The Azerbaijanis or Azeris are a Turkic ethnic group of mixed ethnic origins, primarily the indigenous peoples of eastern Transcaucasia, the Medians, an ancient Iranian people, and the Oghuz Turkic tribes that began migrating to Azerbaijan in the 11th century CE. Modern Azerbaijanis are the second most numerous ethnic group among the Turkic peoples after Anatolian Turks and speak North Azerbaijani (spoken mainly in the Republic of Azerbaijan and Russia) and/or South Azerbaijani (spoken in Iran, Iraq, and Syria). Both languages also have dialects, with 21 North Azerbaijani dialects and 11 South Azerbaijani dialects.

The Azerbaijani are of mixed ethnic origin, the oldest element deriving from the indigenous population of eastern Transcaucasia and possibly from the Medians of northern Persia. Between the 3rd and 7th centuries CE, there was a Persianization of the population, during the period of the Sassanian dynasty. A subsequent Turkification of the population occurred after the region's conquest by the Seljuq Turks in the 11th century and a continued influx of Turkic peoples over subsequent centuries – including groups that migrated during the Mongol conquests of the 13th century (most of the tribes that formed the Mongol forces, or were led by them to migrate were Turkic peoples.)"Azerbaijani" – Encyclopædia Britannica

Caucasian substrate The Caucasian origin of the Azerbaijanis defines a link between Azerbaijanis and their pre-Turkification Caucasian past and mostly applies to the Azerbaijanis of the Caucasus, most of whom are now inhabitants of what is now the Republic of Azerbaijan. There is evidence that, due to repeated invasions and migrations, aboriginal Caucasians were culturally assimilated, first by Iranians, such as the Alans, and later by the Oghuz Turks. Considerable information has been learned about the Caucasian Albanians including their language, history, early conversion to Christianity, and close ties to the Armenians. Many academics believe that the Udi language, still spoken in Azerbaijan, is a remnant of the Albanians' language."The Udi Language" , Ludwig-Maximilians-Universität München, Wolfgang Schulze 2001/2 (retrieved 19 June 2006).

This Caucasian influence extended further south into Iranian Azerbaijan. During the 1st millennium BCE, another Caucasian people, the Mannaeans (Mannai) populated much of this area. This ancient country was in northwestern Iran, south of Lake Urmia. During the period of its existence in the early 1st millennium BCE, Mannai was surrounded by three major powers: Assyria, Urartu, and Media. With the intrusion of the Scythians and the rise of the Medes in the 7th century, the Manneans lost their identity and were subsumed under the term Medes."Mannai", Encyclopædia Britannica (retrieved 7 September 2011).

Genetic testing

Although genetic testing demonstrates that the genetic heritage of Azerbaijani Turks is mostly from the native populations of the Middle East and the Caucasus, rather than their being direct descendants of migrants from Central Asia, it does, however, show that the region is a genetically mixed one. Whereas the population of Azerbaijan is culturally diverse, genetic testing has revealed common genetic markers that support an autochthonous (indigenous) background for most Azerbaijani Turks. MtDNA analysis indicates that the main relationship with Iranians is through a larger West Eurasian group that is secondary to that of the Caucasus, according to a study that did not include Azerbaijani Turks, but Georgians who have clustered with Azerbaijani Turks in other studies.Where West Meets East: The Complex mtDNA Landscape of the Southwest and Central Asian Corridor – American Journal of Human Genetics, 74:827-845, 2004 (retrieved 9 June 2006) The conclusion from the testing shows that Azerbaijani Turks of the republic are a mixed population with relationships, in order of greatest similarity, with the Caucasus, Iranians and Near Easterners, Europeans, and Turkmen. Other genetic analysis of mtDNA (maternal) and Y-chromosomes (paternal) indicates that Caucasian populations are genetically intermediate between Europeans and Near Easterners, but that they are more closely related to Near Easterners overall. Another study, conducted in 2003 by the Russian Journal of Genetics, compared Iranian-language speakers of the Republic of Azerbaijan (the Talysh and Tats) with Turkic Azerbaijanis and found that the genetic structure of those populations, compared with the other Iranian-speaking populations (Persians from Iran, Ossetins, and Tajiks), was closer to Turkic Azerbaijanis than to Iranian-speaking populations elsewhere.Genetic Structure of Iranian-Speaking Populations from Azerbaijan Inferred from the Frequencies of Immunological and Biochemical Gene Markers – Russian Journal of Genetics, Volume 39, Number 11, November 2003, pp. 1334-1342(9) (retrieved 9 June 2006)

