usually the only way to scientifically prove the genetic relationship of languages is to compare their grammar and lexicon on the earlier stages of development

I've read enough about genetic anthropology and linguistics to know that the aboriginal inhabitants of the American continents were almost certainly descendants of asians. Not only linguistic, but genetic evidence proves this.

It has been proven that all people originated from Africa that should be proof enough. http://www.pbs.org/wgbh/nova/transcripts/2120glang.html