The Triumph of Seeds (20 page)

In the weeks I spent baiting traps below the Raccoon Shack, I found myself wishing that rats had never evolved. But even in a world without rodents, something probably would have been after my peas. Once mother plants began packing lunches for their babies, everything from dinosaurs to fungi wanted a taste, and the evolution of seed defenses became inevitable. The relationships sometimes find a balance, but not always.
Almendro
trees appear to have the rodent situation figured out, but they must not have planned for peccaries, aggressive wild pigs whose massive molars can split and crush the seeds with ease. Even worse, the Great Green Macaw specializes on
almendro
, nesting in the trees and gorging on the seeds, which it can handily crack with a bill specifically adapted to the purpose. Among seed predators, birds have one of the longest evolutionary histories. They descend from dinosaurs, some of whom developed seed-crushing organs over 160 million years ago. Paleontologists know this from fossils containing telltale clusters of
gastroliths
, the distinctive little stones found inside gizzards. Modern birds still depend on grit to grind their food, and the strongest gizzards occur in seed-eaters—everything from chickens to canaries, grosbeaks, jays, and perhaps the most famous group of birds in the world.

F
IGURE
8.3.  The larderhoard of a Norway rat family underneath the Raccoon Shack, final resting place for most of the pea harvest from my Mendel experiment. P
HOTO
© 2013
BY
T
HOR
H
ANSON
.

F
IGURE
8.4.  This classic illustration by John Gould shows some of the diversity of beak shapes in Darwin’s Galapagos finches. Charles Darwin,
Journal of the Beagle
(1839). W
IKIMEDIA
C
OMMONS
.

For Charles Darwin, the finches of the Galapagos Islands appeared like a gaggle of unrelated species, more notable for their tameness than anything else. As he recorded in the field, “Little birds . . . will alight on your person & drink water out of a basin held in your hand.” It wasn’t until his specimens reached ornithologist John Gould, who had worked on parrots and was very familiar with seed-cracking bills, that their close affinity came to light. As famously told in Jonathan Weiner’s
Beak of the Finch
, biologists have since learned that seasonal changes in seed abundance produce measurable evolutionary
changes in the finches. Differences of
less than half a millimeter in bill length determine which birds can crack the toughest seeds and which can’t. In times of scarcity, that distinction is a matter of life and death, and as a result, the bills of whole populations can change
in a single generation
. The fact that natural selection can play out so quickly helps to explain how one original Galapagos finch could have morphed into thirteen species, some with seed-crushing bills, some that sip nectar, and some that eat fruit or insects. There are also cactus-flower probers, and a finch whose beak can hammer bark like a woodpecker. Played out globally, the Galapagos scenario helps the mind grasp how specializing on seeds (or other foods) can have such evolutionary influence. According to one theory, overcoming the physical challenge of eating hard-shelled seeds may have even produced the distinctive shape of the human skull.

As a child, I subjected my skull to a typical variety of sports. Though I eventually settled on swimming, I passed several seasons playing soccer and baseball, and even briefly threw my small frame into the melee of American football. One similarity among all these activities was the healthful snack served during practices and games: fresh oranges sliced into wedges. And, given that snack, we young athletes would immediately stuff wedges into our mouths, skin side out, and run around hooting like chimpanzees. Try this now and you’ll find that it does create an undeniably ape-like impression. But it’s not the wide orange smile that does it. I spent two years studying mountain gorillas in Uganda, and while they expressed themselves in all sorts of ways, I rarely saw them leer. The orange-wedge trick works because it reshapes the skull, giving a forward, snout-like projection to the jawbone. All other apes, and most ancient hominids, share that structure. But in human ancestors, the face began to flatten, and that’s where the seeds come in.

“There was a radical shift around 4 million years ago,” explained David Strait, a professor of anthropology at the State University of New York. Modern human faces appear flat because our bones are small, he told me, probably an adaptation for eating soft, cooked
foods. But it was another dietary shift that started the ball rolling. “The facial reinforcements,” he said, “the large cheekbones and muscle attachments, the size and shape of the teeth—all point toward producing and withstanding high loads.” Just the kind of “high loads” that come from cracking the shells of hard seeds and nuts.

For much of the past decade, Strait and his team have argued that habitually biting large, hard objects like nuts explains the changes in ancient skulls. Their computer models show the digitized facial bones of
Australopithecus
—an extinct hominid best known for the “Lucy” specimen—happily munching away, with the force of each bite distributed particularly above certain teeth. It’s a habit we maintain. To revisit the sports analogy, spectators at a game don’t eat orange wedges. Instead, they litter the stands with hot dog wrappers, drink cups, and, invariably, the empty shells of dry roasted peanuts. Next time you have a bag, notice which teeth you use to crack open the tough ones. Chances are you’ll position that nut on the side of your mouth, right behind the canines, where your skull best absorbs the force of the bite. Those are the premolars, and if Strait is right, using them for nutshells is a deep, evolutionary instinct.

