According to this story at Softpedia, genetic researchers at the University of Lausanne in Switzerland have determined that "there is a definite correlation between the mental capabilities of a fly and its life longevity."
As it turns out, the dumber they are, the longer they live.
- Why this is happening is not quite known, albeit the researchers speculated that the most likely cause is the increase in neural activity of the flies, which triggers an imbalance in the life-support system, leading to a much shorter lifespan than they would have had if they had been left in their natural state.
"This would explain why flies, like most other animals, have hardly developed their neural capacities", the researchers said.
— Larry, Attack Monkey, Light Reading