> The further back you go in Indo-European languages, they don't have articles.

Heh, while we're discussing English, this annoys me.

"The further back you go" is a continuum, the effect you describe should be too.

> The further back you go, the fewer Indo-European languages have articles.

Or match a discontinuity with a discontinuity.

> If you go back beyond a certain point, Indo-European languages don't have articles.