Criollo sheep of the Americas: the Churra flock and what it cost the maize fields
Merino wool was too valuable to export, so the sheep Spain shipped west was the coarse-wooled Churra - and five centuries later the Navajo-Churro is still genetically indistinguishable from it. The same flocks ate the fields of the Indian towns, and the law of the Indies answers with a measured distance, a forfeiture, and the right of any Indian to kill livestock found on his land without penalty.
Why this wins its question: The standard sentence is "the Spanish brought sheep", with no breed, no reason and no consequence. This object supplies all three from evidence rather than folklore: the breed was Churra because the Merino was under an export ban, and a genome-wide analysis finds "virtually no difference" between the Navajo-Churro and Spanish Churra five centuries on; the Colombian mitochondrial record adds the West African hair sheep brought in for the sugar industry through the slave trade, so the flock carries both movements; a surviving Chocholteca flock in Oaxaca numbers under a hundred animals. Then it puts the cost in the same frame and in primary text: the law of the Indies fixing half a league between sheep stations and Indian towns, doubling it for new reductions, forfeiting the estancia and half the herd, and letting any Indian kill livestock found on his land without penalty - a remedy no summary of the Laws of the Indies mentions, and evidence of the damage it answers.
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 breed that crossed was chosen by a Spanish export ban rather than by any judgment about the Americas. A genomic study of Caribbean sheep records that Spanish Churra "arrived in the Caribbean at the beginning of the 16th century with the second voyage of Columbus", and that "due to the extreme value of its wool at the time, Merinos were banned from exportation during the early stages of colonization". The hemisphere's founding flock is therefore a hardy coarse-wooled landrace, not the fine-wool breed Spain was famous for, and the reason is metropolitan protection of the Merino monopoly.
Five centuries later that ancestry is still legible without any documentary claim. The same study, comparing genome-wide structure across breeds, states that "there is virtually no difference in our structural analysis between the Navajo Churro and its accepted ancestor the Spanish Churra", the two clustering identically in admixture analysis. The sheep the Dine built a pastoral and weaving economy on is, genomically, the sheep of Old Castile.
South of that, the maternal record says the same thing and adds a second layer. A mitochondrial survey of Colombian creole sheep concludes that "creole sheep in Latin America are derived from the introduction of Iberian sheep breeds during European colonization", "introduced in South America by Spanish colonizers by the end of the fifteenth century", with the breeds "assumed" to be "Manchega, Lacha and Churra" and Castellana and Aragonesa probable contributors. Confidence sits at 0.75 for the breed names precisely because the paper marks them as an assumption of the literature rather than a result of its own genotyping.
The second layer in those genomes is the Atlantic traffic, and the paper names the industry it served: "hair sheep of West Africa were introduced during the slave trade and were intended to supply the labor demand of the sugarcane industry". American creole sheep are a record of two forced movements, not one voluntary transfer, and the African component is carried here as part of the same object rather than in a separate paragraph about something else.
On the Iberian side the group has its own signature. A survey of nineteen Iberian and six foreign breeds found three mitochondrial lineages, "B, A and C", in Iberian sheep, "with type B clearly predominating", and breeds of the Churro group showing "greater maternal uniformity" than the rest. Only the abstract of that paper rendered through this container, so nothing from its body is cited and the confidence is set accordingly.
Some of those flocks are still in indigenous hands and are nearly gone. In the Mixteca Alta of Oaxaca the zone "inhabited by the Chocholteca ethnic group, still conserves a sheep population with no more than 100 animals that present morphological characteristics similar to those introduced over 500 years ago"; the animals "became adapted to unfavorable environments and became the base of animal production"; genotyping found 205 alleles across the loci examined, an effective number of 3.33, and moderate intra-racial diversity. The continuity here is argued from morphology and locality rather than ancient DNA, which is why this is carried at 0.75.
What the flocks did to Indian agriculture is on the record in the law that tried to stop it. Recopilacion de leyes de los reynos de las Indias, libro VI, titulo III "De las Reducciones, y Pueblos de Indios", ley xx, margined to Philip III at Madrid on 10 October 1618 and to Charles II and the Queen Governor, orders "que las estancias de ganado mayor no se puedan situar dentro de legua y media de las Reducciones antiguas, y las de ganado menor media legua: y en las Reducciones que de nuevo se hicieren, haya de ser el termino dos veces tanto", on pain of forfeiting the estancia and half the livestock on it (fol. 211 of tomo II of the 1791 impression). Sheep and goats are the ganado menor of that sentence. A crown that legislates a buffer in leagues is conceding that the flocks were eating the fields.
The same law then gives the Indian towns a remedy that needs no judge. It continues, on the next page, that all owners are to keep their animals under good guard "pena de pagar el daño que hicieren: y los Indios puedan matar el ganado que entrare en su tierra, sin pena alguna" (fol. 212). Self-help against trespassing livestock, expressly free of penalty, is an unusually concrete protection to find in a compilation more often quoted for its pieties - and it is also the clearest possible statement that the damage was routine.
The grazing regime those flocks entered was legally an open commons, and the law establishing it names its own abuse. Libro IIII, titulo XVII, ley v - Charles V at Talavera on 15 April and Fuensalida on 18 October 1541, the Empress at Valladolid on 8 December 1550 - declares "que los pastos, montes, y aguas sean comunes en las Indias", and does so because "algunas personas sin titulo nuestro tienen ocupada muy grande parte de termino, y tierras en que no consiente que ninguno ponga corral, ni buhio, ni trayga alli su ganado" (fol. 57). Common pasture is what let a hemisphere fill with sheep in a century, and the enclosure the law complains of is the other half of the same story.