range of values, allowing for the proper functioning of cells. Therefore, it has been argued that differences in the regularity of phones in a language are an adaptation which helps to regulate internal bodily temperatures. Employing the use of open vowels like /a/ which is highly sonorous, requires the opening of vocal articulators. This allows for air to flow out of the mouth and with it evaporating water which reduces internal bodily temperatures. In contrast, voiceless plosives like /t/ are more common in cooler climates. Producing this speech sound obstructs airflow out of the mouth due to the constriction of vocal articulators. Thus, reducing the transfer of heat out of the body, which is important for individuals residing in cooler climates. Vegetation A positive correlation exists, so that as temperature increases, so does the use of more sonorous speech sounds. However, the presence of dense vegetation coverage leads to the correlation occurring oppositely, so that less sonorous speech sounds are favoured by warmer climates when the area is covered by dense vegetation. This is said to be because in warmer climates with dense vegetation coverage individuals instead communicate over shorter distances, therefore favour speech sounds which are ranked lower in the sonority hierarchy. Altitude Everett, (2013) suggested that in high elevation regions such as in the Andes, languages regularly employ the use of ejective plosives like /kʼ/. Everett argued that in high altitude areas, with reduced ambient air pressure, the use of ejectives allows for ease of articulation when producing speech. Moreover, as no air is flowing out of the vocal folds, water is conserved whilst communicating, thus reducing dehydration in individuals residing in high elevation regions. A range of other additional factors have also been observed which affect the degree of sonority of a particular language such as precipitation and sexual restrictiveness. Inevitably, the patterns become more complex when considering a range of ecological factors simultaneously. Moreover, large amounts of variation are shown which may be due to patterns of migration. Mechanisms underlying differences in sonority The existence of these differences in speech sounds in modern day human language is said to be driven by cultural evolution. Language is an important part of culture. In particular, speech sounds in the sonority scale are more likely to be selected for in different environments as a language favours phonetic structures which allow for the successful transmission of messages in the presence