The concept derives from the notion that the original speakers of the Indo-European languages and their descendants up to the present day constitute a distinctive race or subrace of the Caucasian race.
The term Aryan has generally been used to describe the Proto-Indo-Iranian language root *arya which was the ethnonym the Indo-Iranians adopted to describe Aryans. Its cognate in Sanskrit is the word ārya (Devanāgarī: आर्य), in origin an ethnic self-designation, in Classical Sanskrit meaning "honourable, respectable, noble". The Old Persian cognate ariya- (Old Persian cuneiform: 𐎠𐎼𐎡𐎹) is the ancestor of the modern name of Iran and ethnonym for the Iranian people.
The term Indo-Aryan is still commonly used to describe the Indic half of the Indo-Iranian languages, i.e., the family that includes Sanskrit and modern languages such as Hindi-Urdu, Bengali, Nepali, Punjabi, Gujarati, Romani, Kashmiri, Sinhala and Marathi.
In the 18th century, the most ancient known Indo-European languages were those of the ancient Indo-Iranians. The word Aryan was therefore adopted to refer not only to the Indo-Iranian peoples, but also to native Indo-European speakers as a whole, including the Romans, Greeks, and the Germanic peoples. It was soon recognised that Balts, Celts, and Slavs also belonged to the same group. It was argued that all of these languages originated from a common root – now known as Proto-Indo-European – spoken by an ancient people who were thought of as ancestors of the European, Iranian, and Indo-Aryan peoples.
In the context of 19th-century physical anthropology and scientific racism, the term "Aryan race" came to be misapplied to all people descended from the Proto-Indo-Europeans – a subgroup of the Europid or "Caucasian" race, in addition to the Indo-Iranians (who are the only people known to have used Arya as an endonym in ancient times). This usage was considered to include most modern inhabitants of Australasia, the Caucasus, Central Asia, Europe, Latin America, North America, Siberia, South Asia, Southern Africa, and West Asia. Such claims became increasingly common during the early 19th century, when it was commonly believed that the Aryans originated in the south-west Eurasian steppes (present-day Russia and Ukraine).
Max Müller is often identified as the first writer to mention an "Aryan race" in English. In his Lectures on the Science of Language (1861), Muller referred to Aryans as a "race of people". At the time, the term race had the meaning of "a group of tribes or peoples, an ethnic group". He occasionally used the term "Aryan race" afterwards,  but wrote in 1888 that "an ethnologist who speaks of Aryan race, Aryan blood, Aryan eyes and hair, is as great a sinner as a linguist who speaks of a dolichocephalic dictionary or a brachycephalic grammar";
While the "Aryan race" theory remained popular, particularly in Germany, some authors opposed it, in particular Otto Schrader, Rudolph von Jhering and the ethnologist Robert Hartmann (1831–1893), who proposed to ban the notion of "Aryan" from anthropology.
Müller's concept of Aryan was later construed to imply a biologically distinct sub-group of humanity, by writers such as Arthur de Gobineau, who argued that the Aryans represented a superior branch of humanity. Müller objected to the mixing of linguistics and anthropology. "These two sciences, the Science of Language and the Science of Man, cannot, at least for the present, be kept too much asunder; [...] I must repeat, what I have said many times before, it would be as wrong to speak of Aryan blood as of dolichocephalic grammar". He restated his opposition to this method in 1888 in his essay Biographies of words and the home of the Aryas.
By the late 19th century the steppe theory of Indo-European origins was challenged by a view that the Indo-Europeans originated in ancient Germany or Scandinavia – or at least that in those countries the original Indo-European ethnicity had been preserved. The word Aryan was consequently used even more restrictively – and even less in keeping with its Indo-Iranian origins – to mean "Germanic", "Nordic" or Northern Europeans. This implied division of Caucasoids into Aryans, Semites and Hamites was also based on linguistics, rather than based on physical anthropology; it paralleled an archaic tripartite division in anthropology between "Nordic", "Alpine" and "Mediterranean" races. The German origin of the Aryans was especially promoted by the archaeologist Gustaf Kossinna, who claimed that the Proto-Indo-European peoples were identical to the Corded Ware culture of Neolithic Germany. This idea was widely circulated in both intellectual and popular culture by the early twentieth century, and is reflected in the concept of "Corded-Nordics" in Carleton S. Coon's 1939 The Races of Europe.
This usage was common among knowledgeable authors writing in the late 19th and early 20th centuries. An example of this usage appears in The Outline of History, a bestselling 1920 work by H. G. Wells. In that influential volume, Wells used the term in the plural ("the Aryan peoples"), but he was a staunch opponent of the racist and politically motivated exploitation of the singular term ("the Aryan people") by earlier authors like Houston Stewart Chamberlain and was careful either to avoid the generic singular, though he did refer now and again in the singular to some specific "Aryan people" (e.g., the Scythians). In 1922, in A Short History of the World, Wells depicted a highly diverse group of various "Aryan peoples" learning "methods of civilization" and then, by means of different uncoordinated movements that Wells believed were part of a larger dialectical rhythm of conflict between settled civilizations and nomadic invaders that also encompassed Aegean and Mongol peoples inter alia, "subjugat[ing]" – "in form" but not in "ideas and methods" – "the whole ancient world, Semitic, Aegean and Egyptian alike".
