`Why life?' Questions of this type were for a long time the prerogative of philosophers who left the `how' question to scientists. Nowadays, Darwin's successors no longer have any qualms about addressing the `why' as well as the `how'. Over a century ago, Darwin modestly admitted having 'thrown some light on the origin of species - this mystery of mysteries'. Two major advances in the following decades helped biologists answer many of the questions he left unsolved. The first was the discov ...