The fact that the human brain burns about a fifth of humans’ total daily caloric intake is a testament to the evolutionary advantages that our intellectual abilities provide us with: the brain’s contributions must somehow more than pay for that sizable fuel bill. On the other hand, we can also infer that a substantially more complex brain probably didn’t provide sufficient dividends, evolutionarily speaking. We’re as brainy as we have needed to be, but not extravagantly more so.
