Sequencing - the careful striptease by which you reveal information to the reader - matters in an article, but it is absolutely essential to a book.

Monotony collapses time; novelty unfolds it. You can exercise daily and eat healthily and live a long life, while experiencing a short one. If you spend your life sitting in a cubicle and passing papers, one day is bound to blend unmemorably into the next - and disappear.

I met with amnesiacs and savants, educators and scientists, to try to understand what memory is, why it works, why it sometimes doesn't, and what its potential might be.

If you were a medieval scholar reading a book, you knew that there was a reasonable likelihood you'd never see that particular text again, and so a high premium was placed on remembering what you read. You couldn't just pull a book off the shelf to consult it for a quote or an idea.

There are two possibilities: Either the kiss is a human universal, one of the constellation of innate traits, including language and laughter, that unites us as a species, or it is an invention, like fire or wearing clothes, an idea so good that it was bound to metastasize across the globe.

To the extent that experience is the sum of our memories and wisdom the sum of experience, having a better memory would mean knowing not only more about the world, but also more about myself.