This haplogroup gave me something to think about when I first got interested in the subject. I gave up, and thought ‘probably the Arabian peninsula’, as it didn’t seem widespread or varied enough in Africa to be indigenous, but was obviously very early in the migration out of Africa. Well, it looks more like the place of origin for M1 is India or Pakistan, and there has been a large population movement back into Africa from that direction.
This study provides evidence that M1, or its ancestor, had an Asiatic origin. The earliest M1 expansion into Africa occurred in northwestern instead of northeastern areas; this early spread reached the Iberian Peninsula even affecting the Basques. The majority of the M1a lineages found outside and inside Africa had a more recent eastern Africa origin. Both western and eastern M1 lineages participated in the Neolithic colonization of the Sahara. The striking parallelism between subclade ages and geographic distribution of M1 and its North African U6 counterpart strongly reinforces this scenario. Finally, a relevant fraction of M1a lineages present today in the European Continent and nearby islands possibly had a Jewish instead of the commonly proposed Arab/Berber maternal ascendance.
I will give time to the theory that there was a relatively advanced Indus Valley Civilisation at that time, and this may have been what caused the Westward population movement. There’s some evidence (but not proof) that there was pottery and city building during the ice age there, and this means farming. And farmers displace hunter gatherers the world over. You’d have to study the age of the domesticated crops in India and Pakistan to check this without a lot of deep diving into the Bay of Bengal.