ABSTRACT
We look back in time to an implausible scenario in the age of hunter-gatherers to gain an appreciation of the importance of brain energy ef€ciency for the evolution of our species. Imagine getting up in the morning, eating breakfast, brushing your teeth, taking the kids to arrow-making school, and then starting your day’s routine of searching for enough food to feed your family. From 9:00 a.m. to noon you roam and search for enough food to satisfy the energy needs of your own brain. It is well after dark before you return home with food for the rest of your family. Because 20 to 25 percent of our ancestor’s waking time is a minimum required for the gathering of brain food, it is easy to de€ne brain ef€ciency in terms of the hours spent each day on feeding the voracious energy appetite of this 3-pound organ alone. If the brain were miraculously made more energy ef€cient; say by 33 percent, our ancestors could have knocked off looking for their own brain food at 11:00 a.m. rather than noon (i.e., more leisure time) and could have returned home before dark in time to avoid saber-toothed tigers that hunted at dusk. But this brain miracle never happened; instead brain ef€ciency is believed to have maxed out by the era of huntergatherers. Obviously, as we enter the age of obesity, €nding enough food for our brain is not a high priority; but keep in mind that there are still parts of the world where it does matter.
