http://www.m.webmd.com/a-to-z-guides/news/20151016/big-brain-doesnt-mean-big-smarts?src=RSS_PUBLIC
From their website;
Having a big brain doesn’t guarantee you’ll have an outsized IQ, a new analysis indicates.
Researchers who examined 148 studies that included more than 8,000 people found only a weak association between brain size and IQ.