The turkey out of Mesoamerica: the one American livestock animal Spanish ships carried east
Almost every animal in the Columbian exchange moved west. The turkey went the other way. Penned and maize-fed in Mesoamerica long before contact, it was carried to Europe on Spanish ships in the early sixteenth century, bred into European varieties, and returned across the Atlantic in the eighteenth century as the forerunner of the commercial bird. Genetics puts the founding maternal lines in central Mexico.
Why this wins its question: The turkey is told as a Thanksgiving story or as a footnote about a misnamed bird, and the one genuinely interesting fact about it - that it is the only American livestock animal the exchange carried eastward, and that the modern industrial bird is a Mexican village animal that went to Europe and came back - is almost never assembled in one place. This object assembles it from four open-access papers read in full: the pens and the maize in the isotopes, the dated Preclassic evidence at El Mirador, the two independent domestications with no shared maternal haplotypes between them, the named haplotypes that link Michoacán backyards to the commercial Bronze line, and the eighteenth-century re-import to the Atlantic seaboard. It is explicit about what is weakest in the chain: the Spanish carriage to Europe is asserted in the introductions of genetics papers rather than from archives, and that claim is held at 0.7 and labelled. And it keeps the credit narrow - two thousand years of Mesoamerican husbandry made the animal, the crossing only moved it - while recording the Southwestern lineage that did not survive and the six village haplotypes that no programme is protecting.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The turkey is the exception in a transfer that otherwise ran one way. Of the livestock the Columbian exchange moved, cattle, pigs, sheep, horses and goats all crossed westward; "the turkey (Meleagris gallopavo) represents one of the few domestic animals of the New World", and a second study puts it more strongly still - it is "the one and only important domesticated animal species of North American origin".
The husbandry is much older than contact and it is documented, not inferred from later practice. "The earliest confirmed evidence of captively reared common turkeys has been found in the Yucatan, at the site of El Mirador, Guatemala, dating from 327 BCE to 54 CE", and other Preclassic evidence includes a complete turkey skeleton found in a burial at Oaxtepec, Morelos.
These were penned, fed birds rather than tolerated commensals: "Stable isotopes, pathological features and pollen found in coprolites indicate that turkeys were usually not 'free-range', but often enclosed in pens or corrals, and provisioned with human staples, mostly maize." Postclassic birds from western Mexico and the Gulf coast carry very high carbon-13 values, which the authors read as an intensification of that management.
There was more than one domestication, and the two were not in contact. Ancient mitochondrial DNA from 149 turkey bones and 29 coprolites across 38 archaeological sites, dated 200 BC to AD 1800, "reveals a unique domesticated breed in the precontact Southwestern United States" whose origin lies outside the region but which "rules out the South Mexican domestic turkey (Meleagris gallopavo gallopavo) as a progenitor". The Mesoamerican study finds the separation from the other direction: "No evidence of shared maternal haplotypes was observed between Mesoamerica and the Southwest USA, in contrast with archaeological evidence for trade of other domestic products."
Only one of the two lineages survived, and it is the Mexican one. "On the basis of historic accounts, however, it seems that of the two stocks, only the Mesoamerican turkey has survived into the present day as domesticates. Mexican turkeys were transported to Europe in the early 16th century and spread quickly across the continent." The Southwestern domesticated breed, the product of a strong genetic bottleneck and intensive selection, did not.
The carriers were Spanish ships, and the European bird that resulted was a Spanish-era export re-bred abroad: "After the Spanish conquerors brought the turkeys to Europe, the novelty and the appreciated meat characteristics permitted a rapid spread across Europe, starting from the 16th century." Both statements of the transfer sit in the introductions of genetics papers and rest on the secondary literature they cite rather than on archival work presented in them, which is why the confidence here is lower than for the genetic results.
The bird then made the return crossing as a European product. "Over the following centuries, several varieties of turkey were developed in Europe and later imported back to the U.S. Atlantic seaboard in the 18th century, where some became the forerunners to the commercially raised breeds known today." The industrial turkey of the twentieth century is therefore a Mexican village animal that went east, was selected in Europe, and came back.
Molecular work in Mexico locates the founding stock and connects it to the commercial lines. "Two haplotypes with different divergence times, MGMDgoB/MICH1 and MICH2, are dominant in domesticated and commercial turkeys", and those same two maternal lines "were detected in individuals of the commercial line Bronze and in domesticated individuals from Canada and the USA", so that they "probably constituted the basis of the current highly selected commercial lines". The study places the capture for domestication in the Trans-Mexican Volcanic Belt.
What is left in the villages is not a remnant of the commercial bird but a reservoir the commercial bird never sampled: the same study reports "new data on the haplotype diversity that prevails among domesticated turkeys from backyards in Mexican rural communities, with six haplotypes, which, to date, had not been reported in M. gallopavo". The authors call for sampling to be extended to Sonora, Zacatecas, Jalisco, Nayarit, Tamaulipas and the centre-south before more of it is lost.
The counterweight is that a transfer is not the same as a discovery, and the credit here is narrow. The domestication, the pens, the maize feeding and the selected bird were Mesoamerican work of some two thousand years; what the Spanish crossing added was distribution. The loss belongs in the same entry: one of the two North American domestication traditions ended with the sixteenth century, and the Mexican backyard flocks that carry the undocumented diversity have no conservation programme attached to them in either study.