Let's consider an interesting fact: Over the past 10,000 years, on average the human brain in both males and females has shrunk in size by about 100 cubic centimeters - roughly 7 percent. (And, for what it's worth, our skulls have gotten thinner.) Should we be worried about this, given that expanding brain size is one of the major measures by which scientists have traced the rise of modern humans over their hominid and their still later ancestors, all of whom have gone extinct?
(Of course I'm tempted to talk politics now, but let's not go there.)
The question is why our brains are shrinking. The fact is that nobody knows why, or what it might mean for the future. One suggested reason for the decrease has to do with famines over that time period, as populations grew large and precarious, and crops - invented with farming 10,000 years ago - failed. It makes evolutionary sense that in times of famine, energy-hungry organs such as the brain would get smaller if food shortages persisted. Another idea about why brains are getting smaller has to do with the fact that as humans moved into cities they no longer had to learn all the details of their widespread hunting grounds. But one would think that such changes would be offset by the need for increased social interaction.
I would suggest that this brain-size thing is just one of the twists and turns of evolution that we simply don't understand, and not to worry. Maybe we're just getting more efficient, brain-wise. I will, however, to do my part, keep working those Sudoku puzzles.