Why is slow life history correlated with intelligence?

Smart animals tend to mature late.  Why?

First, investing in structures such as brains that will only begin to yield benefits afer a considerable delay makes no sense unless there is a reasonable life expectancy at the time the investment is made.  Second, cognitive abilities are adaptations, which means that they should improve survival and so indirectly select for slower life histories.   Finally, because growing brains are critically sensitive to nutrient shortages, growing a large brain is risky; the production of unfit morons is best avoided by keeping the brain on a very conservative growth trajectory.  That takes lots of time, and only organisms that tend toward slow development in the first place have that kind of time.  For all these reasons, we expect that cognition and life history will evolve in lockstep.  Indeed, there is evidence for such correlated evolution among a wide array of mammals -- and, importantly, among primates as well.

That is from Carel van Schaik's excellent Among Orangutans: Red Apes and the Rise of Human Culture.

Addendum: MR reader Sanjay Krishanswamy is not convinced:

...corvids and psittacines [have cognitive powers superior to most apes].  That's really the culmination of studies beginning in the
1970's (most famously Irene Pepperberg's studies on grey parrots and Herrnstein's on pigeons) and is something that has only just become, I think, mainstream biological thought around now: but it rests on as firm experimental obsrvation as any studies of primates (certainly of orangutans).  Corvids and psittacines simply outperform even chimpanzees in many ways.  ...On the other hand, the selective pressures on birds are pretty nasty. Their biochemistry seems a hell of a lot better than ours (witness the longevity of these things).  So perhaps it's an alternate route to great intelligence: if you know that say four out of five young are going to die anyway you can take the risk of 80% of the offspring being quickly developed morons.  I don't know enough about the field to validate that but I think it's an interesting idea.