New neurons for 'survival of the fittest'.

Adult neurogenesis is often considered an archaic trait that has undergone a 'phylogenetic reduction' from amphibian ancestors to humans. However, adult neurogenesis in the hippocampal dentate gyrus might actually be a late-evolved trait. In non-mammals, adult hippocampal neurogenesis is not restricted to the equivalents of the dentate gyrus, which also show different connectivity and functionality compared to their mammalian counterpart. Moving actively in a changing world and dealing with novelty and complexity regulate adult neurogenesis. New neurons might thus provide the cognitive adaptability to conquer ecological niches rich with challenging stimuli.