Depending on the age of the language family under consideration, its homeland may be known with near-certainty (in the case of historical or near-historical migrations) or it may be very uncertain (in the case of deep prehistory). Next to internal linguistic evidence, the reconstruction of a prehistoric homeland makes use of a variety of disciplines, including archaeology and archaeogenetics.
There are several methods to determine the homeland of a given language family. One method is based on the vocabulary that can be reconstructed for the proto-language. This vocabulary – especially terms for flora and fauna – can provide clues for the geographical and ecological environment in which the proto-language was spoken. An estimate for the time-depth of the proto-language is necessary in order to account for prehistorical changes in climate and the distribution of flora and fauna.
Another method is based on the linguistic migration theory (first proposed by Edward Sapir), which states that the most likely candidate for the last homeland of a language family can be located in the area of its highest linguistic diversity. This presupposes an established view about the internal subgrouping of the language family. Different assumptions about high-order subgrouping can thus lead to very divergent proposals for a linguistic homeland (e.g. Isidore Dyen's proposal for New Guinea as the center of dispersal of the Austronesian languages). The linguistic migration theory has its limits because it only works when linguistic diversity evolves continuously without major disruptions. Its results can be distorted e.g. when this diversity is wiped out by more recent migrations.
The concept of a (single, identifiable) "homeland" of a given language family implies a purely genealogical view of the development of languages. This assumption is often reasonable and useful, but it is by no means a logical necessity, as languages are well known to be susceptible to areal change such as substrate or superstrate influence.
Over a sufficient period of time, in the absence of evidence of intermediary steps in the process, it may be impossible to observe linkages between languages that have a shared Urheimat: given enough time, natural language change will obliterate any meaningful linguistic evidence of a common genetic source.
This general concern is a manifestation of the larger issue of "time depth" in historical linguistics.
For example, the languages of the New World are believed to be descended from a relatively "rapid" peopling of the Americas (relative to the duration of the Upper Paleolithic) within a few millennia (roughly between 20,000 and 15,000 years ago), but their genetic relationship has become completely obscured over the more than ten millennia which have passed between their separation and their first written record in the early modern period. Similarly, the Australian Aboriginal languages are divided into some 28 families and isolates for which no genetic relationship can be shown.
The Urheimaten reconstructed using the methods of comparative linguistics typically estimate separation times dating to the Neolithic or later. It is undisputed that fully developed languages were present throughout the Upper Paleolithic, and possibly into the deep Middle Paleolithic (see origin of language, behavioral modernity). These languages would have spread with the early human migrations of the first "peopling of the world", but they are no longer amenable to linguistic reconstruction. The Last Glacial Maximum (LGM) has imposed linguistic separation lasting several millennia on many Upper Paleolithic populations in Eurasia, as they were forced to retreat into "refugia" before the advancing ice sheets. After the end of the LGM, Mesolithic populations of the Holocene again became more mobile, and most of the prehistoric spread of the world's major linguistic families seem to reflect the expansion of population cores during the Mesolithic followed by the Neolithic Revolution.
The Nostratic theory is the best-known attempt to expand the deep prehistory of the main language families of Eurasia (excepting Sino-Tibetan and the languages of Southeast Asia) to the beginning of the Holocene. First proposed in the early 20th century, the Nostratic theory still receives serious consideration, but it is by no means generally accepted. The more recent and more speculative "Borean" hypothesis attempts to unite Nostratic with Dené–Caucasian and Austric, in a "mega-phylum" that would unite most languages of Eurasia, with a time depth going back to the Last Glacial Maximum.
The argument surrounding the "Proto-Human language", finally, is almost completely detached from linguistic reconstruction, instead surrounding questions of phonology and the origin of speech. Time depths involved in the deep prehistory of all the world's extant languages are of the order of at least 100,000 years.
The concept of an Urheimat only applies to populations speaking a proto-language defined by the tree model. This is not always the case.
For example, in places where language families meet, the relationship between a group that speaks a language and the Urheimat for that language is complicated by "processes of migration, language shift and group absorption are documented by linguists and ethnographers" in groups that are themselves "transient and plastic." Thus, in the contact area in western Ethiopia between languages belonging to the Nilo-Saharan and Afroasiatic families, the Nilo-Saharan-speaking Nyangatom and the Afroasiatic-speaking Daasanach have been observed to be closely related to each other but genetically distinct from neighboring Afroasiatic-speaking populations. This is a reflection of the fact that the Daasanach, like the Nyangatom, originally spoke a Nilo-Saharan language, with the ancestral Daasanach later adopting an Afroasiatic language around the 19th century.
