Robin: Species boundaries are pretty hard boundaries to the transfer of useful genetic information. So once proto-humans stumbled on key brain innovations there really wasn't much of a way to transfer that to chimps. The innovation could only spread via the spread of humans. But within the human world innovations have spread not just by displacement, but also by imitation and communication. Yes conflicting cultures, languages, and other standards often limit the spread of innovations between humans, but even so this info leakage has limited the relative gains to those first with an innovation. The key question is then what barriers to the spread of innovation would prevent this situation from continuing with future innovations.

If there's a way in which I've been shocked by how our disagreement has proceeded so far, it's the extent to which you think that vanilla abstractions of economic growth and productivity improvements suffice to cover the domain of brainware increases in intelligence: Engelbart's mouse as analogous to e.g. a bigger prefrontal cortex. We don't seem to be thinking in the same terms at all.

To me, the answer to the above question seems entirely obvious - the intelligence explosion will run on brainware rewrites and, to a lesser extent, hardware improvements. Even in the (unlikely) event that an economy of trade develops among AIs sharing improved brainware and improved hardware, a human can't step in and use off-the-shelf an improved cortical algorithm or neurons that run at higher speeds. Not without technology so advanced that the AI could build a much better brain from scratch using the same resource expenditure.

The genetic barrier between chimps and humans is now permeable in the sense that humans could deliberately transfer genes horizontally, but it took rather a large tech advantage to get to that point...