* Birthing prematurely compared to other species (most species live young are functional at birth) in order to fit the brain through the hips. * Permanently reducing the mothers top speed (wider hips means the joints are exposed to higher forces while walking). * Requiring 5% or so more food.
All three of those have been serious impediments to human survival for most of our existence, and provided a counter-pressure against improvements in biological intelligence.
In the past century, the Haber-Bosch process has meant we can reliably grow enough food without pursuit hunting. Without that counterpressure, evolutionary improvement seems very likely, but will take hundreds of thousands of years without genetic engineering or eugenics (neither of which seems like a good idea to me).