"Harping on common descent"?
Well I agree. It is the "tactic" of debating the relevant issues!
I have blogged on this before:
Biological evolution: What is being debated
It is deceitful to present evidence of bacteria "evolving" into bacteria, trilobites "evolving" into trilobites, and finches "evolving" into finches when as evidence for evolution #6. Especially when we don't understand the mechanism(s) by which that "evolution" took/ takes place.
True we can pretty much say that nature selects for certain size beaks under specific environmental pressures. However the origin of the variation is a mystery, as is the origin of the finch. To clarify- was the variation part of a built-in response to environmental cues- or was it the result of undirected, random mutations?
The mutation rate of bacteria increases under certain pressures- is this a sign of cellular intelligence searching for a solution? Or is it blind chance?
As for the trilobite lineage- Using bones only I am sure we could construct a "lineage" from chihuahua to Great Dane.
So yes, I "harp" on common descent because objective people should. People interested in the reality to our existence should. I take it that is why evolutionists do not. Oh well...