In addition to this... Sure, evolution modifies existing structures, but if you compare a cat's heart and stomach to a pig heart and stomach, the difference is not that big, even though the nearest evolutionary ancestor was tens (hundreds?) of millions of years ago. Once a structure is in place and works well, you can certainly tweak it, but it's easier to mostly just keep it.

Humans have a neocortex, but if you play with a cat or dog, you can recognize and understand the emotions they are feeling. Fear, anger, joy, anxiety, relaxation, etc. That suggests the structures responsible for those things in us are probably not that different from them.