Some Oto-Manguean languages are moribund or highly endangered; for example, Ixcatec and Matlatzinca each have fewer than 250 speakers, most of whom are elderly.

The internal diversity is comparable with that of Indo-European, and the Proto-Oto-Manguean language is estimated to have been spoken some time before 2000 BCE.

A genetic relationship between Zapotecan and Mixtecan was first proposed by Manuel Orozco y Berra in 1864; he also included Cuicatec, Chocho and Amuzgo in his grouping.

In 1865, Pimentel added Mazatec, Popoloca, Chatino and Chinantec – he also posed a separate group of Pame, Otomi and Mazahua, the beginning of the Oto-Pamean subbranch.

[clarification needed] In 1920, Walther Lehmann included the Chiapanec–Mangue languages and correctly established the major subgroupings of the Oaxacan group.

Proto-Oto-Pamean was reconstructed by Doris Bartholomew, Proto-Zapotecan by Morris Swadesh, Proto-Chiapanec–Mangue by Fernández de Miranda and Weitlaner.

[3] In spite of the lack of a full published reconstruction of proto-Oto-Manguean, the language family has now been widely accepted by specialists, including Lyle Campbell, Terrence Kaufman, and William Poser.

Campbell and Poser writing in 2008 concluded that ""Tlapanec-Subtiaba proved not to belong to 'Hokan' as postulated by Sapir (1925a), but to be a branch of Otomanguean ..."" Nonetheless, a few studies have retained the inclusion in Hokan, particularly Joseph Greenberg's widely rejected 1987 classification,[4] as well as its derivative works by Merritt Ruhlen.

Swadesh (1960) and Rensch included the Huave language as a separate branch within Oto-Manguean, but this inclusion has proved untenable as most of the cognates were loan-words from Zapotec.

They call for a redoubling of the effort to document and reconstruct several important branches that have received little attention: principally Mixtecan, Popolocan and Oto-Pamean.

[9] Otomi Mazahua Matlatzinca Chichimeca (Jonaz) Pamean Chinantec Tlapanec Subtiaba Manguean Chocho Popoloca Ixcatec Mazatecan Zapotecan Amuzgo Mixtec Trique Cuicatec Some early classifications such as that by Brinton, considered that Oto-Manguean languages might be related to Chinese, because like Chinese the languages were tonal and mostly monosyllabic.

[10] Edward Sapir included Subtiaba–Tlapanec in his Hokan phylum, but didn't classify the other Oto-Manguean languages in his famous 1929 classification.

Oto-Mangue speakers have been among the earliest to form highly complex cultures of Mesoamerica: the archeological site of Monte Albán with remains dated as early as 1000 BCE is believed to have been in continuous use by Zapotecs.

Other Mesoamerican cultural centers which may have been wholly or partly Oto-Manguean include the late classical sites of Xochicalco, which may have been built by Matlatzincas, and Cholula, which may have been inhabited by Manguean peoples.

The Zapotecs are among the candidates to have invented the first writing system of Mesoamerica – and in the Post-Classic period the Mixtecs were prolific artisans and codex painters.

During the postclassic the Oto-Manguean cultures of Central Mexico became marginalized by the intruding Nahuas and some, like the Chiapanec–Mangue speakers went south into Guerrero, Chiapas and Central America, while others such as the Otomi saw themselves relocated from their ancient homes in the Valley of Mexico to the less fertile highlands on the rim of the valleys.

Because of recent migratory patterns, small populations of Otomi speakers can be found in new locations throughout Mexico and in the United States.

[16] The Chinantecan languages are spoken by c. 93,000 people in Northern Oaxaca and Southern Veracruz in the districts of Cuicatlán, Ixtlán de Juárez, Tuxtepec and Choapan.

They are all traditionally spoken in central and southern Oaxaca, but have been spread throughout Mexico and even into the United States through recent labor related migrations.

[17] The Mixtecan languages are traditionally spoken in the region known as La Mixteca, which is shared by the states of Oaxaca, Puebla and Guerrero.

Because of migration from this region the Mixtecan languages have expanded to Mexico's main urban areas, particularly the State of México and the Federal District, to certain agricultural areas such as the San Quintín valley in Baja California and parts of Morelos and Sonora, and even into the United States.

[18] The number of varieties of Mixtec depends in part on what the criteria are for grouping them, of course; at one extreme, government agencies once recognized no dialectal diversity.

Mutual intelligibility surveys and local literacy programs have led SIL International to identify more than 50 varieties which have been assigned distinct ISO codes.

In most Oto-Manguean languages tone serves to distinguish both between the meanings of roots and to indicate different grammatical categories.

Particularly common in the Oto-Pamean branch are small tonal systems with only two level tones and one contour, such as Pame and Otomi.

Syllable initial consonant clusters are very limited, usually only sibilant-CV, CyV, CwV, nasal-CV, ChV, or CʔV are allowed.

These are some of the most simple sound changes that have served to divide the Oto-Manguean family into subbranches: The following lexical reconstructions of Proto-Oto-Manguean are from Kaufman (1983).