"how much of that do you figure is just anthropomorphizing"? I wouldn't say this is a matter of anthropomorphizing at all, especially now that I've seen the video of lion/antelope, as obviously animals or mammals at least, behave in this way and its not just a characteristic of humans.
It would have been interesting to see if these adoptive mothers would have aggressively protected their 'babies' from predators in the same manner as protecting their own