Natural History Magazine | Natural Selections

Bookshelf

February 2008

By Laurence A. Marschall

Animal Architects: Building and the Evolution of Intelligence,
by James L. Gould and Carol Grant Gould (Basic Books, 2007; $26.95)

Consider the steel and glass towers of Dubai or Singapore, the spare elegance of Frank Lloyd Wright’s Fallingwater, or the convoluted curves of Frank Gehry’s Guggenheim Museum in Bilbao, Spain. Consider even the most mundane big-box store, for that matter, and it is clear that we humans are master builders, able to create artificial environments orders of magnitude larger and far more elaborate than those of any other species on earth.

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Still, the architectural achievements of other creatures are nothing to sniff at, as the ecologist James Gould of Prince-ton University and the science writer Carol Grant Gould amply demonstrate in their stimulating study. Beavers, the most familiar animal builders, exhibit levels of engineering and organization that might challenge the Army Corps of Engineers. L.H. Morgan, an amateur naturalist who studied beaver dams near Lake Superior in the 1860s, described one that was 261 feet long, 6.5 feet high, and eighteen feet thick at its base. It was made up of tree trunks, limbs, branches, and stones, cemented together by vast amounts of mud and braced by sharpened stakes driven vertically into the ground. And if that sounds impressive, consider the mother of all recorded beaver dams, on Montana’s Jefferson River, which stretched nearly ten times farther—2,200 feet—from end to end.

If brain mass were correlated with architectural skill, one would expect most animal architects to be mammals. The truth is quite the reverse. Most mammals are content to sleep outdoors, use existing caves as dens, or at most, dig. The real masters of the building arts are birds and insects, whose nests and hives display an uncanny ingenuity in both design and creation.

Weaverbirds, for instance, natives to Africa, India, and Southeast Asia, not only weave, but seem to understand knots as well. Male weaverbirds begin construction by looping a thin strip of leaf or grass over a tree branch, then securing it by tying a knot. The bird suspends its nest from this secured strip, interweaving more strips of vegetation until it has stitched together a large ovoid dwelling, resembling a giant ball of twine. A narrow entrance discourages predators, and a comfortable nesting chamber opens up inside.

Tailorbirds, less industrious but even more resourceful, assemble arboreal hideaways out of leaves that hang adjacent to each other on branches. True to their name, they sew the leaves together with strands of spider silk. The birds even prepare the leaves by punching holes in both edges of each leaf and drawing them together with the silk until a snug hanging sack is formed. Once they fill the sack with moss and other soft plant materials, they have a comfortable and naturally camouflaged place to cradle their young.

The strangest and most wonderful animal structures, according to the Goulds, are the ones constructed not as nesting places, but rather for what amount to aesthetic reasons. Male bowerbirds, the crowlike creatures native to Australia and New Guinea, erect bizarre sculptures deep in the forest to appeal to the females, much as male peacocks display a fan of decorative feathers. The Vogelkop bowerbird, for instance, clears an area a yard or more across, then constructs a tower in the center of the clearing out of hundreds of small sticks. Depending on where he lives, he’ll build a thatched hut over his tower or leave it in the open. Finally, around the edge of the clearing, he assembles ornamental piles of contraband, such as colored stones, moss, and snail shells.

Do animal builders understand what they’re doing? Earlier investigators envisioned beavers, bees, and bowerbirds carrying out the steps of construction as if they were robots. But the studies cited by the Goulds reveal levels of social organization and conceptualization that can’t be explained that easily. How, for instance, to explain birds’ ability to repair damage to nests already under construction, or the weaverbird’s ability to create features on the inside of a structure that complement the ones on the outside. As with so many other traits that supposedly distinguish man from beast, architectural superiority turns out to be not a matter of kind, but only of degree.

Citrus: A History,
by Pierre Laszlo (The University of Chicago Press, 2007; $25.00)

Can one describe a work of nonfiction as being happy? Well, this one is. Pierre Laszlo, a retired chemistry professor turned science writer, has approached the lore of citrus fruit with the élan of a master chef (the man is French, after all), mixing history, economics, biology, and chemistry to produce a book that will bring a smile to readers of every taste. Until reading Citrus, in fact, I had not realized just how many tastes the title implied: lemon, lime, orange, and grapefruit, of course, but also citron, tangerine, kumquat, calamondin, and the self-descriptive Ugli, not to mention such variants as bergamot, mandarin, Valencia, ortanique, and Honey Murcott. Laszlo’s literary method is to present them as characters in an unfolding story. He begins with the domestication of the citron in Persia and the early history of citrus horticulture, then moves to the establishment and growth of the citrus industry in Florida, California, and Brazil, and finally, after many diversions and digressions, arrives at a final section that explores the place of citrus in literature, art, religion, and the culture of cuisine.

There are many surprises along the way. For instance, orange juice seems such a natural way to imbibe the fruit that it is difficult to imagine a breakfast without it. Yet until the 1920s, there were no efficient methods of bacterial disinfection, preservation, or distribution for such a perishable product. As a consequence, for those outside the citrus belt, fresh orange juice was a rare and expensive treat. According to Laszlo, it was an adman, Albert D. Lasker, who created the orange juice market almost single-handedly during a season when growers were saddled with a glut of excess fruit. At the time, new technologies had been developed that made it possible to pasteurize juice and transport it around the country far more efficiently. Lasker pounced: he launched a “Drink an Orange” campaign, which prompted the American public to adopt OJ as a tasty and healthy start to the day. The golden liquid got an added boost in the 1940s when growers learned to turn it into concentrate and flash-freeze it into compact cylinders. Open the freezing compartment in virtually any American refrigerator back in the 1950s and you’d find at least one can of Sunkist, Minute-Maid, or Tropicana.

