A major evolutionary innovation has unfurled right in front of researchers'''' eyes. It''''s the first time evolution has been caught in the act of making such a rare and complex new trait.

And because the species in question is a bacterium, scientists have been able to replay history to show how this evolutionary novelty grew from the ac*****ulation of unpredictable, chance events.

Twenty years ago, evolutionary biologist Richard Lenski of Michigan State University in East Lansing, US, took a single Escherichia coli bacterium and used its descendants to found 12 laboratory populations.

The 12 have been growing ever since, gradually ac*****ulating mutations and evolving for more than 44,000 generations, while Lenski watches what happens.

Profound change