If the hippocampal–entorhinal cortex system were developed only for navigation, the large combinatorial space and the large numbers of potential cell assembly combinations would be surprising. First, insects can navigate effectively with much simpler circuits and many fewer neurons40. Second, in navigating rats, the local environment can be mapped at centimeter precision by just a dozen or so grid cells33 or place cells41. We suggest that the rich variety of orthogonal representations generated by the modular representation of space during mammalian evolution laid the ground for storing independent representations for the wide variety of environments and experiences encountered by the animal every day. This enlarged representational capacity of environmental details could be what distinguishes the mammalian brain from the brains of species in which navigation is based on much smaller circuits.
