Counterpoint

Reno, Nevada

I’ve talked a bit about Jane Hill‘s theory that agriculture was introduced to the Southwest by a migration of speakers of Uto-Aztecan languages from Mesoamerica, which she supports mostly through somewhat unconvincing linguistic evidence.  A recent paper in, yes, PNAS offers a strong set of counterarguments to Hill’s theory, and offers an alternative theory in which maize agriculture gradually diffused north from Mesoamerica through a chain of hunter-gatherer groups in western Mexico speaking Southern Uto-Aztecan languages.

"Plateau Country Trees" Sign, Pipe Spring National Monument

The authors, who include some fairly prominent Southwestern archaeologists, frame their argument explicitly in opposition to Hill’s, and they begin by pointing out the weakness of her linguistic arguments for a set of maize-related terms in Proto-Uto-Aztecan, which is a crucial part of her theory that the family originated in Mesoamerica and spread northward.  They also point to DNA evidence showing that Uto-Aztecan speakers in the Southwest and in Mesoamerica genetically resemble surrounding populations speaking other languages much more than they resemble each other, which mostly suggests a long period of interaction and intermarriage among neighboring groups on both ends, implying that whatever migration occurred probably happened far in the past and not providing any particular evidence for which way it went.  This evidence is interesting, and I had not seen it before.  I think it may be the strongest evidence against Hill’s theory, which only works with a relatively recent migration from south to north that would presumably show up in the genetic evidence.

Sign Describing Pinyon and Juniper, Pipe Spring National Monument

The other evidence they present, both on behalf of their own theory and against Hill’s, is quite a bit weaker, I think.  They argue for a Uto-Aztecan Urheimat in the Great Basin at the very opposite end of the current distribution of the family from Hill’s proposal of western Mesoamerica, and for a very early dispersal of the family to the south starting around 6900 BC.  They make these proposals based on evidence from the suite of terms for animals and plants that can be reconstructed for Proto-Uto-Aztecan.  As Hill noted in her papers, this set of flora and fauna is found throughout most of the current range of the languages, from the Southwest down far into Mexico, and so it doesn’t directly provide much evidence for the initial location of the protolanguage.  The authors of this paper, however, argue from negative evidence that it can be pinpointed to a northerly location at an early time.  Their reasoning is interesting: apparently two terms that cannot be reconstructed for Proto-Uto-Aztecan, even though the items they refer to occur almost everywhere Uto-Aztecan languages are spoken, are “pinyon” and “oak.”  They take this to mean that the protolanguguage was spoken in a context where there were no pinyons or oaks, and the only place they can find this to be the case is the west-central Great Basin between 9700 and 6900 BC.  Around 6900 BC conditions in the Great Basin became considerably drier, and the authors point to this event as the catalyst for the initial breakup of the Proto-Uto-Aztecan speech community with the ancestors of what would become the Southern Uto-Aztecan languages migrating south in search of wetter areas, eventually ending up in the southern Southwest and northwest Mexico, with the ancestors of Northern Uto-Aztecan speakers remaining in the north at least until pinyons began to spread northward around 5500 BC.  Later, when maize agriculture began to diffuse northward from Mexico, the Southern Uto-Aztecan groups were arranged in a long continuum along the Pacific coast and the adjacent mountains, and they passed the maize plant and knowledge of its cultivation steadily northward until it reached the southern Southwest and was adopted by local hunter-gatherer groups there, only some of which spoke Uto-Aztecan languages.  The earliest well-dated maize remains in the Southwest (mostly from the Tucson area) date to around 2100 BC, so the posited Southern Uto-Aztecan continuum must have been in place by then, which would definitely require a very early date for the initial breakup of the protolanguage if indeed it originated in the north.

Live Oak, Pipe Spring National Monument

This all makes sense, as far as it goes, but it’s really just as speculative as Hill’s theory, and as the authors point out what’s really needed to make further progress in understanding this issue is more archaeological data on the area in between Mesoamerica and the Southwest, i.e., the area through which maize would have to have passed on its way north.  They do point out one important strike against Hill’s theory, which is the lack of any clear similarities in material culture between the earliest agricultural sites in the Southwest and contemporary agricultural sites in Mesoamerica, which may argue for a diffusion of agriculture but could possibly also just mean that the migration of agriculturalists, whether or not they spoke Uto-Aztecan, took place much earlier.  Indeed, this paper appears to put the starting point for the spread of maize at the place and time of the earliest macrobotanical evidence for maize (that is, the earliest actual cobs found in the archaeological record), which comes from Guilá Naquitz Cave in Oaxaca around 4300 BC.  This is a very odd choice of place and time, however, since it is increasingly clear from starch grain and phytolith evidence, as well as genetics and the distribution of wild teosinte varieties, that maize was initially domesticated considerably earlier and further west, being definitely present in the Rio Balsas area of Guerrero by 6700 BC.  It’s particularly odd since they do in fact cite one of the recent papers presenting this evidence.  Since maize would certainly have had to initially diffuse from West Mexico to Oaxaca, there’s no reason to think there’s anything special about Oaxaca or 4300 BC from the point of view of the history of maize agriculture in general; this just happens to be the oldest setting with sufficiently good preservation to allow macrobotanical evidence to survive.  Instead, any diffusion of maize to the Southwest would certainly have begun in West Mexico, and could have begun as early as 6700 BC.  A migration at this point would be very difficult to detect in the archaeological record, and the presence of maize cultivation in the Southwest this early would also be very difficult to see.  The paper’s authors do acknowledge the possibility that maize cultivation had been going on in the Southwest before the earliest evidence of it so far discovered, but they don’t seem to really grapple with the implications of that for their theories.

Trucks at Rest Stop, Luning, Nevada

In general, I find the kind of arguments used in this sort of research interesting but not very conclusive.  The use of reconstructible terms for flora and fauna has a long history in historical linguistics, but it has not actually been very successful in pinpointing the original locations of protolanguages.  One reason for this is that terms change over time, and it’s not always clear if a given word, even if shared by most languages in a family, has the same meaning now that it had in the protolanguage.  Negative evidence of the sort used here, in particular, is problematic.  What if Proto-Uto-Aztecan did actually have a term for “pinyon” that just happened to be lost or used for another plant in several of the daughter languages?  This is very much a possibility, and it’s basically impossible to judge its likelihood based on available evidence.  Also, while using paleoclimatological data to give dates to linguistic events is an interesting idea, I do think this paper goes a bit too far with it.  There are a lot of assumptions behind the idea that a drought in the Great Basin around 6900 BC caused the breakup of Proto-Uto-Aztecan, and given that this date is much earlier than all other dates that have been proposed for this event, those assumptions really need to be critically examined.

Pinyon Trees, Pipe Spring National Monument

Nevertheless, for all its flaws, this is an interesting and important paper, particularly in the way it seeks to incorporate more lines of evidence into the ongoing debate over the introduction of agriculture to the Southwest.  There has been so much research on this topic lately, much of it overturning long-held assumptions, that it is good to see some attempts to tie it all together, even if they are ultimately unconvincing.

Merrill, W., Hard, R., Mabry, J., Fritz, G., Adams, K., Roney, J., & MacWilliams, A. (2009). The diffusion of maize to the southwestern United States and its impact Proceedings of the National Academy of Sciences, 106 (50), 21019-21026 DOI: 10.1073/pnas.0906075106