Rachel Caspari discusses the evolution of grandparents in this interesting Scientific American article.
Using dental techniques for estimating age based on the degree of tooth wear and dental eruption sequences, Caspari and colleagues calculated a simple ratio of old individuals (>30 years) to young individuals (<30 years). They discovered that the number of old individuals increased slowly from australopithicines onward, but the number skyrocketed upward in modern humans of the Upper Paleolithic. Caspari argues that increased numbers of oldsters, possibly as a result of some cultural shift, started a positive feedback loop which led to increasing cultural complexity in modern humans during the Upper Paleolithic. In other words, learning the complex behaviors characteristic of modern humans becomes possible when you have your wise old granny and grandpa to teach you.
Thanks to Mimi Myrtille for bringing this article to my attention in a Facebook Post.