Razib Khan, at the Brown Pundits group blog, calls attention to a July 2019 paper in Science demonstrating with ancient cattle mtDNA that there was surge of South Asian domesticated cattle from the Indus River Valley civilization into the Near East in the Bronze Age ca. 4000 to 3500 years ago. Before that time period only European cattle were present in the Near East.
This was probably in response to the civilization crushing drought that his both regions simultaneously around 2200 BCE to 2000 BCE, and ultimately led to the collapse of the Akkadian Empire in the Near East, to the collapse of an Egyptian dynasty, and to the collapse of the Harappan civilization in the Indus River Valley (including the demise of a river system at the heart of the Rig Vedic epics). This climate event was also probably a pivotal trigger for Indo-European expansion, creating a vacuum of collapsed civilizations into which a culture from the steppe which was better adapted to these conditions could and did expand.
This paper shows South Asian-Near East contracts that pervasively influenced daily life in the Near East despite the fact that Indo-European subculture, the Indo-Aryans (i.e. the Sanskrit speaking population that became dominant in much of South Asia in the Bronze Age, and had an even broader and ore lasting religious impact), left only a short term cultural and linguistic impact in the Near East, and didn't leave much of a demic (i.e. population genetic) impact in the Near East either.
The interesting aspect of cattle is that there are really two species that intermix. Using mtDNA researchers estimate indicus and taurus diverged 300,000 to 2,000,000 years ago. . . . Ancient cattle from the Near East are all taurus. . . . [But] there is a massive jump in genome-wide indicus ancestry across the Near East between 2000 and 1500 BC. As the authors note this can’t be diffusion; the jump is too sudden and sweeping.So what happened during this period? As noted in the paper: Bronze Age civilization almost collapsed around ~2000 BC. More concretely, after 2000 BC is when we see evidence of Indo-Europeans in the Near East. The Indo-Aryan Mittani show up in Mesopotamia in ~1600 BC. The Indo-European Hittites, the Nesa, are known from Anatolia a bit earlier. This is also the period that small, but detectable, levels of “steppe” ancestry show up in some ancient samples.Before this paper, I would have leaned to the position that the Mittani Indo-Aryans migrated directly from the Sintashta homeland without much contact with Indian Indo-Aryans.
These data are too suggestive of a widespread zone of expanding agro-pastoralists that existed between western South Asia and the Near East between 2000 BC and 1500 BC. . . . Aside from the Mittani the evidence of Indo-Aryans in the Near East is tenuous, though some of the Kassites of Babylonia may have had Indo-European affinities. There is not nearly as strong a genetic imprint of steppe in the Fertile Crescent as in Northwest India.
The Hittites were very different from Indo-Aryans, who seem to have the closest relationship to the Slavic language family.The indicus breed is adapted to tropical dry climates. It seems plausible that the Indo-Aryan[s] . . . facilitated the spread of this breed in the centuries before 1500 BC.