I assume you mean that you postulate that they could "both be traced back to the same thing". Given that Darwin based his theory on empirical data of micro evolution (where organisms adapt to their environments without fundamentally altering their core characteristics), then there must be empirical evidence of the inter-genus leap required by macro evolution.
But, as the missing link is still missing, it is not possible to do such a traceback. A theory must live or die based on its founding evidence, and macro evolution cannot support itself without extrapolation of data that cannot be verified in accordance with its foundation.
Assuming I grant that to be true, mere absence of evidence is not itself evidence of absence. I can't help but think of the Soviet cosmonauts who, upon returning to earth, announced that there was no God - after all, if there were a God, they would have seen Him ;)