Monkeyluv: And Other Essays on Our Lives as Animals, by Robert M. Sapolsky was a fantastic, educational, funny, well-written book. I absolutely loved it. When it isn't brand-new and it comes down in price, I will buy my own copy to keep (this one was from the library).
Sapolsky is a neurobiologist at Stanford who studies stress hormones and their effect on health. He does field work with baboons in east Africa (detailed more in A Primate's Memoir, which I blogged about here).
In this collection of essays, originally written for magazines like Natural History, Discover, and Men's Health, he writes about our genes and how they interact with our environment. He explains things like why people who think nature always trumps nuture are wrong (or don't know how genes work), depression and PTSD and how a susceptibility for these disorders can be inherited (but not always developed), sexual attraction, dreams, cross-cultural religious patterns, Munchausen's by proxy, and more.
Since the essays were originally written for popular magazines, they are short and very readable. At the end of every essay, he's added a nice "further reading" section that tells you about the research about this issue, more technical works you may want to read, and interesting asides.
This is the kind of popular science we need to see a LOT more. It doesn't oversimplify the issues, but it doesn't bore the reader.
I could go on and gush about every single essay, but I'll stop here and just tell you to read the book if you're at all interested in your biology and your environment and health. Or recent scientific studies on any of these issues.