And yet…it’s simply not. It’s true that understanding the full range of forms something could adapt into, what mutations might make possible, is complex because genetics and developmental biology are complex. Nothing in biology is tidy. But you don’t need to understand all the particulars of astrophysics to get what stars are, and evolution as a general process is much more obvious than you are giving credit.
Something Darwin drew a lot of inspiration from was the work of breeders, who have reshaped plants and animals in very significant ways - nobody who saw a chihuahua unprepared would guess it was a wolf, or even closer to one than a fox. These changes are not invisible and not all ineffable, but many were and are done in a deliberate way.
The basic idea, then, is simply that the changes in nature might come from the same sort of thing happening on a grand scale. That much hardly seems difficult to grasp, and for anyone curious enough to look further, there are all sorts of signs of it even on the timescale of a human life. It’s just that some people don’t, and I don’t see how complexities like spandrels offer any real excuse.
