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.
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.
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.