In the 1944 edition of Rand McNally's World Atlas, the Aryan race is depicted as one of the ten major racial groupings of mankind. The science fiction author Poul Anderson, an anti-racist libertarian of Scandinavian ancestry, in his many works, consistently used the term Aryan as a synonym for "Indo-Europeans".
The use of "Aryan" as a synonym for Indo -European may occasionally appear in material that is based on historic scholarship. Thus, a 1989 article in Scientific American, Colin Renfrew uses the term "Aryan" as a synonym for "Indo-European".
- "The Great Aryan Myth," Knight Dunlap, The Scientific MonthlyVol. 59, No. 4 (Oct., 1944), pp. 296-300
- Mish, Frederic C., Editor in Chief Webster's Tenth New Collegiate Dictionary Springfield, Massachusetts, U.S.A.:1994--Merriam-Webster See original definition (definition #1) of "Aryan" in English--Page 66
- "Devdutt Pattanaik: Leveraging the Aryans". 2016-03-27.
- Monier-Williams (1899).
- "Monier Williams Sanskrit-English Dictionary (2008 revision)". UNIVERSITÄT ZU KÖLN. Retrieved July 25, 2010.
- Bailey, H.W. "Arya". Encyclopædia Iranica. Retrieved April 21, 2018.
- Fortson, Benjamin W. Indo-European Language and Culture: An Introduction. 2nd ed., Wiley-Blackwell, 2010, paras. 10.28 and 10.58.
- Mish, Frederic C., Editor in Chief Webster's Tenth New Collegiate Dictionary Springfield, Massachusetts, U.S.A.:1994--Merriam-Webster Page 66
- Widney, Joseph P Race Life of the Aryan Peoples New York: Funk & Wagnalls. 1907 In Two Volumes: Volume One--The Old World Volume Two--The New World ISBN B000859S6O
- Rand McNally's World Atlas International Edition Chicago:1944 Rand McNally Map: "Races of Mankind" pp. 278–279.
- Andrea Orsucci, "Ariani, indogermani, stirpi mediterranee: aspetti del dibattito sulle razze europee (1870-1914) Archived 2002-03-10 at the Wayback Machine", in Cromohs, 1998 (in Italian)
- OED under race, n.6 I.1.c has "A group of several tribes or peoples, regarded as forming a distinct ethnic set. Esp. used in 19th-cent. anthropological classification, sometimes in conjunction with linguistic groupings."
- Romila Thapar, "The Theory of Aryan Race and India: History and Politics," Social Scientist 24.1/3 (Jan.–Mar. 1996), 6. Thapar cites an 1883 lecture in which Mueller spoke of someone as "belonging to the south-eastern branch of the Aryan race."
- F. Max Müller, Biographies of Words and the Home of the Aryas (1888), Kessinger Publishing reprint, 2004, p. 120; Dorothy Matilda Figueira, Aryans, Jews, Brahmins: Theorizing Authority Through Myths of Identity (SUNY Press, 2002), p. 45.
- Speech before the University of Stassbourg, 1872, Chaudhuri, Nirad, Scholar Extraordinary: The Life of Professor the Rt. Hon. Friedrich Max Muller, Chatto and Windus, 1974, p.313
- Vacher de Lapouge (trans Clossen, C), Georges (1899). "Old and New Aspects of the Aryan Question". The American Journal of Sociology. 5 (3): 329–346. doi:10.1086/210895.
- Arvidsson, Stefan (2006). Aryan Idols. USA: University of Chicago Press, 143. ISBN 0-226-02860-7.
- Wells, H.G. The Outline of History, 3rd ed. (New York: Macmillan, 1921), Ch. 20 ("The Aryan-Speaking Peoples in Prehistoric Times"), pp. 236-51.
- "H.G. Wells in 1922 on the early history of "the Aryan peoples" (Proto-Indo Europeans)". bartleby.com. Retrieved August 16, 2015.
- Rand McNally (1944) "Races of Mankind" (map)Rand McNally's World Atlas International Edition Chicago: Rand McNally. pp.278–79 – In the explanatory section below the map, the Aryan race (the word "Aryan" being defined in the description below the map as a synonym for "Indo-Europeans") is described as being one of the ten major racial groupings of mankind. Each of the ten racial groupings is depicted in a different color on the map and the estimated populations in 1944 of the larger racial groups except the Dravidians are given (the Dravidian population in 1944 would have been about 70,000,000). The other nine groups are depicted as being the Semitic race (the Aryans (850,000,000) and the Semites (70,000,000) are described as being the two main branches of the Caucasian race), the Dravidian race, the Mongolian race (700,000,000), the Malayan race (Correct population given on page 413 – 64,000,000 including besides the populations of the Dutch East Indies, the Philippines, and Madagascar also half of the Malay States, Micronesia, and Polynesia), the American Indian race (10,000,000), the Negro race (140,000,000), the Native Australians, the Papuans, and the Hottentots and Bushmen.
- See, for example, the Poul Anderson short stories in the 1964 collection Time and Stars and the Polesotechnic League stories featuring Nicholas van Rijn
- Renfrew, Colin. (1989). The Origins of Indo-European Languages. /Scientific American/, 261(4), 82-90.
- Widney, Joseph P Race Life of the Aryan Peoples New York: Funk & Wagnalls. 1907 In Two Volumes: Volume One--The Old World Volume Two--The New World ISBN B000859S6O: