Why Did the Chicken Cross the World? (12 page)

Finding undisturbed and uncontaminated chicken bones that are centuries old is a remarkable feat. They typically don't last a day or
two in most traditional villages. Dogs, rats, and other animals quickly devour what little is left. Insects and soil can eat up what remains of that. Burney explains that if the ground is too acidic, bone degrades although seeds fossilize. If it is too alkaline, bones will turn to fossils but vegetation degrades. Here, the alkaline limestone and the acidic groundwater cancel each other out. “This is the Goldilocks zone, perfect pH, just right,” he says. “Which means both types are preserved. Basically, everything in here is preserved. It's like pages in a diary.”

We clamber back up into the hot sun, which has just risen above the lip of the cliff, cross into the shade, and watch a retiree in a white tennis hat sorting through the mud in a rectangular box with ­quarter-inch mesh. “Don't do every last little snail, but every bird bone and every seed we want to keep,” he tells her. “The biggest problem is that people try to screen too much at once,” he says, turning to me as she uses water from a garden hose to dissolve the mud. When she's done, we hose off the thick black mud that coats our legs to the knees.

Burney ships the chicken bones he finds to the southern Australian city of Adelaide. The five-thousand-mile trip, which required weeks on the fastest clipper ship, now takes ten hours. The bones arrive at a building set in the middle of Adelaide's prim botanical garden. Until recently, extracting delicate strands of DNA from a long-dead sample was science fiction. Now researchers are pulling DNA from thirty-two-thousand-year-old algae dredged from the sea floor, eighty-thousand-year-old archaic humans, and horses that lived seven hundred thousand years ago. This technology makes human companions like the chicken important markers in understanding human movement around the planet.

To see how this is done, I pay a visit to the Australian Centre for Ancient DNA. Peggy Macqueen, a youthful, round-faced woman with cropped white hair and black clothes, greets me at the entrance door. She had already told me to shower and change into clean clothes before arriving. In the foyer is a small locker room for my camera, phone, notebook, and pen. The strict protocols are designed to protect the samples from the innumerable genetic codes—not
just my own—clinging to my hands, my hair, and my very breath. Microscopic leftovers of an egg sandwich could confuse analyses of Burney's bones.

Macqueen takes me down the hall and up a flight of stairs to a changing room where we don white all-body suits, face masks, and gloves. We sit on a knee-high bench that divides the room and swing our legs over. Then she directs me to put on a second layer of latex gloves in the final staging area. Then she has me pull on a third set of gloves.

Finally we are ready to pass through an air lock and into the lab itself. As we enter, I feel a slight whoosh of air against the tiny bit of skin on my face that is not covered. The air pressure inside the lab is higher than the pressure outside to limit contamination. The room we step into is spare, with white walls, a counter, and two computer terminals. There is none of the usual lab clutter of half-filled coffee cups, clipboards, and gaping backpacks.

Macqueen guides me to a metal door in the corridor just beyond, which opens into a room the size and shape and temperature of a restaurant cooler. An entire wall of cubbyholes is filled with samples in little plastic Baggies and boxes that seem to be an inventory ­patiently waiting for a
Jurassic Park
–style revival of Siberian bison, Patagonian saber-toothed cats, and one of the world's largest mammalian carnivores, the giant short-faced bear, which weighed as much as ­thirty-five hundred pounds when it prowled American woods. All went extinct, likely at the hands of humans, about twelve thousand years ago. There is a whole section of birds and, on the other side of the cooler, a corner devoted entirely to dozens of chicken-bone samples from across the Pacific—Vanuatu, Easter Island, and four from Maukauwahi Cave that made the flight from Hawaii before mine. Chickens here qualify as something apart from birds.

Down the hall we enter a chamber of blowers, like at the tail end of a car wash. The spacious room beyond is where Macqueen cleans cartilage to remove any chemicals on the outer surface. Then she cuts a section and puts the sample in a Mikro-Dismembrator, a boxy copy-machine-sized device that, within ten seconds, pulverizes a bit
of bone into less than an aspirin's worth of powder. This she adds to a solution of enzymes designed to break down any organic material and turn the long strands of DNA into smaller and more manageable lengths. After baking it overnight at 130 degrees Fahrenheit in an incubator, Macqueen centrifuges the remaining goop at ten thousand rpm for five minutes to separate out the various components. Then she adds molecular-grade water, centrifuges the sample once again, and incubates the result for an hour or so. “You end up with nice clean DNA in nice little tiny degraded fragments,” says Macqueen, her voice slightly muffled by the mask. “And then you amplify it.”

