More likely it was just a trait in some dogs and those dogs got selected, which is the way most breeds got developed in the past. It might have been very slight at first, but would have strengthened over generations as that trait was repeatedly selected, as Darwin's chesty pigeons got chestier over generations. If you want to call that evolution, OK, but it's not the same thing as saying the dogs developed the trait in response to human attraction to it.
The context was the dogs doing it on purpose to "bamboozle" people who get the "Aw" thing going when they see it. Of course they developed it genetically. in response to human selection of that trait..
I saw a documentary once about people's relationship with dogs. Apparently there's a village in Africa where the people don't even like dogs; they don't feed them, they don't talk to them, they don't give them names, etc. But the dogs still come into the village, clean up scraps, bark when lions threaten the cattle, etc. They do what dogs do without any regard to how they are treated by humans.
All that are in Hell, choose it. -- CS Lewis That's just egregiously stupid. -- ringo