In the model, larger stores of adaptive knowledge favor brains able to hold more and social-learning routes able to transmit more; group size and juvenile period co-evolve with them. The engineering inference is to design capacity and transmission in concert, because either can become the other’s constraint. That feedback sits near the center of Cultural Intelligence: collective capability depends on a coupled social and cognitive substrate.
An evolutionary agent-based model in which brain size, group size, social learning ability, mating structure and the length of the juvenile period all evolve at once rather than being assumed.
Brains grow when there is more adaptive knowledge worth storing and a better route to getting it from others. Group size and juvenile period grow with them, because both raise how much can be learned from someone else.
The runaway human trajectory falls out as a special case, under conditions the model makes explicit. Reading it as an engineering claim: capacity and transmission co-evolve, and building either one alone stalls.