Some stem cell populations, like those in the brain, decrease significantly after puberty, while others persist throughout life.

“At that point, many of the stem cell populations disappear. For instance, past puberty, and probably earlier, you don't get many more new brain cells. You get a few, but you don't get many more new brain cells because the brain doesn't have many stem cell populations, whereas other organs in your body maintain little pockets of stem cells, or in some cases, many stem cells that can give rise to more and more of that tissue across the lifespan.”