But like every historical entity, theories undergo change through time. Indeed a scientific theory might undergo such significant changes that the only point of continuing to name it after its source is to identify its lineage and ancestry. This is decidedly not the case with Darwinism.
From this description, the term "Darwinism" seems to have been arbitrarily and unnecessarily assigned, since the basic theory admittedly has not undergone any significant revision or divergence to make it necessary to designate or group the theories by lineage.
As a philosophical designation, it appears to be indistinguishable from philosophical naturalism, which again seems unnecessary, and potentially confusing and ambiguous.
“From this description, the term “Darwinism” seems to have been arbitrarily and unnecessarily assigned, since the basic theory admittedly has not undergone any significant revision or divergence to make it necessary to designate or group the theories by lineage.”
No, that’s certainly not true, since we in fact do label many of the revisions of the theory “neo-darwinian”, to distinguish them from the classical version of the theory. The source simply says that the theory hasn’t changed so much that the ONLY point to using the name is to connect it to its origin.
“As a philosophical designation, it appears to be indistinguishable from philosophical naturalism, which again seems unnecessary, and potentially confusing and ambiguous.”
No, naturalism is a much more general term. You could say that Darwinisim is a subset or outgrowth of philosophical naturalism, but the two terms are not synonymous.