If you read about the various famines in the last 60 years, you'll find that one of the big 
reasons why some underdeveloped  countries  have them so frequently is that they are 
too dependent on one or two 
staples(usually poor foods such as tubers, like cassava etc- cassava contains cyanogenic 
compunds so must be fermented, grated and left out in the sun so that the cyanide can 
evaporate, it also needs to be cooked beforehand, and has been linked to the deficiency-
disease kwashiorkor.) The trouble with tubers is 
that they commonly have antinutrients in them, and are deficient in a number of key  
trace nutrients, so become a problem if consumed in more than trace amounts. The other 
point is that the DHA hypothesis holds that it's the DHA in meat that helps to  increase 
brain-size(tubers don't contain DHA in remotely significant amounts, last I checked).

As far as cooking is concerned, it's already been pointed out that the average hominid 
brain-size heavily expanded in size long before cooking was ever invented, so there's 
clearly no link between cooking and brain-size - for that matter, there wasn't that much  
difference in brain-size between archaic homo sapiens(of around 300,000 years ago) and 
Modern Man, whereas the difference in brain-size between Homo Erectus and modern 
man or between Homo Australopithecus and Home Erectus was pretty large - so if one 
were to take the line that absolutely all current dietary habits re cooking or whatever 
were directly related  
to greater  brain-size , then that would imply that eating raw meat was far more effective 
than eating any cooked-food(meats  or tubers) as regards increasing the average hominid 
brain-size.

At any rate, as www.beyondveg.com pointed out, our Neolithic ancestors greatly 
increased their intake of starchy foods, yet their average brain-size(by comparison to 
their Palaeo ancestors) actually decreased in tandem with this practice(by c. 8%), thus 
appearing to indicate that eating tubers actually decreases brain-size. 

Geoff



Why famine only?  Tubers are a high energy density food. They are not unduly difficult to 
gather. The Expensive Tissue hypothesis, which I accept, stipulates that the evolutionary 
decrease in the gut-brain ratio depends on a higher density diet. I believe meat must 
have dominated but I don't see any reason to suppose it did so to the exclusion of other 
high density foods, such as tubers. Moreover, the fact that cooking shows up about 
25-50,000 years before homo sapiens, but a long time before the Neolithic, is at least 
suggestive. I understand that paleolithic tubers would have been pretty gnarly in 
comparison with modern selectively bred mega-starches but I just don't see any reason to 
think that paleo people ignored them.