversy. Darwin continued to work on his own theory in relative secrecy. Fifteen years later, he published Origin of Species. But all that is another story.

  To return to the myth about finches, we can summarize that old story as follows: While visiting the Galápagos Islands, Charles Darwin noticed that various species of finches had beaks of different shapes and sizes. Observing their eating habits, he noticed that the shapes of their beaks corresponded to their diets. He also noticed that some species were distinct to some islands. Hence he inferred that the various species were related: they were descended from common ancestors that had populated the islands and had adapted variously to the distinct island conditions. Species evolved.

  This short story works because it fits in the space allotted by a science textbook. And it works because, as Sulloway argued, it fits into the form of a classic journey of discovery: man departs from home on a bold adventure, encounters and overcomes hardships, and returns with a deep truth. But the story is false, so the challenge is how to replace it with something better. Selecting elements from the longer account above, I suggest that we can well write: Halfway around the world, the young traveler Charles Darwin arrived at foreboding towering volcanoes, the “Enchanted Islands.” Their dark jagged terrain held swarms of hideous reptiles, “imps of darkness,” and tame birds. Yet Darwin found no frogs or toads on the islands. He found only the kinds of animals that could cross the salty waters from the continent. All resembled American species, but oddly distinct. He later concluded that such island species descended from colonists, but somehow evolved.

  The latter story is just as short as the old, just as appropriate for a textbook. And it's better, because it involves mythic imagery but is actually true.

  6

  Ben Franklin's Electric Kite

  LIKE Darwin's finches, other images have greatly influenced popular ideas about the history of science. One that is etched in our minds is that of stocky Benjamin Franklin flying a kite in a thunderstorm. It shows up in books, stamps, art, and currency, even on a U.S. silver dollar issued in 2006. It enchants because it shows a self-made American using a child's toy to make a major contribution to science: to prove that there is electricity in the clouds, that the awesome force of lightning involves the same stuff as electricity. But that image has lost some of its apparent certainty. Some commentators have faced a perplexing lack of evidence that Franklin ever conducted such an experiment.1

  The young Benjamin Franklin published and printed a newspaper called the Pennsylvania Gazette. Long before he investigated the nature of electricity, he published several reports about lightning. In 1731, Franklin reported: “From Newcastle we hear, that on Tuesday the 8th Instant, the Lightning fell upon a House within a few Miles of that Place, in which it killed 3 Dogs, struck several Persons deaf, and split a Woman's Nose in a surprizing Manner.” One year later, in 1732, Franklin described an incident in which a house in Allenstown “was struck by Lightning. It split part of the Chimney,” melted butter, and caused a fire.2 In 1736, Franklin's newspaper reported this bizarre anecdote:

  We hear from Virginia, that not long since a Flash of Lightning fell on a House there, and struck dead a Man who was standing at the Door. Upon examining the Body they found no Mark of Violence, but on his Breast an exact and perfect (tho' small) Representation of a Pine Tree which grew before the door, imprest or printed as it were in Miniature. This surprizing Fact is attested by a Gentleman lately come from thence, who was himself an Eye-witness of it; and ‘tis added that great Numbers of People came out of Curiosity, to view the Body before it was interr’d.3

  Franklin, the printer, actually believed the story—that lightning had imprinted the image of a tree on the man's chest.4 In 1742, another report appeared in his Gazette: “two labouring Men (standing under a Sawyers-Shead, on Society-Hill, to shelter themselves from the Rain) were struck down by a Flash of Lightning: But one of them recovering, found his Companion, Thomas Smith, dead; his Hat was much torn, and part of one of his Shoes torn off; on his Head, Neck, Breast, and the Inside of one of his Thighs were spots which appear'd as if burnt. The Survivor had most of the upper Leather of one of his Shoes torn away, and was burnt several Parts of his Body.”5

  Since ancient times, philosophers wondered about thunder and lightning. For example, Ovid claimed that Pythagoras knew the origin of lightning, whether it was caused by the god Jupiter, by storm winds, or by colliding clouds.6 Centuries of speculations transpired before scientists finally reached up toward the clouds and found electricity there. The story about Franklin using a long string to capture lightning from the sky resembles an ancient myth. In epic Greek poems, the god of sky and thunder, Zeus, hid fire from humans, yet Prometheus managed to steal it with the long stalk of a fennel plant.7 Prometheus stole fire from the god of thunder; Franklin caught “electric fire” from the thundering sky.

