Indo-European copula copula (with corresponding voiceless and voiced fricatives) existed side by side in Germanic, and the involvement of a separate root "" is unnecessary. The root "*(s)teh-" meant "to stand". From this root comes the present stem of the so-called "substantive verb" in Irish and Scottish Gaelic, "tá" and "tha" respectively. On the absence of the initial s- in Celtic, see Indo-European s-mobile. In Latin, "stō, stare" retained the meaning "to stand", until local forms of Vulgar Latin began to use it as a copula in certain circumstances. Today, this survives in that several Romance languages (Galician-Portuguese, Spanish, Catalan) use it
Indo-European migrations change of vegetation, triggering "higher mobility and transition to the nomadic cattle breeding". Water shortage also had a strong impact in south Asia, "causing the collapse of sedentary urban cultures in south central Asia, Afghanistan, Iran, and India, and triggering large-scale migrations". The Proto-Indo-European Urheimat hypotheses are tentative identifications of the "Urheimat", or primary homeland, of the hypothetical Proto-Indo-European language. Such identifications attempt to be consistent with the glottochronology of the language tree and with the archaeology of those places and times. Identifications are made on the basis of how well, if at all, the projected migration routes and times