For context, this man is a prominent geneticist frequently commenting on matters pertaining to our field. The ‘Maryannu’ he references here are a rather intriguing group spoken of in the ancient Near East, that appear to have constituted chariot-borne warriors. Indo-European chariot-borne warriors, based around the speculated etymological link of “Maryannu” to Sanskrit मर्य [‘Marya’] – a term which connoted young men, eager for glory.
The supposition is that, in line with very recent advancements in archaeology and archaeogenetics, the spread of these ‘Maryannu’ and their revolutionary chariot-borne warfare approach was an expansion of the Indo-Iranian, and more specifically Indo-Aryan clades coming down and heading *west* through the Near East. If you have read about the intriguing either Indo-Aryan or Sanskrit superstrate of Mitanni (an otherwise theoretically non-IE-base population that mysteriously seems to wind up with a ruling class speaking Indo-Aryan, utilizing Indo-Aryan deifics in their state religion, and employing horse-trainers that appear to have been quite directly linked to the Indo-Aryan civilization found further East … in fact with the entire confederacy built around such a corps) …
Well, the Maryannu are those guys, we suspect.
Khan is, of course, memeing quite hard about this. Yet all the best memes – they endure, precisely because they maintain an essence of truth.