Thursday, June 30, 2022

What Drives The Distribution Of Tonal Languages And Correlated Phonetic Features?

This post was originally started and mostly written a few years ago. It is refined, expanded, and published now. (I've now cleared my backlog of draft posts.)

Languages with Complex Tone Systems

Languages With Simple Tone Systems

Languages Without Tone Systems

Languages with labial-velar consonants in yellow; 
languages with clicks in red and black.

Languages with glottal consonants other than ejectives
Purple and yellow have implosives only; 
red and white have glottalized resonants only; 
green and aqua have implosives and glottalized resonants.

Charts via WALS Online.

What is a tonal language?

In a tonal language, tone is the term used to describe the use of pitch patterns to distinguish individual words or the grammatical forms of words, such as the singular and plural forms of nouns or different tenses of verbs.

Tonality appears to be a part of a total phoneme set for a language which also includes a language's inventory of consonants, glottal stops, vowels, and click sounds. 

* The average language with a complex tone system has 26.0 consonants and 7.05 vowels, for a total of 33.05 phonemes.
* The average language with a simple tone system has 23.3 consonants and 6.28 vowels, for a total of 29.58 phonemes.
* The average language with no tone system has 22.1 consonants and 5.58 vowels, for a total of 27.68 phonemes.

Tonal languages also tend to be more likely to have implosive consonants (a type of glottal consonant), glottal resonant consonants, labial-velar consonants, and linguistic click consonants.

Where Are Tonal Languages Spoken?

As the charts at the top of this post demonstrate, tone languages tend to be more vastly common in places that with tropical (or at least subtropical) climates and very rare elsewhere. 

Languages with simple tone systems show a similar, but less pronounced tendency. All of the tonal languages outside tropical and subtropical areas have only simple tone systems. 

Some of the more controversial cases are arguable cases of simple tone systems in places where tonal languages are rare.  A dozen of the languages classified as having simple tone systems are among the most geographically atypical and are only marginally tonal to the extent that they arguably would be more properly classified as non-tonal. These include Norwegian, Japanese, Ainu and Oneida (Iroquoian; New York State).

Much of South Asia, however, despite having many languages, has a tropical or subtropical climate, but appears to have no languages with a complex tone system among its many Indo-European, Dravidian, or Austroasiatic languages, although it does have a handful of Sino-Tibetan languages with simple tone systems in the highlands found in the Himalayas and in the far northeast of the subcontinent. 

There are definitional issues about what constitutes a language with a complex tone system, a simple tone system or no tone system. WALS explains its definitions (emphasis added):
The first distinction made in this chapter is between languages with and languages without tones. For most languages it is easy to determine if the language does or does not make use of tone, but there are surprisingly sharp disagreements in certain cases. 
For example, Dar Fur Daju (Nilo-Saharan; Sudan) is reported as non-tonal in one source but transcribed with three tone levels in another. Ket (Yeniseian; northern Siberia) is described as having none, two, four or eight tones by different authors (there are some differences in the dialects being described, but this does not account for the differences of opinion on the tonal status of the language). Both these languages have been counted as non-tonal in the present chapter since the opinion that they lack tones seems to be the most well-supported (see Thelwall 1981 and Feev 1998 respectively).  
Other languages have clear word-level pitch phenomena but with limited function, or with roles that look more like stress in that they highlight a particular syllable of a word. Norwegian, Japanese, Ainu and Oneida (Iroquoian; New York State) are among languages of this kind. These languages are classified here as tonal, but are perhaps only marginally so.  
Of the 526 languages included in the data used for this chapter, 306 (58.2%) are classified as non-tonal. This probably underrepresents the proportion of the world’s languages which are tonal since the sample is not proportional to the density of languages in different areas. 
For example, from the large Niger-Congo family of Africa there are 68 languages in the sample, 5 of which are nontonal (Swahili, Diola-Fogny, Koromfe, Wolof and Bisa) and the remainder tonal. The Ethnologue (Grimes 2000) lists 1489 Niger-Congo languages, so less than 5% of the Niger-Congo languages are included. 
Of the Indo-European languages of western and central Europe, 16 are included (5 Romance, 3 Germanic, 3 Slavic, 2 Celtic, 1 Baltic, Greek, and Albanian). In these Indo-European groups the Ethnologue lists a total of 145 languages (7 Celtic, 58 Germanic, 48 Italic, 18 Slavic, 7 Greek, 4 Albanian, and 3 Baltic languages), so that over 10% of the Western European languages listed are included, only two of which are tonal or marginally so and the rest non-tonal. 
If, correspondingly, 10% of the Niger-Congo family had been included, 80 additional tone languages would have been included. 
Languages without tones predominate in the western part of the Eurasian landmass, including South Asia, in the more southerly regions of South America, and in the coastal area of northwestern North America. In this last area great genealogical diversity exists among the indigenous languages, but tone is almost entirely absent. In addition, no Australian language has been reported to be tonal.  
The languages with tones are divided into those with a simple tone system — essentially those with only a two-way basic contrast, usually between high and low levels — and those with a more complex set of contrasts. 
About a quarter of the languages (132, or 25.1%) have simple tone systems. This includes 12 languages which appear to meet the definition of being tonal only marginally. With better information a few of these might end up being classed as non-tonal. 
Less than a fifth (88, or 16.7%) have complex tone systems. Tone languages have marked regional distributions. Virtually all the languages in Africa are tonal, with the greater number having only simple tone systems, although more complex systems are not unusual, especially in West Africa. Languages with complex tone systems dominate in an area of East and Southeast Asia. Several clusters of languages with tones occur in South, Central and North America. A number of the languages of New Guinea are also tonal, or at least marginally so.