  If so, he was not the first. In May 1752, a few individuals at Marly-la-Ville, France, used a sharply pointed, forty-foot-tall iron bar to test whether storm clouds transmit electricity. As a cloud passed overhead, they extracted sparks of electric “fire” from the iron bar. This group, usually led by Thomas Dalibard (although he was absent during this first successful trial), was roughly following a proposed experiment by Franklin, although they worked independently.8 So Franklin himself was not the first to draw electricity from storm clouds. (Years later, in 1768, Franklin praised Dalibard by writing that Dalibard was “the first of Mankind that had the Courage to attempt drawing Lightning from the Clouds.”) Just a few months later, in July 1752, another French experimenter, Jacques de Romas wrote a letter to a scientific academy, stating that he planned to use “a child's toy” to explore the electrification of clouds.9

  On 27 August 1752, Benjamin Franklin's newspaper, the Pennsylvania Gazette, included a letter that summarized the lightning rod experiments of Dalibard and others.10 Franklin did not add the slightest note to the effect that he had carried out any comparable experiments. In October of that year, Franklin published in his newspaper a brief description of a kite experiment. In contrast to other experiments he had described, his account of this one was vague, and he did not specify when or where in Philadelphia it was carried out, he did not allude to any witnesses, and he did not actually state that he had conducted it.

  To clarify, Franklin did not describe what one might imagine: that lightning struck the kite to run electricity down the string—that would be deadly and the string would vaporize, as a bolt can have a temperature of 50,000° F, about five times hotter than the surface of the sun! Franklin wrote that during a thunderstorm, the experimenter should fly a kite bearing a metal spike, letting rain wet the twine to transmit electricity from a cloud, which would then charge a metal key attached to the twine before an insulating silk ribbon (kept dry because the experimenter should stand under a cover, holding the line out from a window or doorway). Then the experimenter could detect the “electric fire” on the key, using an instrument or his bare knuckle. Franklin wrote that the experiment is “easy”—that anyone could carry it out—but that just isn't so. The danger involved is so horrifying that few people dared to try anything of the sort. Besides, the difficulty of flying a kite out of a window during a rainy thunderstorm seems considerable. And details of Franklin's account seemed puzzling. For example, how long was the string?11

  Still, Franklin claimed: “the sameness of the electric matter with that of lightning completely demonstrated.”12 If so, why did he publish, just months later, a request asking readers of his newspaper to please send him any infor
mation about the effects of lightning “on Wood, Stone, Bricks, Glass, Metals, Animal Bodies, &c. and every other Circumstance that may tend to discover the Nature, and compleat History of that terrible Meteor”?13 Promptly after the account of 1752, a fellow scientist and friend wrote to Franklin that having read it, “I hope a more perfect and particular account of it will be published in a manner to preserve it better and give it more Credit than it can gain from a common News paper.”14

  The vagueness of Franklin's brief report is especially frustrating because if ever an experiment begged for detailed prescriptions, this is it. One does not play with lightning, a discharge that descends from about five miles (twenty-five thousand feet) in the sky, at a speed of about sixty thousand miles per second with heat and force that can split a tree, burn a house, melt an iron rod, and fuse silica sand into glass. As Tom Tucker has rightly commented, when we're merely reading we might not care much about details, but if you are going to actually try this experiment, then you are risking your life, and in that context, every word counts.