Intelligence is Expensive

A recent study at the Universite Laval in Quebec found that students consume 203 to 253 more calories after 45 minutes of activity requiring intense thought than students who relaxed for the same 45 minutes. Although the brain accounts for less than 2% of a person’s weight, it consumes 20% of the body’s energy. That’s 480 calories of a 2400 calorie diet, and if that energy supply is cut off for just four minutes, permanent brain damage can occur. There is no other organ nearly as sensitive to changes in its energy supply.

Intense physical exercise improves cognition in a variety of ways including staving off mental deterioration in seniors. This may be the result of increased oxygen flow to the brain and the recently discovered phenomena of the brain consuming lactate in addition to glucose during periods of intense exercise.

Homo floresiensis Credit: Kirk E. Smith

Comparisons with human brains found that a race of hobbit-like humans, Homo floresiensis, living in Indonesia 18,000 years ago had smaller brains in addition to their smaller size. Homo floresiensis lived on the island with pygmy elephants, and the two species probably shrank in size due to a scarcity of resources. When times got tough, this branch of humans quickly evolved smaller bodies and smaller brains to feed.

Colony of Tiny Sea Squirts Credit Nick Hobgood

Sea Squirts start life resembling a tadpole. It swims around until it find a suitable rock to affix itself, and then digests its cerebral ganglion, which controlled its movement. In other words, the sea squirt eats its brain when it doesn’t need it anymore. The Evolutionary Philosopher Daniel Dennet observed that this behavior resembles Professors having received tenure.

We tend to take it for granted that intelligence would naturally evolve from life, but the expense in energy does not always justify the gains in survival fitness. All the behavioral malleability that comes with the intelligence our hungry brains provide could conceivably be outwitted by some dumb but elaborate algorithm in another species, such as a virus or bacteria. We have to keep feeding our heads energy and ideas to prevent their being undone.