You're confusing two issues:

1. Are today's Palestinians descendants of the Palestinians of Herodotus's day? DNA says yes.

2. Did Palestinians have a distinct Palestinian identity? History says the first clear signs of that were early in the 19th century.

You don't seem to think proportionality is relevant to fairness when dividing something. I do. The division happened in '47, so the plan should have reflected reality in '47.