Why do a lot of Mexicans often score some Asia Central on AncestryDNA?

[shazou]

I've heard that it often reaches as high as 9% for some Mexicans, this 'Asia Central' category on AncestryDNA that is. Why does this happen?

http://dna.ancestry.com/ethnicity/central-asian

[Sikeliot]

Affinity to Mongolia via Amerindian DNA.

[rocky]

I didn't score any Central Asian, If they do it's probably from the Amerindian.

[jpb]

I am predominantly European with some NA ancestors. My results were 98% European and 2% Middle Eastern. Some people will say the Middle Eastern is NA, but I think it is related to my Eastern European. My great aunt on the side with the NA ancestors got a trace of Central Asian, which I believe is a signal to our Native Ancestor. I am 1/512; she is 1/128.