Light lifting. This was like a Malcolm Gladwell book on sleep - but not as well written. Not to say it was bad - I certainly enjoyed it - but this was more like 10 sequential magazine articles than it was a book. It just barely skims the surface of many topics, hits the talking points, and moves on. I'd really like something a lot deeper, but can't complain too much about this offering. I don't think there was anything here I hadn't seen before - but worth calling out:

• No one really knows why we need sleep, but it seems to be particularly related to relaxing the prefrontal cortex.
• Discussed the idea (which came up in How The Mind Works) about the purpose of dreams being to prepare our brains for bad/novel scenarios. Dreams are essentially 'practice' mode for our brains, so that when we experience novel situations in life we'll be better prepared.
• There seems to be evidence that without artificial light, it seems like humans naturally sleep twice a day: 1st sleep, then an hour or so awake, and then 2nd sleep. There's evidence that most people actually did this regularly until just a few hundred years ago.
• Teenagers circadian rhythms make them want to sleep from 12-8, whereas older folks (50+) tend to want to sleep from 9-4. Theory is this was evolutionarily advantageous so that families/groups of humans would always have someone "on shift" looking out for danger. I love this. What an elegant solution to a legitimate, if totally obsolete, problem.