In 2006, M. Regueiro and A.M. Cadenas of Stanford University showed that the population of central Iran (Isfahan) was closer to Caucasian Azerbaijani people than to the population of Turkey in terms of haplogroup distributions and genetic homogeneity.Iran: Tricontinental Nexus for Y-Chromosome Driven Migration – Hum Hered 2006;61:132–143 (retrieved 13 April 2011)

The latest comparative study (2013) on the complete mitochondrial DNA diversity in Iranians has indicated that Iranian Azerbaijanis are more related to the people of Georgia than they are to other Iranians and to Armenians. However, the same multidimensional scaling plot shows that Azerbaijanis from the Caucasus, despite their supposed common origin with Iranian Azerbaijanis, cluster closer with other Iranians (e.g. Persians, etc.) than they do with Iranian Azerbaijanis.

Azerbaijani Turks, however, are still demonstrated to possess significant genetic influences from East Asia relative to their non-Turkic neighbors.

Iranian substrate The Iranian origin of the Azerbaijanis defines a link between present-day Azerbaijanis and their Azari past and mostly applies to Iranian Azerbaijanis. Although the Azeri people are known to be Turkic, their ancestral roots go back to Indo-Iranian tribes and ethnic groups. It is supported by historical accounts, by the existence of the Old Azari language, present-day place names, cultural similarities between Iranian peoples and Azerbaijanis, and archaeological and ethnical evidence. It is also favored by notable scholars and sources, such as Vladimir Minorsky, Richard Frye, Xavier De Planhol, Encyclopaedia of Islam, Encyclopædia Iranica, Encyclopædia Britannica, Grand Dictionnaire Encyclopedique Larousse, and World Book Encyclopedia.

Historical accounts and the ancient Azari language

According to Vladimir Minorsky, around the 9th and 10th centuries:

Professor Ighrar Aliyev also mentions that the Arab historians Baladhuri, Masudi, Ibn Hawqal and Yaqut have mentioned this language by name.Professor Ighrar Aliyev. The History of Aturpatakan. Persian Translation by Dr. Shaadman Yusuf. Balkh Publishers. Tehran. 1999. Medieval historians and scholars also record the people of the region of Azerbaijan as Iranians who spoke Iranian languages. Among these are Al-Istakhri, Al-Masudi, Ibn al-Nadim, Hamzeh Esfahani, Ibn Hawqal, Al-Baladhuri, Moqaddasi, Yaghubi, Hamdallah Mostowfi, and Al-Khwarizmi.

Ebn al-Moqaffa' (d. 142/759) is quoted by ibn Al-Nadim in his famous Al-Fihrist as stating that Azerbaijan, Nahavand, Rayy, Hamadan and Esfahan speak Pahlavi (Fahlavi) and collectively constitute the region of Fahlah.Ibn Nadeem, "Fihrist", Translated by Reza Tajaddod, Ibn Sina publishers, 1967. ابن نديم در الفهرست مي‌نويسد: (= اما فهلوي منسوب است به فهله كه نام نهاده شده است بر پنج شهر: اصفهان و ري و همدان و ماه نهاوند و آذربايجان. و دري لغت شهرهاي مداين است و درباريان پادشاه بدان زبان سخن مي‌گفتند و منسوب است به مردم دربار و لغت اهل خراسان و مشرق و لغت مردم بلخ بر آن زبان غالب است. اما فارسي كلامي است كه موبدان و علما و مانند ايشان بدان سخن گويند و آن زبان مردم اهل فارس باشد. اما خوزي زباني است كه ملوك و اشراف در خلوت و مواضع لعب و لذت با نديمان و حاشيت خود گفت‌وگو كنند. اما سرياني آن است كه مردم سواد بدان سخن رانند). ابن ندیم، محمد بن اسحاق: «فهرست»، ترجمه‌ي رضا تجدد، انتشارات ابن سینا، 1346

فأما الفهلوية فمنسوب إلى فهله اسم يقع على خمسة بلدان وهي أصفهان والري وهمدان وماه نهاوند وأذربيجان وأما الدرية فلغة مدن المدائن وبها كان يتكلم من بباب الملك وهي منسوبة إلى حاضرة الباب والغالب عليها من لغة أهل خراسان والمشرق و اللغة أهل بلخ وأما الفارسية فتكلم بها الموابدة والعلماء وأشباههم وهي لغة أهل فارس وأما الخوزية فبها كان يتكلم الملوك والأشراف في الخلوة ومواضع اللعب واللذة ومع الحاشية وأما السريانية فكان يتكلم بها أهل السواد والمكاتبة في نوع من اللغة بالسرياني فارسي [Original Arabic]; Ibn Nadeem, Al-Fihrist. www.alwaraq.com accessed in September 2007.

