Re. Hagga munti

[Clem Lee <clem2@idt.net>]

Dear Mr. Liu Zinfad,

As stated by you:

3. My research is now focussing on Language change and shift in Southern
China, and I would like to share my findings with anyone of you. To sum
up: both Hakka and Modern Cantonese (and aslso most dialects in Jiangxi)
are the descendants of a common tongue coming from the northern central
plain. Old dialects in Guangdong have been displaced and creolized by
this strong dialect and are only found in the remoted areas like hilly
regions in Northern Guangdong. They are now referred to "Tuhua"
(Farmer's tongue).

My question: 

If "Hakka and Modern Cantonese (most dialects in Jiangxi)" originated
from "one common tongue", why are they so different sounding that a
Hakka, a Cantonese or someone from Jiangxi can't understand one another
if they use their own respective dialects to speak to one another?

The Hakkas and Cantonese have been neighbours for hundreds of years, is
it possible for them to change or evolve the "common tongue" of the
"northern central plain" so drastically so that they can't communicate
by speech using their respective dialect?

My question really is: 

How did all that happen? With all due respects, your theory sounds very
much like the Bible story of "the Tower of Babel" !!!

Clem Lee(Li)