My guess is that the mechanism used in our case was similar to that which produces imprinting in ducks and geese. Pinker, a sensible evolutionary psychologist, thinks it is probably because those ancestral parents who were not somehow motivated to nurture their offspring were unlikely to have grandchildren and thus to become ancestors. I was never clear about what Rose thinks. For some seals and sea birds that operate giant collective nurseries, where the young may wander off from their mothers, it appears that both mothers and offspring have evolved olfactory methods of identifying one another. The selection pressure favoring the more discriminating mothers was not great enough to produce a species change.
Natural selection is parsimonious.
It continues just long enough to fashion the ROM or module required to accomplish the necessary result in the environment of evolutionary adaptation. A recent news report tells of a lost dog that had been fitted with a radio collar and was finally located in the den of a mother bear. Each time the dog started to emerge in response to his master's call, the bear gently drew him back again to his new home. My wife and I, like millions of others of our species, are more like the bears than we are like seals in this respect. In most jurisdictions, a person who kills a neighbor's dog or cat is treated by the law like someone who destroyed the neighbor's lawn mower.