Physical anthropologists propose the movement of at least two Caucasian physical types into the Tarim Basin. Mallory and Mair associate these types with the Tocharian and Iranian (Saka) branches of the Indo-European language family, respectively. However, archaeology and linguistics professor Elizabeth Wayland Barber cautions against assuming the mummies spoke Tocharian, noting a gap of about a thousand years between the mummies and the documented Tocharians: "people can change their language at will, without altering a single gene or freckle." confirm a second Caucasian physical type at Alwighul (700–1 BCE) and Krorän (200 CE) different from the earlier one found at Qäwrighul (1800 BCE) and Yanbulaq (1100–500 BCE). Mallory and Mair associate this later (700 BCE – 200 CE) Caucasian physical type with the populations who introduced the Iranian Saka language to the western part of the Tarim basin.