Although it’s about the dog Buck, it’s actually about Jack London’s philosophy of life, or at least that small part of it we see here. I mean, who’s ever heard of a man reading a dog’s mind?
It’s also important to disentangle the notion of primitive law because it can easily be confused with the notion of "primitive" as in primitive societies. I mean, after all the immense anthropological work done over the course of the 20th century, it turns out that primitive societies are not much different from the societies of the advanced industrial nations. Not a surprising conclusion as they are all sprung from the same root (the difference lies in the technology but not in the society). So again primitive law is something we should understand in terms of Jack London’s philosophy of life and not in terms of law that actually existed in so-called primitive societies.
Jack London here is eliding the notion of primitive law with violence and cunning. Put simply and crudely: it was Buck’s ‘introduction’ to the violence and the cunning of the white man and he met that violence ‘half-way’ by fighting back with violence and cunning. It’s also worth noting that it’s a short fragment that partly misrepresents the fuller significance of Jack London’s philosophy - after all he was a socialist and according to the Sonama News, the Call of the Wild is about:
finding yourself and finding your tribe, and your mates.
But more, to fully understand the meaning of even a part of a novel means that one ought to understand it in the context of both a writer’s oeuvre and times. For example, Sonama News go on to say:
[Jack London is] usually listed as an author intent upon exposing the deterministic world of uncaring Darwinian struggle for survival ... But London’s Naturalism does not only offer bleak despair in the face of what he called Nature on the Yukon: the ‘white silence’; instead as a socialist he offers a hope that humanity - if united in comradeship and brotherhood - and rise above or at least survive the cold dictates of giant Pacific storms, horrors such as the Chilkoot trail ... In the end, although he was passionately naturalistic in outlook, he was passionately idealistic in his hopes for his fellow man and woman.