He is Seriously Confused
Evolution can be confusing, and this dog has a lot of questions. The first comedic element is the image of a chilled-out golden retriever with a shotgun, beer, and a camouflage hat. It gets even more humorous when you read the meme.
The dog’s chain of thought is that if they descended from wolves, then how come not all wolves evolved into dogs? Of course, there is a scientific explanation, but you tell that to the southern dog.