A very similar statement is given by the medieval historian Hamzeh Isfahani when talking about Sassanid Iran. Hamzeh Isfahani writes in the book Al-Tanbih 'ala Hoduth alTashif that five "tongues" or dialects, were common in Sassanian Iran: Pahlavi (Fahlavi), Dari, Parsi (Farsi), Khuzi and Soryani. Hamzeh (893-961 A.D.) explains these dialects in the following way:

Ibn Hawqal mentions that some areas of Armenia are controlled by Muslims and others by Christians.Ibn Howqal, Surat al-ardh. Translation and comments by: J. Shoar, Amir Kabir Publishers, Iran. 1981. "ارمنیه دو قسمت است: داخلی و خارجی در ارمنیه ی خارجی شهرهایی از آن مسلمانان و به دست آنان است و خود مسلمانان فرمانروای آنجا هستند و دست ارامنه از دست آن قطع گردیده است و به کلی تحت حکومت پادشاهان اسلامی است: از جمله این شهرها ارجیش، منازجرد و خلاط است. و حدود ارمنیه خارجی معین است یعنی از مشرق به بردعه و از مغرب به جزیره و از جنوب به آذربایجان و از شما به نواحی روم در سمت قالیقالا محدود است

Al-Moqaddasi (died late 4th century AH/10th century CE) considers Azerbaijan as part of the 8th division of lands. He states: "The languages of the 8th division is Iranian (al-'ajamyya). It is partly Dari and partly convoluted (monqaleq) and all of them are named Persian".Al-Moqaddasi, Shams ad-Din Abu Abdallah Muhammad ibn Ahmad, Ahsan al-Taqasi fi Ma'rifa al-Aqalim, Translated by Ali Naqi Vaziri, Volume one, First Edition, Mu'alifan and Mutarjiman Publishers, Iran, 1981, p 377 المقدسي، شمس‌الدين ابوعبدالله محمدبن احمد، احسن التقاسيم في معرفه الاقاليم، ترجمه دكتر علينقي وزيري، جلد 1، چاپ اول، انتشارات مؤلفان و مترجمان ايران، 1361، ص 377.

Al-Moqaddasi also writes on the general region of Armenia, Arran and Azerbaijan. Ahmad ibn Yaqubi mentions that the "People of Azerbaijan are a mixture of 'Ajam-i Azari (Ajam is a term that developed to mean Iranian) of Azaris and old Javedanis (followers of Javidan the son of Shahrak who was the leader of Khurramites and succeeded by Babak Khorramdin)."(Tārīkh-i Yaqūbī / talīf-i Aḥmad ibn Abī Yaqūbi; tarjamah-i Muḥammad Ibrahim Ayati, Intirisharat Bungah-I Tarjamah va Nashr-I Kitab, 1969.

Zakarrya b. Moháammad Qazvini's report in Athar al-Bilad, composed in 674/1275, that "no town has escaped being taken over by the Turks except Tabriz" (Beirut ed., 1960, p. 339) one may infer that at least Tabriz had remained aloof from the influence of Turkish until the time. (Encyclopædia Iranica by E. Yarshater)

From the time of the Mongol invasion, most of whose armies were composed of Turkic tribes, the influence of Turkish increased in the region. On the other hand, the old Iranian dialects remained prevalent in major cities. Hamdallah Mostawafi writing in the 1340s calls the language of Maraqa as "modified Pahlavi"(Pahlavi-ye Mughayyar). Mostowafi calls the language of Zanjan (Pahlavi-ye Raast). The language of Gushtaspi covering the Caspian border region between Gilan to Shirvan is called a Pahlavi language close to the language of Gilan.«مستوفي، حمدالله: «نزهةالقلوب، به كوشش محمد دبيرسياقي، انتشارات طهوري، 1336 Mostawafi, Hamdallah. Nozhat al-Qolub. Edit by Muhammad Dabir Sayyaqi. Tahuri publishers, 1957.