Revered by the Aztecs, devoured by millions: today’s titanic turkey is a very different bird to its flighty ancestors
STUFFED and trussed and served with gravy and all the trimmings, for many of us turkey is synonymous with the holidays. At Christmas (and Thanksgiving), families across much of the western world consider that all-important question: white meat or brown? Few, however, will have wondered how a bird with an impeccable pedigree has been transformed into the avian monstrosity at the centre of their festive feasts.
For hundreds of years, turkeys were revered in their native North America: the Aztecs deified them, the Mayans sacrificed them in petitions for water, and they feature in the origin myths of the Zuni people. This reverence was well deserved. Wild turkeys are majestic creatures with spectacular plumage. They also have keen eyesight and hearing, are fleet of foot and can fly at speeds of over 80 kilometres an hour.
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It is hard to believe that the Christmas-dinner favourite originates from the same stock. A lumbering 20-kilogram gobbler is twice the size of its largest wild relative – too heavy to fly, or even to mate. How did the turkey go from venerated bird to muscle-bound foodstuff?
Today the wild turkey, Meleagris gallopavo, is native to much of the eastern and south-western US and Mexico, and falls into six distinct subspecies (see map). Exactly when it was domesticated is a mystery, but we know that the pre-Aztec residents of what is now southern Mexico reared turkeys, and by 250 BC the birds were an important resource for the indigenous people of the south-west of North America.
Until recently it had been widely assumed that these Native Americans acquired domestic turkeys from the ancient people of Mesoamerica. Earlier this year, Camilla Speller and colleagues at Simon Fraser University in Burnaby, British Columbia, Canada, showed otherwise. By analysing DNA from ancient turkey bones and fossilised turkey droppings, they found that the turkeys reared in what is now the US Southwest were genetically distinct from their Mexican counterpart to the south. Clearly the two had separate origins. Where did the more northerly variety come from? We still have little idea, but we do know they weren’t local. A second DNA comparison, this time involving the eastern and Rio Grande wild turkeys, the subspecies that now live in the region, also revealed a high degree of genetic difference ().
Speller, now at the University of Calgary in Alberta, is still trying to pin down the origin of the more northerly turkeys. What is clear is that they were bred intensively: she found that the domestic birds were inbred, and were probably descended from a small founder population. As local breeding efforts took off, birds from that single stock appear to have been traded among the various Pueblo groups in the region.
Meanwhile, the archaeological evidence leaves no doubt that these birds were highly valued. Bone markings left by butchery and cooking indicate that turkey was on the menu by about AD 1000. Before that, however, the bird’s hottest commodity was its feathers. “We know from ethnographic records that feathers were used to make robes and blankets,” says Speller. “Turkey feathers were also used in rituals and on prayer sticks. Sometimes we even see turkey interred with human burials.”
Another new study throws more light on pre-Columbian turkey farming in the region. Archaeologist Brooklynne Fothergill at the University of Leicester, UK, has been looking at old turkey bones – particularly at signs of disease and patterns of injury – to find out about the people who reared the birds. Examining collections of turkey bones dating from after 1150, unearthed in the US Southwest, she found several birds had suffered a fracture in the middle of one of the wing bones, the ulna, something she says is “extremely unlikely to occur” during normal activity. She suspects human keepers inflicted the injuries to prevent their turkeys escaping – a possible early version of the modern poultry-keeping practice of pinioning, in which part of the wing is surgically removed to keep the birds grounded.
Fothergill is also intrigued by a leg bone from Utah that dates from around 1250, which was broken mid-shaft and healed without any sign of infection. She notes that the injured bird is unlikely to have survived without human help. “Whether this was a turkey that was destined to provide feathers or to be food, either way, it wasn’t just discarded,” she says. “Somebody cared enough to look after it.” The indigenous people may have lovingly tended their birds, but ultimately this branch of the turkey family tree was doomed. Eventually the Spanish arrived, the local cultures were heavily repressed, and the domestic turkey native to what is now the American Southwest went the way of the dodo.
