How did the migrations of Indo-Aryan and Iranian speakers differ?

The original homeland of the Indo-Iranian language group is believed to have been located north of Afghanistan and east of the Caspian Sea, in a region encompassing parts of modern-day Turkmenistan, Uzbekistan, and Tajikistan. From this area, the two groups diverged in their migration patterns:1

• Indo-Aryan Migration: Indo-Aryan speakers migrated to the south and east, eventually settling in the northwest of the Indian subcontinent. This process is generally understood as a series of migrations rather than a single event, with entry into the subcontinent plausibly beginning in the early 2nd millennium BCE.1
• Iranian Migration: Iranian speakers migrated to the south and west. By the 1st millennium BCE, they were moving into western Iran from the east, likely following routes along the southern face of the Alborz Mountains. As they entered the Zagros Mountains, they spread northwest and southeast, gradually infiltrating areas held by indigenous populations.12

While the reasons for the initial split remain unknown, the linguistic evidence supports the thesis that Indo-Aryans moved to the subcontinent from an external homeland.1