Creole languages are hybrids of languages that are sometimes unrelated. Similarities arise from the creole formation process, rather than from genetic descent. For example, a creole language may lack significant inflectional morphology, lack tone on monosyllabic words, or lack semantically opaque word formation, even if these features are found in all of the parent languages of the languages from which the creole was formed.
Some languages are language isolates. That is to say, they have no well accepted language family connection, no nodes in a family tree, and therefore no known Urheimat. An example is the Basque language of Northern Spain and southwest France. Nevertheless, it is a scientific fact that all languages evolve. An unknown Urheimat may still be hypothesized, such as that for a Proto-Basque, and may be supported by archaeological and historical evidence.
Sometimes relatives are found for a language originally believed to be an isolate. An example is the Etruscan language, which, even though only partially understood, is believed to be related to the Rhaetic language and to the Lemnian language. A single family may be an isolate. In the case of the non-Austronesian indigenous languages of Papua New Guinea and the indigenous languages of Australia, there is no published linguistic hypothesis supported by any evidence that these languages have links to any other families. Nevertheless, an unknown Urheimat is implied. The entire Indo-European family itself is a language isolate: no further connections are known. This lack of information does not prevent some professional linguists from formulating additional hypothetical nodes (Nostratic) and additional homelands for the speakers.
Inherited tree names seem to indicate a Uralic homeland to the east of the Ural Mountains. The internal branching of the family suggests an area between the Ob River and Yenisey River. Uralic speakers are not genetically distinguished from their neighbours, but do share a genetic component that is of Siberian origin.
All modern Koreanic varieties are descended from the language of Unified Silla, which ruled the southern two-thirds of the Korean peninsula between the 7th and 10th centuries. Evidence for the earlier linguistic history of the peninsula is extremely sparse. The orthodox view among Korean social historians is that the Korean people migrated to the peninsula from the north, but no archaeological evidence of such a migration has been found.
The reconstruction of Sino-Tibetan is much less developed than for other major families, so its higher-level structure and time depth remain unclear. Proposed homelands and periods include: the upper and middle reaches of the Yellow River about 4–8 kya, associated with the hypothesis of a top-level branching between Chinese and the rest; southwestern Sichuan around 9 kya, associated with the hypothesis that Chinese and Tibetan form a subbranch; Northeast India (the area of maximal diversity) 9–10 kya.
Austroasiatic is widely held to be the oldest family in mainland Southeast Asia, with its current discontinuous distribution resulting from the later arrival of other families. The various branches share a great deal of vocabulary concerning rice cultivation, but few related to metals. Identification of the homeland of the family has been hampered by the lack of progress on its branching. The main proposals are Northern India (favoured by those who assume an early branching of Munda), Southeast Asia (the area of maximal diversity) and southern China (based on claimed loanwords in Chinese).
The homeland of the Austronesian languages is widely accepted by linguists to be Taiwan, since nine of its ten branches are found there, with all Austronesian languages found outside Taiwan belonging to the remaining Malayo-Polynesian branch.
Some authorities on the history of the Uto-Aztecan language group place the Proto-Uto-Aztecan homeland in the border region between the USA and Mexico, namely the upland regions of Arizona and New Mexico and the adjacent areas of the Mexican states of Sonora and Chihuahua, roughly corresponding to the Sonoran Desert. The proto-language would have been spoken by foragers, about 5,000 years ago. Hill (2001) proposes instead a homeland further south, making the assumed speakers of Proto-Uto-Aztecan maize cultivators in Mesoamerica, who were gradually pushed north, bringing maize cultivation with them, during the period of roughly 4,500 to 3,000 years ago, the geographic diffusion of speakers corresponding to the breakup of linguistic unity.
There is no consensus on the location of the Afroasiatic homeland, though based on current evidence somewhere in the eastern Sahara or adjacent regions is considered most likely. Proto-Afroasiatic is estimated to have begun to break up in the 8th millennium BCE.Proto-Semitic is thought to have been spoken in the Near East between 4400 and 7400 BCE, with Akkadian representing its earliest known branch.
Valentin Vydrin concluded that "the Mande homeland at the second half of the 4th millennium BC was located in Southern Sahara, somewhere to the North of 16° or even 18° of Northern latitude and between 3° and 12° of Western longitude." That is now Mauritania and/or southern Western Sahara.
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