Odd...
Just watched an advert on tv, and it was advertising a magazine for kids about the human body. One of the 'sample' things was “why is my brain wrinkly”.
So, doing a google search on this (who doesn't want to know why their brain is wrinkly?), i came across this site - good for a laugh...
(btw, apparently its because “the cortical folding makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it” [from theanswerbank] See? You even learn stuff on this blog... <IMG alt=":)" class="emoticon" src="/images/emotions/emotion-1.gif" border=0>) .