The first decades of the 21st century have witnessed a renewed interest in the relationship between language structure and the various social and ecological niches in which the languages of the world are used and against the background of which they evolved. In this context, Everett (2013) argued for direct geographical influences on the sound structure of languages. It was observed that ejective consonants, produced with a sudden burst of non-pulmonic air to a salient acoustic effect, tend to occur in high-altitude environments in which these sounds may be adaptive due to a reduced articulato the idea that “[T]he serrated close way of Speaking of Northern Nations, may be owing to their Reluctance to open their Mouth wide in cold Air, which must make their Language abound in Consonants; whereas from a contrary Cause, the Inhabitants of warmer Climates opening their Mouths, must form a softer Language, abounding in Vowels” [ 17 , pg. 153-154]). Concretely, we seek to shed additional light on the possible role of the geophysical environment in which languages are spoken on the sound structure of human languages, which has been a central arena of theorizing in both phases in which research on the language-environment interface flourished. Specifically, we investigate one major claim regarding a possible effect of the environment on phonological structures that has been put forward recently, and put it into a broader empirical and theoretical context. For instance, general mechanisms of expanding and saturating phoneme inventories, e.g., system-internal factors that are not yet understood, could very well be involved. Here, we explore a particular alternative hypothesis that does make reference to physical geography, but in a more indirect fashion that is mediated by sociolinguistic patterns of language use. Mountain environments with their challenging topography are commonly thought of as having the effect of isolating human communities and limiting communication between them. By reassessing the validity of the association between ejectives and altitude through a different dataset and by using different analytical techniques, we also contribute to a recent plea for robustness and incremental approaches in the assessment of specific hypotheses relating to the adaptive potential of human language [ 19 ]. However, we also emphasize that our study is not meant as a mere critical re-evaluation of Everett [ 21 ] in a narrow sense. By examining the distribution of uvular consonants in light of the same predictive parameter, i.e. We have included altitude as computed according to the procedure described in Section Altitude data as a fixed effect after applying a log10-transformation. This is because of an extreme left skew in the distribution of the altitudes at which languages are spoken—as human populations are typically much denser at low altitudes [ 28 ], so is apparently language density. Note that because of the transformation, four further languages could not be taken into account for modelling, leaving a set of 2,031 languages for analysis. These diachronic perspectives are at the heart of recent research in distributional typology [ 69 , 70 ]. To assess the diachronic dynamics of both classes of sounds within language families, we chose to look at Indo-European and Sino-Tibetan—two large and old language families of Eurasia, for which there exist high-resolution computationally-generated language phylogenies. In Ossetic, direct loans from Nakh-Daghestanian account for the ejectives in most languages’ lexical items [ 81 ], but there is also regular sound change that gives rise to them and that likewise can plausibly be theorized to have been triggered by Nakh-Daghestanian influence [ 82 – 84 ]. Note too, that recent work by Eisen [ 85 ], who investigates segment borrowing patterns in a large sample of languages [ 86 ], suggests the implicational universal that if a language borrows an ejective, then it already has at least one. Of course this literature review is selective, and there are cases including Turkic and Mongolic, where uvulars arose apparently entirely from internal sources through the phonologization of an originally allophonic variation in the context of back vowels that still persists in some languages [ 77 ]. However, the present-day distribution of uvulars is strongly influenced by local areal factors, and language contact seems to have played a significant role in its genesis. For example, Matras [ 99 , pg. 270] considers a uvular stop as an areal feature of present-day Anatolia. Even though it seems clear for some cases surveyed here that contact was the main driver for the diachronic development of ejectives and uvulars, could this perhaps be only the proximate reason? And could the ultimate reason why they were replicated through contact be an adaptation to high-altitude environments such as those of the Northern Caucasus and Eastern Tibet through language contact effects? The extant literature is often Janus-faced when it comes to this question [ 14 ]. Moreover, regarding the Quechuan-Aymaran case, there is strong evidence that the factor that motivated the adoption of ejectives in Quechuan and that facilitated their spread through the native Quechuan lexicon were iconic values associated with them locally [ 108 , 109 ]. Any argument that would seek to posit adaptiveness as a still more basic principle behind the diachronic developments would be faced with the challenge to factor this fact in. These cases are representative of a more common cross-linguistic pattern. PHOIBLE contains data from 248 different language families (including isolates as singleton families). Of these, only 68 (circa 28%) feature uvular consonants, and only 65 (circa 26%) ejective consonants, highlighting once more the relative rarity of both classes of speech sounds. There is no logical necessity that both classes of sounds should co-occur in the same languages and language families.

Human sound systems are shaped by post-Neolithic changes in bite configuration | Science Advertisement Contents ## The first fricatives In 1985, the linguist Charles Hockett proposed that the use of teeth and jaws as tools in hunter-gatherer populations makes consonants produced with lower lip and upper teeth (“f” and “v” sounds) hard to produce. He thus conjectured that these sounds were a recent innovation in human language. Blasi et al. combined paleoanthropology, speech sciences, historical linguistics, and methods from evolutionary biology to provide evidence for a Neolithic global change in the sound systems of the world's languages. Spoken languages have thus been shaped by changes in the human bite configuration owing to changes in dietary and behavioral practices since the Neolithic. Science, this issue p. eaav3218 ## Structured Abstract ### INTRODUCTION Human speech manifests itself in spectacular diversity, ranging from ubiquitous sounds such as “m” and “a” to the rare click consonants in some languages of southern Africa. This range is generally thought to have been fixed by biological constraints since at least the emergence of Homo sapiens. At the same time, t