What does it mean to be a human, or more specifically a humanist? Is it about culture, morals, principles, science, freethinking, feelings or optimism? Or is it all of the above? The author of the new book "Humanly Possible: Seven Hundred Years of Humanist Freethinking, Inquiry, and Hope", says it is all of those things and more. Sarah Bakewell spoke to us in Perspective.