American Buffalo (4 page)

The bulk of buffalo history is set in the geologic epoch known as the Pleistocene, which spanned from about two million years ago to ten thousand years ago. Of the geologic epochs, the Pleistocene is by far my favorite. Its relationship to the modern world reminds me of my own relationship to my grandparents: their lives were distant and obscure enough that it’s difficult for me to really know and understand them, but what I do know about them helps explain a lot about how I turned into the kind of person I am.

However, whether or not bison history actually began in the Pleistocene depends on how you define “began.” If we think in terms of life beginning at conception rather than at birth, we might say that the bison “began” during the epoch that preceded the Pleistocene, called the Pliocene. During the Pliocene, it must have felt as if the gods had turned on an air conditioner and a dehumidifier—imagine a hot and swampy earth cooled off and dried out. Savannas and grasslands had spread across most continents, giving rise to a great diversification of long-legged grazing mammals. One of these mammals was a now-extinct critter known as the Proleptobos, which appears in the fossil record of Asia at about four million years ago. By the end of the Pliocene, the Proleptobos had split into two different groups, cattle and bison. The bison at that time were small and slightly built, and they were soon to enjoy a great expansion of their range; during the early Pleistocene, they spread across most of Eurasia.

The earth more or less continued to cool off during the Pleistocene, which is known somewhat generally as the Ice Age. Really, it’s more accurate to say that the Pleistocene epoch contained many ice ages. There were at least seventeen glacial episodes during the epoch’s two-million-year span. The episodes varied in terms of severity, but each one followed a cycle that lasted about a hundred thousand years. Each cycle was marked by a glacial period, when ice sheets expanded and climaxed, and an interglacial period, when ice sheets receded. Sometimes the changes were extremely rapid, occurring in just a matter of decades. During the interglacial periods, global temperature averages were as warm as or warmer than today.

Some geologists refer to the most recent glacial episode as the Wisconsinan. It peaked about twenty thousand years ago, and it was a doozy. Glacial ice covered much of the Northern Hemisphere; the Great Lakes region of the United States was under one and a half miles of ice.
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With so much of the earth’s water tied up in glaciers, ocean levels were much lower. This caused a phenomenon of tremendous ecological significance: dryland corridors formed between landmasses usually separated by immense bodies of water.

There were many such corridors that opened between various landmasses during the Pleistocene, but for our topic here—the advent of the American buffalo—one of them is particularly important: the Bering Land Bridge. When I was a kid, the Bering Land Bridge always baffled me. I pictured it as a long, narrow hallway running between two continents, with walls of ice and water mounded up on the sides. When I heard about animals and man crossing it, I imagined them making a mad dash, like Moses crossing the parted Red Sea. Actually, though, that is not a good way of looking at it. Instead of picturing a “bridge” connecting Siberia and Alaska during times of lower ocean levels, one should imagine them as being connected by a landmass. That landmass has a name—Beringia—and it was huge. Basically, the entire western border of present-day Alaska stretched out to join the entire eastern border of present-day Siberia. That’s one thousand miles from north to south, or about the distance between Miami and New York City. Beringia was dominated by rolling hills, grasslands, and broad valleys. It did not get much snow and was free from glaciers. The dire wolf fed on horses where king crabs now feed on clams.

Several times during the Pleistocene, the dryland corridor of Beringia was open long enough to allow a nearly complete homogenization of wildlife between Siberia and Alaska. That is, animals were able to move freely back and forth between the continents. Of course, these migrating animals would probably have had no idea that they were “going” anywhere. They were just moving along, heading where there was food and a more suitable climate. Individual animals would have been born and would have died on land that is now underwater, and it may have taken several generations for a population of animals to actually “cross” the land bridge.

