i do believe cooking gave us our big brains.
Kyle Inuit ate cooked meats.
basically you have these hunter gather tribes that were completely cut off from the civilized world for thousands of years, have no outside contact. THese people cook most of there meat, although some do eat a decent amount of raw foods, but most are predominately cooked. Now why do they do this? if raw meat was easier to digest, gave them more energy, produced healthy off spring these people would most certainly be eating an all raw diet, but thats simply not the case. this is a reason im having a hard time into doing an all raw diet.
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Just to clarify, while the Inuit did actually eat large amounts of raw meats including lots of raw "high-meat"(especially the nutrient-denser organ-meats), they did eat some cooked meat as well- BUT it was boiled, so not heavily cooked. It should also be noted that the partially-raw-meat-eating Eskimos have the largest skulls of modern humans:-
http://books.google.co.uk/books?id=mHFsScY8ewMC&pg=PA101&lpg=PA101&dq=inuit+largest+brains&source=web&ots=The above, along with my points debunking the whole theory in the above link provided further up, should make it clear that the whole notion re cooked-food leading to bigger brains is nonsense. As regards the whole issue re brains, though, it should be made clear that the key nutrient providing for larger brains is meat, as opposed to the whole issue of raw vs cooked. Hominids got larger brains as they increased the amounts of meat in their diet, whether raw or cooked, and there's no such correlation between the advent of cooking and brains.
As regards the Inuit hunter-gatherers, it's absurd to suggest that they must have turned to cooked meats because were supposedly easier to digest. For one thing, humans do very stupid things such as smoking, taking drugs, consuming alcohol etc., all of which are harmful, so it's not logical to assume that people will follow the healthiest diet around - a far more likely explanation is that the opioids(present in cooked-foods, as well as dairy/grains) made cooked-food more addictive than raw foods, thus encouraging consumption of the former. Plus, there's the extremely cold Arctic climate, which might force Inuit tribes to cook some of their meats for obvious reasons.
Also, I believe you said you were trying a Wai diet - given all that fruit/carbs I'm not surprised you're not doing well on it. Add some raw animal fats/organs etc., and you'll do much better. After all, it's inconceivable that palaeo humans just ate a little raw fish and lots of raw fruit and raw eggs, and nothing else.