Tonality Appears To Be Primarily An Areal Rather Than A Language Family Based Property Of Languages

There are language families in which some languages are tonal, while other are not.

As noted above, two Indo-European languages arguably have simple tone systems, although at least one of these is a marginal case with a dubious classification.

Only five of Africa's Niger-Congo languages do not have tone systems.

Within the Afroasiatic language family, tonal languages appear in the Omotic, Chadic, and Cushitic branches of Afroasiatic (the Southern tier of Afroasiatic languages, mostly in Ethiopia and the African Sahel), according to Ehret (1996), but the Semitic, Berber, and Egyptian branches do not use tones phonemically.

Most Austroasiatic languages are tonal, but not the Munda languages of South Asia and not five of the lesser known Austroasiatic languages of Vietnam and Laos.

The Austronesian languages aren't uniform with regard to tonality either: "Unlike in the languages of Mainland Southeast Asia, tonal contrasts are extremely rare in Austronesian languages. Exceptional cases of tonal languages are Moklen and a few languages of the Chamic, South Halmahera–West New Guinea and New Caledonian subgroups."

The locations have temperatures and humidities that influence sound transmission through the air, and have terrain influences (e.g. tree density) that impact how far away you would need words you speak to carry best. So, one theory is that tone languages arise in places where the sound transmission qualities of the air and terrain favor them.

There have been suggestions in the literature that the local climate and ecology can make certain phoneme sets better in some places than in others, that the nature of one part of a phoneme set influences the nature of other parts of the phoneme set, and that there are specific non-random factors that favor particular subtypes of phonemes in particular conditions.
An environmental explanation is supported by the observation that tonality in language seems to be more of an areal effect than one that tracks language families.  There is a fair amount of circumstantial evidence, when you look at patterns of semantic tone use globally in all sorts of languages, to suggest that tonality is more of an areal feature than it is an indicator of the ancestral source of a language. Neighboring languages that come from different families often share the feature of semantic tonality, while languages within the same language family often differ in their use of semantic tonality.
Incidentally, the geographic distribution of languages with tone systems is similar, although not identical, to the geographic distribution of languages with glottal consonants. Both are most common in sub-Saharan Africa, Southeast Asia, and the subtropical and tropical regions of the Americas (although the Americas are far from uniform despite all except the Na-Dene and Inuit language families probably having a common ancestor ca. 14kya). But, the Chinese dialect family uses tone, while it does not utilize glottal consonants. 
It could be that the ancestral hominin type ASPM gene correlated with tonal languages “tunes” ones hearing system to better distinguish sounds in a certain pitch range, in general, in places that that the temperatures, humidities and terrain most conducive to tonal languages, while the derived type ASPM gene loosens to focus of the hearing system so that it isn’t so primed to maximizing hearing of sounds in particular set of conditions, which would be adaptive elsewhere.
This is a more complex hypothesis than the one proposed in the paper showing a relationship between tonal languages and this gene. This 2007 paper and abstract are as follows:
The correlations between interpopulation genetic and linguistic diversities are mostly noncausal (spurious), being due to historical processes and geographical factors that shape them in similar ways. Studies of such correlations usually consider allele frequencies and linguistic groupings (dialects, languages, linguistic families or phyla), sometimes controlling for geographic, topographic, or ecological factors. 
Here, we consider the relation between allele frequencies and linguistic typological features. Specifically, we focus on the derived haplogroups of the brain growth and development-related genes ASPM and Microcephalin, which show signs of natural selection and a marked geographic structure, and on linguistic tone, the use of voice pitch to convey lexical or grammatical distinctions. 
We hypothesize that there is a relationship between the population frequency of these two alleles and the presence of linguistic tone and test this hypothesis relative to a large database (983 alleles and 26 linguistic features in 49 populations), showing that it is not due to the usual explanatory factors represented by geography and history. The relationship between genetic and linguistic diversity in this case may be causal: certain alleles can bias language acquisition or processing and thereby influence the trajectory of language change through iterated cultural transmission.