Did you know that citrus peels are as ubiquitous in the modern household as the juicy fruit inside? The peels, it turns out, are filled with essential oils that can be turned into a wide variety of products. Limonene, for instance, found in most citrus peels, serves as the raw material for the molecular synthesis of many drugs. And since one variety of the limonene molecule invokes the sensation of oranges, while another variety is lemony, the two molecules are also used to impart flavor to a wide variety of soft drinks. It’s probably safe to say that, just as American breakfasts usually include orange juice, American lunches, at least of the fast-food variety, often include orange peel in the form of limonene-flavored soda.

Lest prospective readers worry that Laszlo has composed a paean to fast-food and industrial agriculture, note that he also includes a sampling of elegant citrus recipes that may induce readers to head for the kitchen. Among them is one for a wonderful Brazilian cocktail, the caïpirinha, another for sea bass with tangerine juice, and a third for an elegant tarte au citron. Good reading, good eating, and good humor make for happy reading. One might sum it up with a bon mot best resisted: If you love citrus, this is a book with appeal.

A Natural History of Time,
by Pascal Richet, translated by John Venerella (The University of Chicago Press, 2007; $29.00)

Looking at the sandy New England pond outside our summer house, I can readily imagine the glacial remnant that lay there some 12,000 years ago, melting in the warming rays of the Holocene sun. I know, too, that a few hundred million years ago, before continental drift split us apart, Europe and this bit of North American real estate were joined. And I’m well aware that 5 billion years ago, this sand and this water, indeed the Earth itself and everything on it, were part of an interstellar cloud that was condensing into our solar system. Deep time is just one of those things I take for granted.

But as geophysicist Pascal Richet demonstrates in this readable popular history of chronology, the geologic calendar implicit in today’s view of nature was not shared by earlier generations. Written accounts from ancient civilizations depict prehistory as a foggy dreamtime. Most authors made little attempt to assign dates or durations other than “in the beginning.”

To be sure, a few bold speculators such as Aristotle tried to attack the problem with pure logic. He asserted that the world was eternal, because it was impossible to imagine a beginning in which something arose from nothing. Nearly 2,000 years after Aristotle, Isaac Newton, the very emblem of the scientific revolution, used the new tools of astronomy to try to fit all of known history into a time frame beginning on page one of Genesis.

Only in the later 1700s did “natural philosophers” begin to learn how to read the dates nature has written in rocks. One of the most influential of those pioneers was the French polymath Georges-Louis Leclerc, Count of Buffon, who published his History and Theory of the Earth in 1749. Buffon devised a procedure that later investigators would find most fruitful: he measured or estimated the rates of natural processes that he was convinced had shaped the Earth, assumed those processes continued at a relatively steady pace, and thus calculated the time needed to transform the primordial Earth to its present state.

The best-known example of his method is a series of experiments he conducted on steel balls, from a half inch to six inches in diameter. Heating them to incandescence in a furnace, he measured how long they took to cool enough to be touched comfortably with the fingertips. Buffon knew from miners’ reports that the Earth’s internal temperature rises with increasing depth, and he interpreted this phenomenon to mean that the Earth was still cooling from a once-molten state. Extrapolating his results with small balls to a sphere the size of the Earth, he calculated the time it would have taken for the planet to cool to its present surface temperature: about 75,000 years. It was an audacious result—far longer than the biblical chronologies of a few millennia—but it carried the weight of experimental evidence.

Buffon’s cooling model, of course, was oversimplified, and his age for the Earth was a gross underestimate, but he was clearly on the right track. When later investigators determined the ages of mountains and canyons from erosion rates, or when they estimated the age of the oceans from their current salinity and the input rates of freshwater from inflowing rivers, they got periods longer than Buffon’s. But they were following his lead.

By the late nineteenth century, William Thomson, Lord Kelvin, had developed a refined version of Buffon’s cooling model and, with it, estimated 20 to 100 million years as the age of the Earth. Lord Kelvin’s was regarded as the most reliably determined value for the Earth’s age scarcely more than a century ago.

What Lord Kelvin and everyone else had neglected—because they knew nothing about it—was natural radioactivity. The interior of the Earth, it turns out, is heated by trace amounts of radium and uranium in its rocks, energy enough to keep the Earth warm for billions, not millions, of years. The discovery of radioactivity at the turn of the twentieth century not only raised the possibility of a much older Earth, but also made it possible to measure the ages of rocks. It was only necessary to determine the ratios of radioactive “parent” elements to their stable “daughter” elements in a rock.

Once radioactivity entered the picture, the pieces of the chronological puzzle all began to fall into place. Rocks from the Earth, meteorites, and moon rocks all yield ages of about 4.6 billion years. Strata bearing the scars of great geological events and the remnants of long extinct creatures have been mapped and dated. Only the fine details of the Earth’s timeline are matters of contention any more.

Yet precisely because the current well-grounded chronology seems so natural to most scientifically literate people, Richet’s authoritative review of Earth’s history is particularly welcome. Rather than fret about polls that show how many citizens still hold to the chronology of the Holy Book, he invites us to marvel at the efforts of science to read the book of nature itself.

Laurence A. Marschall, author of The Supernova Story, is W.K.T. Sahm Professor of Physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.