Molly, our beloved Labrador retriever, certainly loved to eat poop. Sometimes she would chow down on her own feces, and at other times, she preferred excrement of the cows that lived behind our house. Mary Jean and I found this practice (coprophagia) disgusting.
…[Researcher Ben] Hart and his colleagues hypothesize that canine feces-eating is essentially an obsolete trait that modern dogs inherited from their ancestors, grey wolves. They argued that the consumption of feces by wolves was an evolved adaptation that served to eliminate a major source of intestinal parasites near their dens.
…[Researchers Ray and Lorna Coppinger] proposed that wolves that were more temperamentally tolerant of being around humans would have more access to an abundant new food supply. This would give them a leg up on the Darwinian competition for resources and facilitate the spread of genes associated with tameness. This self-domestication strategy was successful. There are now a billion dogs on Earth compared to 300,000 wolves.
There is ample evidence that human feces can make up a substantial proportion of the daily diet of free-ranging dogs. And, from a dog’s point of view, human feces appears to be tasty and surprisingly nutritious. Given its nutritional value and accessibility, it is certainly reasonable to think that in some places, poop-eating was involved in the evolution of dogs.