With Peter Enns pushing the envelope, I assume it’s only a matter of time before the PCA (as well as the OPC, URCNA, &c.) has to decide where to draw the line. Thus far discussion tends to coalescence around the “historical Adam.” However, it’s important to keep in mind that that phrase is quite ambiguous.
In principle, someone could affirm the historicity of Adam without affirming that Adam and Eve were the first humans, or the progenitors of the human race. One tactic is to claim that God singled out a couple of Neolithic farmers.
Likewise, someone could affirm that Adam and Eve were the first humans without affirming that Adam and Even were the first hominids. In principle, someone could affirm that Adam and Eve were real people, consistent with an evolutionary history of early man. One tactic is to claim that God took two protohuman hominids and humanized them.
If, therefore, the PCA wishes to reaffirm the traditional understanding of Adam and Eve, it will need to use a narrower formulation than the “historical Adam.” It will have to add further qualifications to eliminate theistic evolution–if that’s its goal.