Brain evolution: Was it all cooking?

I have seen this new article about how metabolism affected brain evolution emerge in several places this week (1).  I think it is, for the most part, a great article, and would recommend it to any one with interest in this area.  Anything with math usually gets my attention, and this article uses math to support its hypothesis in an easy to understand way.  However, I am not sure that I can fully support the conclusions the authors, and many others, have come to about how their data relates to cooking.

If we take a closer look at the article we can see that the main point being made is that there is simply not enough time in a day to take in enough energy to support both a large body and a large brain.  They make the point that the human brain accounts for only 2% of body weight, but consumes 20% of our energy.  Another interesting fact they have is that for every billion neurons we have we need to consume about 6kcal to fuel them.  Using this data they hypothesize that if we were to eat the same diet as our great ape relatives, we would have to spend over 9 hours every day eating to get enough energy to support our brains and body.  Do any of you spend  9 hours eating?  I didn't think so.

This eating constraint is the real result of the paper, and not the ways we overcame it.  It is in the discussion they discuss reasons why we, as early humans, were able to overcome the constraint and develop our large brains.  To quote the authors:

"such a metabolic limitation was overcome in the human lineage by the advent of cooking food, which greatly increases the caloric yield of the diet, as a result of the greater ease of chewing, digestion, and absorption of foods"

However, I think a lot of other adaptations were taking place in early humans that allowed us to develop our brains. I have written before about how important fat is a brain fuel, and when we switched from the herbivorous diet of our great ape relatives into one that included more animal products we also started consuming more fat.  Let's review our basic nutrition facts quick: Carbohydrate=4 kcal/g Fat=9 kcal/g.  For every one hour we spend eating fat we gain over twice the amount of energy.

I think our reliance on fat as a primary source of energy was probably more important than our adoption of cooking.  This doesn't mean we can throw out cooking, I do believe that cooking played an important role in making us distinctly human.  I just don't think that it was the sole, or even largest, factor in our transformation like these authors seem too.  Again, I think I think this is a great article, I just wanted to provide some food for thought for those of you who have read this article or have seen it popping up around the web!