the meaning of "genetic relationship"

[Jacob Baltuch]

----------------------------Original message----------------------------
Isidore Dyen wrote:
 
>The reason interrelated languages are treated as wholes is that each
>represents a separate continuation of the original unitary language via a
>succession of native speakers, their separation occurring at the moment
>the last cross-pair of mutually intelligible speakers had vanished.
 
What do "native speakers" have to do in all of this? As far as I know
it is not likely that Latin developped into French "via a succession
of native speakers". If the first generation of Gauls who adopted Latin
did not have Latin nannies isn't it likely that the starting point of
French was a form of Latin spoken by non-native speakers? Then you've
got a break in the succession right there. Why worry about "speakers"
in the first place? I thought a linguistic relationship could be defined
as a relatioship between *systems* without worrying about the details of
the transmission.