Since 2002, the Radiolab hosts Jad Abumrad and Robert Krulwich have been unpacking the mysteries of the cosmos one episode at a time. This season took them from the depths of the ocean to early America, to outer space, and into the human brain for “G,” a multipart series on intelligence that culminates in the hilarious talent contest of “The World’s Smartest Animal.” These six installments are Radiolab at its apex—this crew excels when studying the enigmatic places where science seems to morph into magic, making the mind ideal ground for the team to explore. The show strips away much of the artifice of audio storytelling, avoiding any lectures or self-conscious monologues from the hosts. Given all the stones this series has turned over, it’s a surprise the producers and hosts have anything left to explore—maybe next year they’ll reveal the secrets of their own creativity.