We move into the third and most restricted part of the lab, a series of glass-walled rooms with windows looking out over the botanical garden's roses. The yellow-painted room, with space for only a desk and chair and a long and narrow counter, is designated solely for animal DNA material. This is where Macqueen uses a technique called polymerase chain reaction—PCR—to make thousands and even millions of copies of those nice little tiny degraded fragments. Even tiny surviving portions of DNA in a badly degraded bone can then be analyzed with relative ease. This obscure technology, developed in the early 1980s, won its inventors the Nobel Prize in Chemistry for opening the door to reading the genetic code embedded in all living things. “The last thing you do is add the DNA to a test tube, clean it, and put it in the machine,” she says. “You close the door, and from then on it is amplified DNA.”

The next job is to clean, clean some more, and clean again. The desk, the counter, the chair, everything must be wiped down with disinfectant to ensure that as little stray DNA remains in this room as possible. The invisible strands from one sample could contaminate the next sample that comes through the door, so such precautions are critical. She spends more time cleaning than conducting the actual work, and she must work efficiently and in isolation. You can't leave the lab for a bathroom break without going through the entire preparation protocol all over again, and tight restrictions limit how many times a day you can reenter. All food and drink, including the coffee and chocolate she likes, are forbidden. Even the building is set apart
from the rest of the campus, in the middle of the arboretum, to create yet another barrier from contamination.

Once the DNA is safely copied, she might store some in a freezer and carry the rest in a tube to the biology building, a ten-minute walk away. Until recently, she had to hurry on hot days, since high temperatures could degrade the sample. But now she uses a new chemical that stabilizes the precious material and she can stroll through the gardens on her way to campus. Still, the work is demanding and often frustrating. “Getting mitochondrial DNA out of these old bones is a struggle,” she says, reflexively wiping down a counter for a second time. “You have to decide what samples are worth a go.”

We dispose of our protective wear and Macqueen grabs her coat and leather backpack to take me to the lab's offices across campus. At a café in the garden, she tells me that she grew up on a farm in northern Australia with cattle and chickens. Later she worked in Southeast Asia on development programs designed to improve poultry for the rural poor, where they introduced the large, heavy-breasted chickens favored in the West, the birds that resulted from combining European and Asian breeds in the past century. Locals in Laos and Cambodia preferred their smaller and scrawnier birds that lay fewer eggs. “They thought their village chickens tasted a lot better, and they were right,” she says. The project failed and she moved on.

What struck her during her time in Southeast Asia was that the bird was something more than just food; it was a multipurpose animal for amusement, religious ritual, and gambling. In ancient Polynesia, the bird's meat and eggs were of course a source of fresh food on long voyages, although, like many tribal peoples of Southeast Asia, Polynesians never appear to have been major egg eaters. Instead, they used the bones for sewing and tattooing, the feathers for decoration, and the roosters as an excuse to gamble. Cockfighting was associated with religious ritual as well as entertainment. Ruaifaatoa was the god of cockfighting in Tahiti, where tradition held that chickens were made at the same time as humans.

Macqueen drops me off at the office of Alan Cooper, who directs the center and helped define the strict protocols for ancient DNA
research when it began in earnest a dozen years ago. The New Zealander has feathered hair and a boyish face and speaks quickly, as if he's perpetually late for his next meeting. “The Pacific is a basket case,” he says. For archaeologists, the vast region is no paradise. “There are not enough human bones, preservation isn't good, and it is a hard place to work.” Animal remains offer a better alternative way to chart the movement of humans, since they are more common than those of humans and don't upset locals fearful that the tombs of their ancestors will be desecrated. Not all Polynesian colonists carried the same plants and animals. No prehistoric pig or dog bones have been found on Easter Island, for example. “And rats,” says Cooper, “are a pain in the ass.” They could have stowed away on boats that traveled back and forth among islands, and their relentless comings and goings make their genetic signature even more scrambled than that of the chicken.

