"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.
Increased encephalization has evolutionary costs - high energy expenditure and (in humans) difficult birth of underdeveloped infants due to head size. Natural selection will not allow encephalization beyond a certain size unless it has offsetting benefits, which depend on the species and its environment. So it's not a random walk (=neutral genetic drift) once you get far enough from the average, like we have.