Regeneration of the mammalian brain: a relic of evolution?

Compared to amphibians, fish, and reptiles, mammals have an impaired capacity to regenerate the brain, despite the presence of a neural stem cell pool. Here, we consider the biological significance of a stem cell source in the human brain by exploring evolutionary trade-offs that may guide retention of regenerative capacity in mammals and the risks and benefits of active neurogenesis in adults. We discuss whether reduced regenerative capacity in humans is adaptive or stochastic and examine the role of the injured and diseased brain environment in preventing efficient brain repair. We discuss the therapeutic potential of activating the latent regenerative potential of the human brain to reverse tissue damage or degeneration and whether this approach carries with it an unanticipated risk of cancer.