I found the argument only convincing for “preaching to the choir”, so to speak. as one already sympathetic to ID, it is obvious to me that the author does not adequately understand the concept, argument, or perspective of the “common design” argument, and thus, however unwittingly, the author confuses or misrepresents the argument at hand.
In the first case, for instance, the author observes
It seems that a human designer would have borrowed more directly from the bird body plan in designing bats, and from the fish skeleton in designing whales and dolphins.
No, no, and no. This is borne out if one considers either biology or mechanical engineering. a designer typically starts with a template, and modifies the original template in those ways that are most conducive to achieving the final ends.
If I had started with a basic mammal, and wanted to make a flying mammal… would anyone really want to suggest that it is easier, or more direct, to somehow import a bird’s wing a somehow paste that into a mammal rather than simply modifying a mammal’s forearm into a wing? a bird’s wing is fine tuned to the avionics, weight, etc., of a bird, not a mammal. if we he were to try to import the design of a bird’s wing onto a mammal to make a flying mammal, one would need to redesign practically everything about said mammal… bone structure, leg structure, weight, cardiovascular system, etc. etc.
Same would be true of whales… if a genetic engineer, even today if we had the knowledge and technology, wanted to develop an aquatic mammal, what would even a human engineer today do? Take a fish, keep those same fine and scales, and then do the massive redesign involved in giving it mammalian kings, fat, blubber, reproductive system, etc., etc., etc…
or take a mammal and make some (relatively) smaller and more minor modifications regarding location of blowhole, shape of limbs, etc.
I’m afraid that however well intentioned, this argument ends up being an unwitting straw man fallacy, only likely to convince the choir.