In such cases, many phonologists refer not to sonority, but to a more abstract notion of relative strength, which, while once posited as universal in its arrangement, is now known to be language-specific. Syllable structure tends to be highly influenced and motivated by the sonority scale, with the general rule that more sonorous elements are internal (i.e., close to the syllable nucleus) and less sonorant elements are external. For instance, the sequence /plant/ is permissible in many languages, while /lpatn/ is much less likely. (This is the sonority sequencing principle). This rule is applied with varying levels of strictness cross-linguistically, with many languages allowing exceptions: for example, in English, /s/ can be found external to stops even though it is more sonorous (e.g. "strong", "hats"). In many languages the presence of two non-adjacent highly-sonorous elements can be a reliable indication of how many syllables are in the word; /ata/ is most likely two syllables, and many languages would deal with the sequences like /mbe/ or /lpatn/ by pronouncing them as multiple syllables, with syllabic sonorants: [m̩.be] and [l̩.pat.n̩]. The sonority ranking of speech sounds plays an important role in developing phonological patterns in language, which allows for the intelligible transmission of speech between individuals in a society. Differences in the occurrence of particular sounds in languages around the world have been observed by numerous researchers. It has been suggested that these differences are as a result of ecological pressures. This understanding was developed from the acoustic adaptation hypothesis, which was a theory initially used to understand differences in bird songs across varying habitats. However, the theory has been applied by researchers as a base for understanding why differences are shown in speech sounds within spoken languages around the world. Maddieson and Coupe’s study on 633 languages worldwide observed that some of the variation in the sonority of speech sounds in languages can be accounted for by differences in climate. The pattern follows that in warmer climatic zones, language is more sonorous compared to languages in cooler climatic zones which favour the use of consonants. To explain these differences they emphasise the influence of atmospheric absorption and turbulence within warmer, ambient air, which may disrupt the integrity of acoustic signals. Therefore, employing more sonorous sounds in a language may reduce the distortion of soundwaves in warmer climates.