Humanity might be able to, humans cannot

Not smarter in terms of reasoning ability. Just able to draw on the collective experience from all those who lived prior.

Evolution and human intelligence are two entirely separate optimizers. Evolution improving intellence is not an example of self-improvement, recursive or not. Evolution improving evolution itself would be a self-improvement process. Human intelligence improving human intelligence would be a self-improvement process. Both processes do exist in a weak sense, and future technological advances might allow human self-improvement to a much higher degree. Indeed human intelligence augmentation has always been considered one of the potential (if not the most plausible) ways to superintelligence.

This is all rather rudimentary stuff discussed in detail in the so-called "Sequences", the long series of Less Wrong posts by Yudkowsky back around 2010.