> Are there any other cells in the body that are not, over time, replaced? Sure. For instance, female ova. The stock is limited. > Might it be possible that s

> Are there any other cells in the body that are not, over time, replaced? Sure. For instance, female ova. The stock is limited. > Might it be possible that some brains have the ability to generate new neurons, while others do not? The former is obviously the case for rodents at least. Could it differ within the species? I can't see why not, in principle. > Couldn't it be possible that evolution created such situations? I imagine it's more about gradual loss of function. For example, in larger brains it's progressively harder (and less probable) to transport the neuroblast to the area where its growth would be beneficial for the brain at large. Thus, eventually adult neurogenesis ceased to increase fitness in large mammals, became effectively an atavism, and mutation load disabled some relevant genes, but it still could hang on a few pathways that either work or do net depending on specific alleles present in the population.