It's also suggestive that human grandparents are famously concerned with the well-being of their grandchildren. This is, I think, about as near to a cultural constant as there is. Yeah, there's probably some weird culture where grandparents don't get involved, but I can't think of one offhand. Certainly it's true for all the European and Asian cultures with which I'm familiar.

I can't think of another species where grandparents take a special interest in their grandchildren (as opposed to, say, a generic interest in the young of the herd as a whole). Are there any?