Directionality in evolution without intelligent guidance

[JuliaL]

1 & 2) Starting from no brains, it isn't surprising that the slope of the brain size vs time function is positive. As the width of the distribution of brain sizes increases, you pretty much have to have some big brains in the upper tail. There are enough examples (parasites who have given up not only their neural complexity, but their digestive systems) to show that brains don't only increase in size and complexity.
3) Again the increase in complex interactions could just be the spread of individuals to fill niches within a limited solution space.

Evolution solves problems of survival and reproduction using the tools it has at hand and only to the degree required. It isn't goal directed to, for instance, make bigger brains for their own sakes. Even if bigger brains are a competitive advantage, they may be restrained by other factors like pelvis size in live bearing mammals.

But with respect to culture:
We are special.
Our big brains have moved the information transfer between individuals and generations in a whole new way. No longer is it only via chemical sequences in DNA/RNA or behaviors like spoken language. Now we have writing. We started with clay tablets and now have tech stable over centuries like xerography or graving on laquer disks (audio).
Oral or behavioral (e.g. teaching your friends to clean yams by washing away the dirt link) transmission is limited to direct contact between individuals. Writing transfers information laterally and longitudinally.
It remains to be seen if the increased speed of evolutionary changes we've added to culture will be its undoing. The rocket is flying, but is showing signs that it might explode at any time.