While there was some interchange going from North America to Siberia, such as the horse, the predominance of faunal exchanges went in the other direction, from Siberia to North America. It seems that the first of several bison migrations happened during the second-to-last glacial episode, about 140,000 years ago. Scientists often refer to these early arrivals as Eurasian steppe bison (
Bison priscus
). In the cave art of Paleolithic European hunters, the steppe bison is often portrayed with curvaceous horns, a large shoulder hump, and a mane so thick that it almost appears to be a second hump. The steppe bison shared the North American landscape with a host of bizarre and fascinating animals that I wish were still around: flat-headed peccaries and beavers that were the size of modern pigs; an armadillo the size of a black bear; the ox-sized Jefferson’s ground sloth, which had lips capable of gripping things; the twenty-foot-long, elephant-sized Rusconi’s ground sloth, which dragged itself along on its knuckles and used its tail as a support when it stood up to feed on leaves; the one-ton giant short-faced bear, which had catlike teeth and a skull that was almost as wide as it was long; as many as six different camels, including one that was seven feet tall at the shoulder; two horses, including one that may have been striped like a zebra; several elephants, including the five-ton Columbian mammoth, the ten-ton woolly mammoth, and the forest-dwelling American mastodon; and also an impressive array of large cats, including the 275-pound dirk-toothed cat, the 400-pound Ice Age jaguar, the 600-pound scimitar cat, the 700-pound saber-toothed cat, the 850-pound American lion, and two American cheetahs of indeterminate size.

The steppe bison thrived alongside many of these mammals on the semi-arid grasslands of eastern Beringia, where it was confined by the same factors that had allowed for its arrival. That is, the glaciers that caused the ocean levels to drop also served to block the animal’s southward migration into what is now the Lower 48 of the United States, or the mid-continent.

Eventually, during the interglacial period that separated the last two glacial periods, a north-south corridor opened through western Canada. Bison passed through the corridor maybe a hundred thousand years ago, emerging on the Great Plains near the location of Edmonton, Alberta. During the next and final glacial period, the Wisconsinan, that corridor was closed again by advancing glaciers. The bison in the south would never again interbreed with those in the north, and they would each follow their own evolutionary paths: the northern path led to extinction, the southern to the American buffalo.

Populations of animals that are colonizing new territory sometimes undergo sudden and dramatic evolutionary changes. There are a couple of reasons for this. First, the colonizing population is likely to be numerically small and may contain only a fraction of the original population’s genetic diversity. Thus, the new founder population can turn out to be slightly different from the parent population, and there’s less genetic anchoring, or genetic stability, to “pull” the founder population back into line. When it comes to colonizing postglacial territory, the new population is also likely to have abundant access to food and a low population density. The Russian-born zoologist Valerius Geist has linked these conditions to the phenomenon of “giantism” in ungulates such as buffalo. The animals develop what Geist describes as “altered body proportions” and “huge and often bizarre horns.”

That’s what happened to
Bison priscus
; the animal experienced an evolutionary growth spurt and turned into the monster-horned
Bison latifrons.
It was one and a half times as big as the modern form of the animal, with horns as long as an NBA player. That relatively quick move toward giantism, however, was followed by a much longer movement in the opposite direction. For whatever reason, the large horns and body size of
B. latifrons
became disadvantageous to the animal. Perhaps
B. latifrons
’s predators learned to exploit the animal’s ungainly size, and quicker, more agile animals were more likely to survive. Or perhaps a reduction in the available food supply, or greater competition for that food, gave an advantage to animals with smaller body sizes. The evolutionary trend toward smallness, or diminution, continued for thousands of years. By around twenty thousand years ago, the long, straight horns of
B. latifrons
had given way to the shorter, curved horns of
B. antiquus.
The animal continued to get smaller, and by about five thousand years ago it had assumed the basic shape and size and behavioral characteristics of the buffalo that we know today,
Bison bison.

Of course, the buffalo is still changing—maybe more rapidly now than at any other time. We may not know until much later, maybe thousands of years from now, when we have a distant point of perspective from which to look at it.

I often wondered how my own buffalo skull fit into the grand scheme of the animal’s history. Was it actually what I’d been calling it, an American buffalo, or was it from one of those remnant forms of the past? I worried that perhaps it belonged in a museum, or maybe had some value to science. I studied a system of bison skull diagnostics known as “cranial characteristics and horn-core morphology”; you take a bunch of measurements of a buffalo skull, with particular focus on the horns, and those measurements help you extrapolate what sort of skull you’re looking at. I got my hands on a list of twenty-six of those measurements and felt like I was holding a secret code that would unravel a great mystery. However, the measurement descriptions were somewhat puzzling; I was supposed to measure the “rostral width at maxillary-premaxillary suture,” the “transverse diameter of core at right angles to longitudinal axis,” and the “width of skull at masateric process above M1.” Not only did I not know what any of those parts were, but I felt that the measurements were callously indifferent to the reality of my skull’s condition: it wasn’t all there, and much of what was there was crumbled and chipped.

