In any case, M73 would be a pre-Indo-European branch of R1b, just like V88 and M335.R1b-M269 (the most common form in Europe) is closely associated with the diffusion of Indo-European languages, as attested by its presence in all regions of the world where Indo-European languages were spoken in ancient times, from the Atlantic coast of Europe to the Indian subcontinent, which comprised almost all Europe (except Finland, Sardinia and Bosnia-Herzegovina), Anatolia, Armenia, European Russia, southern Siberia, many pockets around Central Asia (notably in Xinjiang, Turkmenistan, Tajikistan and Afghanistan), without forgetting Iran, Pakistan, northern India and Nepal.But the most compelling evidence that R1b people related to modern Europeans once roamed the Sahara is to be found at Tassili n'Ajjer in southern Algeria, a site famous pyroglyphs (rock art) dating from the Neolithic era.Some painting dating from around 3000 BCE depict fair-skinned and blond or auburn haired women riding on cows.The three main branches of R1b1 (R1b1a, R1b1b, R1b1c) all seem to have stemmed from the Middle East.The southern branch, R1b1c (V88), is found mostly in the Levant and Africa.Autosomally this Paleolithic population appears to have contributed mostly to the ancestry of modern Europeans and South Asians, the two regions where haplogroup R also happens to be the most common nowadays (R1b in Western Europe, R1a in Eastern Europe, Central and South Asia, and R2 in South Asia).
R1b tribes descended from mammoth hunters, and when mammoths went extinct, they started hunting other large game such as bisons and aurochs.
This is presumably the area from which R1b lineages started expanding - or in other words the "original homeland" of R1b.
The early R1b cattle herders would have split in at least three groups.
They split into two factions: R1b1a1 (M73), which went east along the Caspian Sea to Central Asia, and R1b1a2 (M269), which at first remained in the North Caucasus and the Pontic Steppe between the Dnieper and the Volga.
It is not yet clear whether M73 actually migrated across the Caucasus and reached Central Asia via Kazakhstan, or if it went south through Iran and Turkmenistan.