Matthew Sweet talks to Antony Gormley about his gigantic new sculpture Model. The leading Sondheim interpreter Maria Friedman reveals why she has decided to move from acting to directing for a new production of Sondheim's Merrily We Roll Along. Matthew is joined by the psychologists Nicholas Humphrey and Thomas Hill to debate whether we are as smart as we used to be. And as the literary archive of the great Russian film-maker Andrei Tarkovsky comes up for auction, Matthew looks at his potent legacy.