Last week, we talked about smart (and naughty) monkeys, and today we look more closely at what 'smart' means. 

Intelligent? According to our astrobiologist guest today, it's a human-centric notion. We sit at the top of the evolutionary tree. Or at least, that's we want to believe.

And what of little green men, with sparkling intelligence?

Then we look at alternative an theory on the origin of cancer. Dr Charley Linweaver and his colleague, Prof Paul Davies bring an outside perspective.

Brought to you by Eleanor and Rod.

Next week: chemistry with Dr Colin Jackson