June 4 (Bloomberg) -- Fruit flies that are more mentally developed die at an earlier age than their more ignorant counterparts, a study by scientists at the University of Lausanne in Switzerland showed.

Researchers Joep Burger and Tadeusz Kawecki managed to boost the mental capacity of a group of flies by teaching them how to associate a smell with a taste, such as with a sweet or sour drink, or an unpleasant experience like the rattling of a box they were in. Over 30 to 40 generations, the insects developed better memory or the ability to avoid the rattling box, the researchers found.

``Still, we rapidly discovered that these flies lived shorter lives,'' Burger said today in a telephone interview. The other group, left in a natural state, lived 80-85 days on average compared with 50-60 days for the more intelligent ones, he said.

One cause may be that flies with an active brain burn more energy than the others, according to the researchers. This high cost -- earlier death -- would explain why flies, like most animals, have hardly developed their neural capacities.

``We're still speculating on the reasons at this stage but there seems to be a certain cost of learning,'' Burger said.

The Dutch scientist refused to draw conclusions for human beings, saying proper studies aren't available.

``We chose flies because they can reproduce themselves within 14 days,'' the scientist said. ``I would take hundreds of years to do this with human beings, without mentioning the fact you can't perform selection on them.''

The study results have been published in the International Journal of Organic Evolution. The university released the results today from studies that Burger started working on in 2006.

To contact the reporter on this story: Marc Wolfensberger in Bern at mwolfens@bloomberg.net

Last Updated: June 4, 2008 10:56 EDT