In the beginning, there was insulin.

It was a billion years ago, before the Flintstones split off from jellyfish, that nature first found the crucial hormone that regulates life-span and metabolism from worms to man.

But insulin, for all its virtues, also helps keep life spans short, a recent study shows.

Scientists have known for a while that roundworms insensitive to insulin live up to three times their species' average life span of 10 days.

This month, Harvard researchers reported that it is in the brain of the roundworm that insulin-like signaling controls life span.

The findings, published by Professor of Genetics Gary Ruvkun in the Oct. 6 issue of the journal Science, suggest that the brain may have a bigger role in controlling aging than was previously thought.

Roundworms that have longer than normal life spans have been kicking around in genetics laboratories for more than 20 years, first made by severely inbreeding families of worms and by exposing worms to harmful chemicals that cause mutations.

But only in recent years did researchers, using powerful new tools of molecular biology, learn that it is a defect in these worms' insulin systems that causes their long life.