Leprosy goes under the microscope this week as we uncover the origins of one of the oldest known human diseases, recognised this week on World Leprosy Day. A quarter of a million new cases are diagnosed every year, but how is the illness spreading, what damage does it do to the body and can it be stopped? We also hear what archaeologists are unearthing about the history of leprosy and where it came from in the first place. Plus, why it's time to rethink the workings of the circadian clock, brain scans for bilingualism, cow-stomach bacterial genes for biofuels, and the engineering that lies behind the cat's eye...