The expensive tissue hypothesis (ETH), which was first put forward in the 1990s, suggests our selfish brains are prioritised when we have to think fast and work hard at the same time.
Researchers believe that a kilogram of brain tissue needs around 240 kilocalories each day to function at full capacity.
Our ability to allocate more glucose to the brain could have helped our species survive and thrive by becoming quick thinkers, experts believe.
The ETH theory has previously been disputed. For example in 2011 researchers from the University of Zurich questioned the theory animals with big brains really had smaller guts.
Now, researchers led by Magdalena Muchlinkski at the University of North Texas in Fort Worth have explored the theory by looking at ten cadavers of