Adult neurogenesis? Not so much in humans

This is a huge result, making NPR and published in Nature, here. Since the discovery of adult neurogenesis in rodent models, it has been assumed by many (but not all) that we humans did the same thing. The assumption was that we grow new neurons every day throughout our lives.

Aside: actually that assumption was contrary to what many of us were taught. Before the discovery of rodent adult neurogenesis, it was thought humans stopped producing new nerve cells with the onset of adulthood.

The latest findings indicate that in humans, the production of new neurons slows down by age 7 and is gone by age 13. That’s shocking. What was the selection pressure for loosing such a phenotype from rats and mice?