Reduced Adult Neurogenesis in Humans Results From a Tradeoff Rather Than Direct Negative Selection

The reduction of adult neurogenesis in the human brain, compared to other vertebrate species, has been proposed to result from an active counter-selection to permit the stability of circuits needed for long-term memorization and higher cognitive abilities. Here, bringing forward behavior studies and evolution-based observations, we discuss the benefits of adult neurogenesis and data suggesting that its loss is unlinked with cognitive levels. Considering cell lineages and functional assays, we further note that human-specific genomic features (such as novel gene variants or regulatory sequences) frequently hit pathways that may lead to the premature exhaustion of embryonic neural progenitors after the developmental phase of cortex formation. We propose that reduced adult neurogenesis in humans may be a tradeoff for these changes, themselves selected for to permit the enlargement and complexification of the cerebral cortex during development.