"The Planet-of-the-Apes Hypothesis" Revisited --Will Intelligence be a Constant in the Universe?
If intelligence is good for every environment, we would see a trend in the encephalization quotient among all organisms as a function of time. The data does not show that. The evidence on Earth points to exactly the opposite conclusion. Earth had independent experiments in evolution thanks to continental drift. New Zealand, Madagascar, India, South America... half a dozen experiments over 10, 20, 50, even 100 million years of independent evolution did not produce anything that was more human-like than when it started. So it's a silly idea to think that species will evolve toward us.
A random walk away from no brain by a large number of lineages would also give you a constantly increasing upper bound on brain size.
That was S. J. Gould's model - in Life's Grandeur. Assuming that a trait like brain size behaves as though it is a neutral trait seems pretty loopy, though. Now we have enormous data centres to explain, the "random drift" model is surely no longer worth entertaining.