The bird, he adds, is proving the best way to reconstruct human colonization of the Pacific. Any chicken remains found west of Bali, the eastern edge of the red jungle fowl's home range, are signs that humans carried the bird in boats. By pinpointing combinations of DNA sequences, haplotypes assigned letters like A, B, C, and D, molecular biologists can connect the dots of this movement from west to east across the Pacific. Old bones like Burney's are rare, so the search also embraces DNA samples from modern chickens that may still contain pre-European genes. Cooper's team extracted DNA from 122 modern and 22 ancient chicken samples from across the Pacific, and discovered that the vast majority, both ancient and modern, shared the same haplotype—designated as “D.”

The ones that did not share the D group—mostly of the E ­haplotype—came from more populated areas that have a longer history of contact with the outside world in recent times. Samples that Macqueen retrieved from more remote villages of Vanuatu, six hundred miles southeast of the Solomon Islands, for example, were of the D type, as were four ancient bones found by Burney in Maukauwahi and six samples from a prehistoric site on Easter Island. This particular haplotype combines four specific genetic sequences that allow researchers to simulate various migration routes of chickens—and
therefore people—from west to east. “Polynesian chickens may be one of the few examples where ancestral genetic patterns can still be observed in a domesticated species,” Cooper and colleagues state in a 2014 paper. These birds also may still harbor some of the world's last undisturbed genetic material from precolonial chickens.

Cooper's team found that people took two primary routes. The first stretched from New Guinea to Micronesia on the northern end of Polynesian expansion. Once they reached Micronesia, a scattering of small islands, they stayed put. Some modern chickens on the isolated Micronesian island of Guam—fifteen hundred miles due east of the Philippines—contain a unique form of haplotype D not shared with other Pacific islands, while other Guam birds are linked to a subgroup found in the Philippines, Japan, and Indonesia. Micronesia was out of the mainstream of Polynesian expansion. By contrast, the ancient chickens of Easter Island and Hawaii appear to have moved across a southern route that passed through New Guinea, the Solomon Islands, and then east. The ancestors of the birds found by Burney came via Melanesia, a vast island group that includes the Solomon Islands and stretches east to Fiji.

Such finds combined with new dating of bones, pottery, and artifacts from archaeological digs across the Pacific suggest that humans took big leaps and then paused. The first and longest halt was at the Solomons, east of New Guinea, separated from the next set of islands by more than two hundred miles. By 1200 BC, when Ramses the Great was on Egypt's throne and the first chickens clucked in Egypt, early Polynesians were working their way into the open ocean as far as Fiji. There they remained until Samoa and Tonga were settled, about 900 BC. There was another long hiatus in successful voyages east, as explorers faced the daunting void in the middle of the world's largest ocean, until two millennia later, around the eleventh century AD, when settlers colonized the Society Islands in the central South Pacific. The last burst of movement took place as late as the thirteenth century—several centuries later than once thought—when Polynesians finally made landfall on the Hawaiian archipelago and Easter Island.

The origin of the culture that birthed the Polynesian expansion remains murky. Archaeologists call it Lapita, a name that comes from a site on the island of New Caledonia, halfway between New Guinea and New Zealand, that was dug in the 1950s. Since then archaeologists have found hundreds of sites with similar remains scattered throughout the region. These include stone axes, sweet potatoes, sugarcane, gourds, taro, bananas, bamboo, turmeric, pigs, rats, dogs, and chickens. There were also stowaways like snails. The people lived in houses on stilts, baked food in earthen ovens, and fished. But how these objects, plants, animals, and traditions came together, where these people came from, and how and when they spread to every major island remain hotly debated.

One view is that the Lapita people were rice-farming immigrants in China who crossed the sea to Taiwan, moved south to the Philippines and Indonesia, bypassed the inland farm peoples of larger islands like New Guinea, and then hit the open ocean. Others argue that they emerged from the mass of islands between Indonesia and the Philippines and then spread east into Melanesia and into the Pacific. A third group argues that Polynesians didn't travel to Melanesia at all but were indigenous to the area. The disagreements, which often hinge on arcane linguistic theories, reveal just how little archaeological material exists.