That's conceivable, and might also explain why wolves, crows, elephants, and other highly social animals aren't as smart as people.

Also, I think the original bit in Methods of Rationality overestimates how easy it is for new ideas to spread. As came up recently here, even if tacit knowledge can be explained, it usually isn't.

This means that if you figure out a better way to chip flint, you might not be able to explain it in words, and even if you can, you might chose to keep it as a family or tribal secret. Inventions could give their inventors an advantage for quite a long time.