It has been mentioned on beyondveg.com and elsewhere that average human brain-size decreased by c. 8% in the last 10,000 years following consumption of large amounts of starch. The following article mentions how pregnant women ingesting lots of acrylamide, a type of toxin created by cooking foods(especially starches) eventually gave birth to babies with smaller infant brain-sizes:-

http://www.telegraph.co.uk/health/healthnews/9627375/Chips-in-pregnancy-can-cause-underweight-babies.html

Geoff