Earlier versions still of this gene are associated with brain size:
The size of human brain tripled over a period of approximately 2 million years (MY) that ended 0.2-0.4 MY ago. This evolutionary expansion is believed to be important to the emergence of human language and other high-order cognitive functions, yet its genetic basis remains unknown. An evolutionary analysis of genes controlling brain development may shed light on it. ASPM (abnormal spindle-like microcephaly associated) is one of such genes, as nonsense mutations lead to primary microcephaly, a human disease characterized by a 70% reduction in brain size. Here I provide evidence suggesting that human ASPM went through an episode of accelerated sequence evolution by positive Darwinian selection after the split of humans and chimpanzees but before the separation of modern non-Africans from Africans. Because positive selection acts on a gene only when the gene function is altered and the organismal fitness is increased, my results suggest that adaptive functional modifications occurred in human ASPM and that it may be a major genetic component underlying the evolution of the human brain.
The case that your ASPM variant enhances fitness primarily by making your hearing system better adapted to your primary environment makes more sense to me in an evolutionary selective fitness sense. If people with the region appropriate variant hear subtle slight sound differences better than people who lack it, that could increase the ability of a hunter-gatherer to locate prey, to detect predators, to locate lost children who have wandered far away, to hear your enemies coming to get you, to detect a fire that has gotten out of control or something that you are standing on that is about to break, and cumulatively, that could produce a gradual, put persistent selective fitness advantage in the evolutionary sense.
I find it harder to believe that the tone language specific application of this trait would have much of a selective fitness effect. An inability to distinguish by sound alone two words that would both make contextual sense in a tonal language that you and the speaker share might tweak one’s social status in the community a little, but it seems less likely to have a big impact on mortality or lifetime reproductive success. It’s not impossible, but it would seem like a weaker explanation.
Against this backdrop, the natural question to ask is one that wouldn’t otherwise be obvious, which is “why aren’t there more tonal language in South Asia?” which has substantial linguistic diversity and climate features in part of the region that are very similar to places in Africa, Southeast and East Asia, and the Americas where tonal languages are predominant.
One partial answer to this is that the Indo-Aryan languages developed in places that did not have this climate and didn’t spontaneously pick up this feature upon arriving in the subcontinent. 
Migration can also explain the affirmative presence of these features in arid southern Africa where people speaking these languages probably migrated from more tropical parts of Eastern sub-Saharan Africa.
But, this doesn’t explain why we don’t see tonal Munda and Dravidian languages in South Asia. The urheimat of the Austroasiatic languages of which the Munda languages are a family member, is Southeast Asia (or perhaps southern China), where the vast majority of languages are tonal. And, the Dravidian languages, as far as anyone knows, are autochthonous in South Asia.
In both of these exception cases, I think that the likely explanation is a language learner effect.
The Munda languages, at least initially, seem to have had a fairly northerly distribution within South Asia where hearing well suited to tonality wouldn’t have been advantageous to the local people who probably accounted for all or most of the women in the community at the time of first contact when the Munda languages would have been adopted by people integrated into the early Munda communities. If half the people had trouble hearing the tones, that feature which was almost surely present in an ancestral pre-Munda language probably didn’t survive.
In the case of the Dravidian languages, which probably have an ancestral version that was tonal under the environmental hypothesis, the pertinent fact is that there are no meaningful communities in Dravidian India that do not have substantial ANI admixture dating to the last 2000-3500 years. The language learner affect at the time of ANI-ASI admixture could have stripped the Dravidian languages in existence at the time of their tonal features for the same reasons. The ubiquity of the Hindu religion in Dravidian India which has clear Indo-Aryan and Harappan synthesis origins, likewise suggests that the language learners were not just anybody, they were culturally influential elites whose language choices tend to influence whole communities by cultural imitation.

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