“A lot of my colleagues don’t believe me,” he laughed, “and that’s fine!” Critics of Strait’s “hard-food” theory point to chemical analyses and patterns of tooth wear that suggest a diet dominated by grasses or sedges. But Strait doesn’t see this as a conflict. Ancient hominids might have gobbled up all sorts of things when food was abundant, but just like the Galapagos finches, what really mattered was getting through the tough times. “Nuts were the fallback food,” he said, and fallback foods can drive evolution because the stakes are so high. “Soft foods and fruits are wonderful and sweet,” he told me, with the ease of someone practiced at making his point, “but when those run out, you either have to move, eat something else, or die.” In those terms, it makes perfect sense for the hominid face to reorganize itself around a nut-chomping, premolar bite.

If the habit of eating hard seeds did influence our skulls, much in the same way it shaped finch beaks and rodent jaws, then how might
human chewing have impacted seeds? Toward the end of our conversation, Strait hinted at an answer. He mentioned new research showing how the micro-structure of seed shells mirrors that of tooth enamel. In each case, the cells lie in tight rows of ray-like rods and fibers, as if both sides arrived at the same engineering solution to resist the impact of the other. He also passed along a paper about a Southeast Asian seed so strong it can barely germinate—the halves of its dense husk cling together at the very limit of what a growing shoot can split apart. Yet in spite of this, the seed still falls prey to beetles, squirrels, and the occasional orangutan. It’s a reminder that physical defenses can only go so far. From
almendros
to peanuts, the story is the same: no matter how strong a seed’s shell, there will always be a rat, parrot, or sports fan nearby who evolves a way to break through. Which is, of course, why shells are only the tip of the iceberg. If plants could successfully protect their babies just by building a better box, then there would be no point in drinking coffee, Tabasco sauce would be tasteless, and Christopher Columbus would never have sailed for America.

CHAPTER NINE

The Riches of Taste

All hot! All hot!

Pepper pot! Pepper pot!

Makes backs strong
,

Makes lives long
,

All hot! Pepper pot!

—Traditional Philadelphia street-vendor cry

“Y
ou come from far away,” the old man said, “where the devil left his jacket.” His speckled grey pony shifted beneath him, shaking the braided circlets of blue, red, and green leather that hung from its homespun bridle. I tried to meet the man’s eyes, but his stare never wavered from the air just above our heads. So I smiled at the horse, feeling foolish. They were blocking our path, but as visitors to a tribal area we needed permission to pass. The conversation didn’t seem to be going well.

“We’ve been mistreated ever since you came here,” he said, and I was confused. Hadn’t we just arrived? I wasn’t even sure if
almendro
grew in this forest. Then he clarified: “You and your Columbus.”

In biology, scouting new research sites occasionally involves sneaking a look at a promising field or forest without leave. But those few words reminded me that I was trespassing on an entire continent.
Even the Costa Ricans with me didn’t count as locals—their ancestors came from Spain, following the trail blazed by Columbus himself when he dropped anchor at nearby Puerto Limón in 1502. Eventually, the old man nudged his pony to the side of the road and, having made his point, graciously gave us welcome. We didn’t find
almendro
that day and I never returned, but his words stayed with me. Centuries may have passed, but people still journey to the ends of the earth searching and seeking. And later I realized that Christopher Columbus and I did have one thing very much in common: we’d both come looking for seeds.

“Simply standing on the beaches,” the great explorer once wrote, “ . . . we find such traces and clues of spices that we have reason to believe much more will be found in time.” The logbook from his first voyage contains no fewer than 250 botanical descriptions, often-detailed accounts of the crops, trees, fruits, and flowers he encountered in the Caribbean. But while the list included plants (and seeds) that would redefine European cuisine and commerce, from corn to peanuts to tobacco, Columbus showed hints of disappointment as those first weeks wore on. “I am sorry to say I do not recognize them,” he wrote, after inspecting the herbs and shrubs of Isabella Island (now Crooked Island). Several days later, the flora made him “extremely sorry,” and in another passage he laments a forest of fragrant but unfamiliar trees: “It grieves me extremely that I cannot identify them.” Columbus felt worried, because while his ships may have bumped into a New World along the way, the admiral had promised his sponsors a much different outcome. Queen Isabella, King Ferdinand, and all of his other noble backers expected more than tales of discovery—they wanted to get rich. They had invested in a new trade route to Asia and expected a return paid in Asian products: gold, pearls, silk, and, above all else, the exotic spices that grew nowhere else. Unfortunately, neither Columbus nor anyone traveling with him had any idea what they looked like.