Discarded bones
Fortunately for lovers of the big-breasted Christmas entrée, the domestic turkey lived on in southern Mexico. Turkey bones from as early as 800 BC have been unearthed in archaeological digs there, but it is not clear whether the birds had been domesticated by that point. The problem is that the early domestic turkey so closely resembled the local subspecies of wild turkey from which it descended that it is difficult to tell whether these ancient turkey bones come from domesticated birds or wild ones. AD 180 or thereabouts is the earliest date that we can place domestic turkeys in southern Mexico, using clear evidence of domestication such as plentiful turkey droppings and eggshells inside human settlements.
Still, there is no doubt that the Mexican domestic turkey was the forebear of the modern variety. European explorers arrived in Mesoamerica to find bedraggled birds that were clearly being raised for their feathers. “Spanish records describe these really ragged-looking turkeys that had been recently plucked,” says Fothergill. Despite the birds’ bedraggled appearance, the Spanish found turkey very much to their taste, and by 1520 they had brought the bird home with them. It was a big hit. “The turkey took Europe by storm,” Fothergill says. “It was easier to raise than peacock. It looked very nice on the dinner table. You could impress people with it.”
Even so, the European domestic variety maxed out at about 10 kilograms – considerably less meaty than the bird slaughtered for the table today. It was the plumage that breeders were initially more interested in. They busied themselves creating breeds with different colour traits, says Kent Reed at the University of Minnesota in St Paul. The gradual transformation of the domestic turkey continued over the next two centuries, but the birds never reached anything like the huge proportions of today’s 20-kilo-plus broad-breasted whites. It wasn’t until the mid to late 1950s that turkeys “really went commercial”, says Reed, and began to be bred with industrial-scale production in mind.
In the half-century since, we have managed to turn M. gallopavo into a feathered monster with shortened legs and a grossly oversized breast. And it doesn’t just grow big – it also grows quickly. In 1960, a typical 6-month-old turkey weighed in at around 11 kilos. Today, a commercially reared turkey of the same age can be double that weight. Some males, or toms, can swell to as much as 30 kilos and, although females are generally quite a bit smaller, they too dwarf their wild relatives. The unnatural girth comes at a cost. Males can no longer mount their mates without crushing them, so commercial turkeys have to be bred by artificial insemination. The birds are also much too heavy to fly.
That is good news for lovers of white meat. The well-exercised breast muscles of wild turkeys are naturally dark. Working muscles need oxygen for fuel, and heavily used muscles contain more of the protein myoglobin, which binds to oxygen. The domestic turkey’s oversized, underused breast contains little myoglobin and is therefore snowy white. It also has a sweet and delicate taste, whereas the wild bird has a strong, gamey flavour.
“The well-exercised breast muscles of wild turkeys are naturally dark with a gamey flavour”
By selecting for characteristics such as size or rapid growth, commercial breeders have tried to steer turkey evolution one trait at a time. A more sophisticated, high-tech approach should become feasible with the publication of the domestic turkey genome earlier this year ().
The turkey is only the third bird to have its genome sequenced, after the chicken and the zebra finch. Adding this extra avian to the mix will help scientists better understand bird biology, says Rami Dalloul at Virginia Tech University in Blacksburg who, along with Reed, was involved in the project. The turkey was an obvious species to choose, he says: it is an important livestock species, and turkey consumption has tripled in the past 25 years.
So far, genetic comparisons indicate that domestic turkeys remain closely related to wild ones. But there seem to be important variations in some genes associated with the functioning of the immune system. “We’re pretty sure there are major differences when it comes to disease resistance,” says Dalloul. Domestic turkeys are very susceptible to aflatoxins, for instance – poisons produced by fungi that grow on corn and other crops, which are deadly at high doses and have been linked to cancer at low doses. With the genome to hand it may now be possible to pinpoint the genes that make wild turkeys more resistant.
Such insights would be of great value to turkey producers. So too will the work of Dalloul’s group, which is searching turkey DNA for single base-pair changes linked with particular physical traits or disease susceptibility. By screening for these, breeders could select for birds that have good commercial characteristics such as tender meat or high egg yield, while simultaneously improving disease resistance and health.
It is too soon to say how modern genetic techniques will change the turkey, but it is not too late to appreciate this extraordinary bird for what it has already become. Although it may seem to have fallen far since its days as an Aztec god, perhaps the turkey’s makeover has created a truly modern icon. After all, it possesses many of the attributes we most admire in a bird. And even if the modern commercially bred variety lacks some of the allure of its wild cousins, at this time of year, every turkey at least gets its 15 minutes of fame.
