The female coyote nurses the pups after they are born, yet they are hard to feed and the mother is not in ideal condition for hunting. She therefore regurgitates her food regularly for the pups, and furthermore the biological father brings food too. And yet:
Dogs have evolved a different parental strategy. Human waste tends to show up at the same place daily and so the dogs, as we have noted, have very low transportation and acquisition costs.
The pregnant female village dog can stay by her food source all through pregnancy and lactation. She can locate her den in the middle of the food source. frequently, she goes to some quiet place outside the village (but not too far outside). There are many quiet places in the Mexico City dump. All over the dump are fat nursing pups.
Regurgitation is occasional rather than regular, and the father is absent altogether. In evolutionary terms, it seems that is the result of cooperation with humans.
That is all from the new and excellent book What is a Dog?, by Raymond Coppinger and Lorna Coppinger. The best parts of this book draw inferences from what is observed in Mexican town dumps.