The term Aryan has been used historically to denote the Indo-Iranians, because Arya is the self designation of the ancient speakers of the Indo-Iranian languages, specifically the Iranian and the Indo-Aryan peoples, collectively known as the Indo-Iranians. Some scholars now use the term Indo-Iranian to refer to this group, while the term "Aryan" is used to mean "Indo-Iranian" by other scholars such as Josef Wiesehofer and Jaakko Häkkinen. Population geneticist Luigi Luca Cavalli-Sforza, in his 1994 book The History and Geography of Human Genes, also uses the term Aryan to describe the Indo-Iranians.
The early Indo-Iranians are commonly identified with the descendants of the Proto-Indo-Europeans known as the Sintashta culture and the subsequent Andronovo culture within the broader Andronovo horizon, and their homeland with an area of the Eurasian steppe that borders the Ural River on the west, the Tian Shan on the east. Historical linguists broadly estimate that a continuum of Indo-Iranian languages probably began to diverge by 2000 BC, if not earlier, preceding both the Vedic and Iranian cultures. The earliest recorded forms of these languages, Vedic Sanskrit and Gathic Avestan, are remarkably similar, descended from the common Proto–Indo-Iranian language. The origin and earliest relationship between the Nuristani languages and that of the Iranian and Indo-Aryan groups is complex.
Two-wave models of Indo-Iranian expansion have been proposed by and Parpola (1999). The Indo-Iranians and their expansion are strongly associated with the Proto-Indo-European invention of the chariot. It is assumed that this expansion spread from the Proto-Indo-European homeland north of the Caspian sea south to the Caucasus, Central Asia, the Iranian plateau, and Northern India. They also expanded into Mesopotamia and Syria and introduced the horse and chariot culture to this part of the world. Sumerian texts from EDIIIb Girsu (2500–2350 BC) already mention the 'chariot' (gigir) and Ur III texts (2150–2000 BC) mention the horse (anshe-zi-zi).
Linguistic remains can be found in a Hittite horse-training manual written by one "Kikkuli the Mitannian". Other evidence is found in references to the names of Mitanni rulers and the gods they swore by in treaties; these remains are found in the archives of the Mitanni's neighbors. The time period for this is about 1500 BC. In a treaty between the Hittites and the Mitanni, the deities Mitra, Varuna, Indra, and Nasatya (Ashvins) are invoked. Kikkuli's horse training text includes technical terms such as aika (eka, one), tera (tri, three), panza (pancha, five; compare with Gr. pente), satta (sapta, seven), na (nava, nine; compare with Lat. novem), vartana (vartana, turn, round in the horse race; compare with Lat. vertere, vortex). The numeral aika "one" is of particular importance because it places the superstrate in the vicinity of Indo-Aryan proper as opposed to Indo-Iranian or early Iranian (which has "aiva") in general.
The standard model for the entry of the Indo-European languages into South Asia is that this first wave went over the Hindu Kush, either into the headwaters of the Indus and later the Ganges. The earliest stratum of Vedic Sanskrit, preserved only in the Rigveda, is assigned to roughly 1500 BC. From the Indus, the Indo-Aryan languages spread from c. 1500 BC to c. 500 BC, over the northern and central parts of the subcontinent, sparing the extreme south. The Indo-Aryans in these areas established several powerful kingdoms and principalities in the region, from eastern Afghanistan to the doorstep of Bengal. The most powerful of these kingdoms were the post-Rigvedic Kuru (in Kurukshetra and the Delhi area) and their allies the Pañcālas further east, as well as Gandhara and later on, about the time of the Buddha, the kingdom of Kosala and the quickly expanding realm of Magadha. The latter lasted until the 4th century BC, when it was conquered by Chandragupta Maurya and formed the center of the Mauryan empire.
In eastern Afghanistan and southwestern Pakistan, whatever Indo-Aryan languages were spoken there were eventually pushed out by the Iranian languages. Most Indo-Aryan languages, however, were and still are prominent in the rest of the Indian subcontinent. Today, Indo-Aryan languages are spoken in India, Pakistan, Bangladesh, Nepal, Sri Lanka, Fiji and the Maldives.
The second wave is interpreted as the Iranian wave. The first Iranians to reach the Black Sea may have been the Cimmerians in the 8th century BC, although their linguistic affiliation is uncertain. They were followed by the Scythians, who are considered a western branch of the Central Asian Sakas. Sarmatian tribes, of whom the best known are the Roxolani (Rhoxolani), Iazyges (Jazyges) and the Alani (Alans), followed the Scythians westwards into Europe in the late centuries BCE and the 1st and 2nd centuries of the Common Era (The Age of Migrations). The populous Sarmatian tribe of the Massagetae, dwelling near the Caspian Sea, were known to the early rulers of Persia in the Achaemenid Period. At their greatest reported extent, around 1st century AD, the Sarmatian tribes ranged from the Vistula River to the mouth of the Danube and eastward to the Volga, bordering the shores of the Black and Caspian seas as well as the Caucasus to the south. In the east, the Saka occupied several areas in Xinjiang, from Khotan to Tumshuq.
