No argument that the modern "pet" relationship is a byproduct of domestication. Except for cats, that is -- I suspect that symbiosis is entirely under the control of the feline partner.

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I haven't researched yet, so I'm just blue-skying about pre-history: Conclusive evidence of canine domestication will be difficult to find without a deliberate burial. Canine bones found in a midden probably can't be differentiated from "casual food source". Otherwise, a death in a communal pack would be left exposed, especially while traveling.

The basic scene is easy to play out: dogs and humans are both pack animals, and both can be scavengers. Four-legs learns to follow two-legs, for the leftovers. On the other paw, the key to the emotional link is with the young of both species, puppies and children, and mammalian play. The story of Mowgli is fiction, but its mirror did happen, the very first wolf cub raised by the Man-pack... as did the very first child to say "He followed me home, Ma -- can I keep him?"

I have a bit of trouble with finding the origins of human/canine cooperation much before archaic H. sap. (stone tools, after all, go back to H. habilis). For one thing, earlier hominids were markedly smaller, more prone to be prey than master . In any case, "safety in numbers" behaviors shared across the whole primate family protects groups and preserves their collective genome without reliance on other species. Predators take individuals.

Another point I just thought of, which still holds true: A certain threshold of resources is needed to support mixed-species communality, just as it is to support growth of a single-species pack. More mouths to feed. The deeper into the past you go, the leaner the pickings. You can't bribe and reward a carnivore for cooperation with a diet of insects and roots. "Nuts and berries, yuk!"

My guess is, canine domestication is intertwined with the transition from foraging to the hunting of megafauna. (Are dogs depicted in Lascaux or Altimira? I don't know, at the moment... more research!) Unfortunately, herd-following nomads leave very little evidence, since their artifacts are nearly all biodegradable.