Animals with largest brain volume, not volume relative to body size, have superior cognitive powers, shows a large-scale investigation into the evolution of self-control in animals.
"The study levels the playing field on the question of animal intelligence," said psychologist Lucia Jacobs from University of California Berkeley.
The findings challenge prevailing assumptions that "relative" brain size is a more accurate predictor of intelligence than "absolute" brain size.
The study that relied on data from three-dozen species also found that animals with the most varied diets showed the most self-restraint.
"As brains get larger, the total number of neurons increases and brains tend to become more modularised, perhaps facilitating the evolution of new cognitive networks," said the study.
In one experiment, creatures large and small were tested to see if they would advance toward a clear cylinder visibly containing food - showing a lack of self-restraint - after they had been trained to access the food through a side opening in an opaque cylinder.
Large-brained primates such as gorillas quickly navigated their way to the treat or "bait".
Smaller-brained animals did so with mixed results, said the study.
The study appeared in the journal of the Proceedings of the National Academy of Sciences.