The Medes, Parthians and Persians begin to appear on the Iranian plateau from c. 800 BC, and the Achaemenids replaced Elamite rule from 559 BC. Around the first millennium of the Common Era (AD), the Pashtuns and the Baloch began to settle on the eastern edge of the Iranian plateau, on the mountainous frontier of northwestern and western Pakistan, displacing the earlier Indo-Aryans from the area.
In Eastern Europe, the Iranians were eventually decisively assimilated (e.g. Slavicisation) and absorbed by the Proto-Slavic population of the region, while in Central Asia, the Turkic languages marginalized the Iranian languages as a result of the Turkic expansion of the early centuries AD. Extant major Iranian languages are Persian, Pashto, Kurdish, and Balochi besides numerous smaller ones. Ossetian, primarily spoken in North Ossetia and South Ossetia, is a direct descendant of Alanic, and by that the only surviving Sarmatian language of the once wide-ranging East Iranian dialect continuum that stretched from Eastern Europe to the eastern parts of Central Asia.
Archaeological cultures associated with Indo-Iranian expansion include:Europe
Poltavka culture (2700–2100 BC)
Andronovo horizon (2200–1000 BC)
Sintashta-Petrovka-Arkaim (2200–1600 BC),
Alakul (2100–1400 BC)
Fedorovo (1400–1200 BC)
Alekseyevka (1200–1000 BC)
Bactria-Margiana Archaeological Complex (2200–1700 BC)
Srubna culture (2000–1100 BC)
Abashevo culture (1700–1500 BC)
Yaz culture (1500–1100 BC)
India (middle Ganges plains)
Painted Gray Ware culture (1100–350 BC)
Early West Iranian Grey Ware (1500–1000 BC)
Late West Iranian Buff Ware (900–700 BC)
Swat culture (1600–500 BC)
Cemetery H culture (1900–1300 BC)
Parpola (1999) suggests the following identifications:
The Indo-European language spoken by the Indo-Iranians in the late 3rd millennium BC was a Satem language still not removed very far from the Proto–Indo-European language, and in turn only removed by a few centuries from the Vedic Sanskrit of the Rigveda. The main phonological change separating Proto–Indo-Iranian from Proto–Indo-European is the collapse of the ablauting vowels *e, *o, *a into a single vowel, Proto–Indo-Iranian *a (but see Brugmann's law). Grassmann's law and Bartholomae's law were also complete in Proto–Indo-Iranian, as well as the loss of the labiovelars (kw, etc.) to k, and the Eastern Indo-European (Satem) shift from palatized k' to ć, as in Proto–Indo-European *k'ṃto- > Indo-Iran. *ćata- > Sanskrit śata-, Old Iran. sata "100".
Among the sound changes from Proto–Indo-Iranian to Indo-Aryan is the loss of the voiced sibilant *z, among those to Iranian is the de-aspiration of the PIE voiced aspirates.
R1a1a (R-M17 or R-M198) is the sub-clade most commonly associated with Indo-European speakers. Most discussions purportedly of R1a origins are actually about the origins of the dominant R1a1a (R-M17 or R-M198) sub-clade. Data so far collected indicates that there are two widely separated areas of high frequency, one in South Asia, around North India, and the other in Eastern Europe, around Poland and Ukraine. The historical and prehistoric possible reasons for this are the subject of on-going discussion and attention amongst population geneticists and genetic genealogists, and are considered to be of potential interest to linguists and archaeologists also.
Out of 10 human male remains assigned to the Andronovo horizon from the Krasnoyarsk region, 9 possessed the R1a Y-chromosome haplogroup and one C-M130 haplogroup (xC3). mtDNA haplogroups of nine individuals assigned to the same Andronovo horizon and region were as follows: U4 (2 individuals), U2e, U5a1, Z, T1, T4, H, and K2b.
90% of the Bronze Age period mtDNA haplogroups were of west Eurasian origin and the study determined that at least 60% of the individuals overall (out of the 26 Bronze and Iron Age human remains' samples of the study that could be tested) had light hair and blue or green eyes.
A 2004 study also established that during the Bronze Age/Iron Age period, the majority of the population of Kazakhstan (part of the Andronovo culture during Bronze Age), was of west Eurasian origin (with mtDNA haplogroups such as U, H, HV, T, I and W), and that prior to the 13th–7th century BCE, all Kazakh samples belonged to European lineages.