My next attempt at identifying the skull brought me all the way to Oxford University, in England. I had read an academic article titled “Rise and Fall of the Beringian Steppe Bison,” which appeared in a 2004 issue of the journal
Science.
The article provides a timetable supporting a claim that the bison began sliding toward extinction across the northern extent of its range about thirty-five thousand years ago. The article’s primary author is Beth Shapiro, a leading expert on ancient DNA who works at Oxford University. In researching the article, Beth and her colleagues had extracted genetic material from the skeletal remains of around five hundred bison that lived in Alaska and northern Canada thousands of years ago. Ancient DNA tends to be highly degraded and eroded—it would be virtually impossible to use it for cloning—though it can be used to reveal the effective population size of a breeding group, as well as how the particular animal fits into the overall evolutionary history of its species. I called Beth Shapiro one day, introduced myself, and asked if she could work some of her magic on my buffalo skull. She told me she’d be happy to try.

It was wintertime when I arrived in Oxford. The snowfall was so light that the flakes looked like drifting campfire ash. Underdressed students hustled from building to building with their chins tucked into their collars and their hands pulled up into their sleeves. I walked to the Henry Wellcome Ancient Biomolecules Centre and waited outside for Beth Shapiro.

Beth arrived on a bicycle. She mentioned that she was suffering from a mild hangover as she fiddled with her belly button ring, which seemed to have snagged itself on an article of her clothing. Beth grew up in Rome, Georgia, where she landed a job in tenth grade as the news anchor on her local television station. She’d go to work at 6:00 a.m., do the news, and then get to school during the second hour. After school, she’d go back to the television station and work until 6:00 p.m. After graduating from high school with honors, she got a university degree in ecology in 1999 and then landed a Rhodes scholarship to study evolutionary biology at Oxford. She’s been there long enough to pick up a touch of an accent, and she’s fond of words such as “bloody” and “rubbish.”

Beth led me around to the back of the biomolecules center. No one is allowed to use the front door because they’ve found that genetic contaminants have a way of coming in off the street. Beth told me several stories of people who’d made “great” discoveries with ancient DNA only to find that they hadn’t: a genetic researcher looking for DNA from an extinct saber-toothed cat found some feline DNA all right, but it turned out to come from someone’s house cat.

Another time, a team of researchers working in England claimed to extract from salt crystals a form of bacterial DNA that was tens of millions of years old. Until then, the oldest successfully extracted samples of DNA came from organisms that were only forty to eighty thousand years old. “We got their data and looked at it and said, ‘Piss off,’ ” Beth told me. “We later got the same DNA from dirt that I collected on the roof of Oxford University’s Museum of Natural History. So either that roof has bacterial DNA that’s associated with salt crystals that are a hundred million years old, or they were dealing with a contaminant.”

To avoid such contaminants, we stripped out of our outer clothes and stepped into one-piece white lab outfits with rubber bootees, latex gloves, skintight hoods, and full face masks. We looked like we were going to clean up a chemical spill. Then we stepped through a series of doors, closing each set behind us before opening the next. We arrived in a room that was piled here and there with sealed plastic bags containing some alarming labels. There were several bags of “unused plague samples.” There were samples of thirty-five-thousand-year-old giant ground sloth shit, taken from a cave in South America. (“Poop’s great,” said Beth. “You can get the animal’s own DNA, and also the DNA from its intestinal parasites.”) There were mammoth bones, bones from extinct horses, saber-toothed cat bones, and short-faced bear bones. Beth opened a freezer to show me two complete human skeletons. “Dead Victorians,” she said. “Some archaeologists turned them up. No markings on the graves. I’m trying to give them away because they’re taking up space. I’ve offered to throw in this bloody freezer to whoever will come and get them.”