Over the holidays I read The Body: An Occupant’s Guide by Bill Bryson, one of my favorite authors. It is well-researched, captivating, and enlightening. It loses steam in the third and final act, however, which is why I dock it a single star, while still recommending it. These are my favorite passages:

• It’s a slightly humbling thought that the genes you carry are immensely ancient and possibly—so far anyway—eternal. You will die and fade away, but your genes will go on and on so long as you and your descendants continue to produce offspring. And it is surely astounding to reflect that not once in the three billion years since life began has your personal line of descent been broken. For you to be here now, every one of your ancestors had to successfully pass on its genetic material to a new generation before being snuffed out or otherwise sidetracked from the procreative process. That’s quite a chain of success.
• The body is often likened to a machine, but it is so much more than that. It works twenty-four hours a day for decades without (for the most part) needing regular servicing or the installation of spare parts, runs on water and a few organic compounds, is soft and rather lovely, is accommodatingly mobile and pliant, reproduces itself with enthusiasm, makes jokes, feels affection, appreciates a red sunset and a cooling breeze. How many machines do you know that can do any of that? There is no question about it. You are truly a wonder.
• With such an unrelenting work rate, it is a miracle that most hearts last as long as they do. Every hour your heart dispenses around 70 gallons of blood. That’s 1,680 gallons in a day—more gallons pushed through you in a day than you are likely to put in your car in a year.
• Even with the advantage of clothing, shelter, and boundless ingenuity, humans can manage to live on only about 12 percent of Earth’s land area and just 4 percent of the total surface area if you include the seas. It is a sobering thought that 96 percent of our planet is off-limits to us.
• When a teenager struggles to get up in the morning, that isn’t laziness; it’s biology. Matters are compounded in America by what The New York Times in an editorial called “a dangerous tradition: starting high school abnormally early.” According to the Times, 86 percent of U.S. high schools start their day before 8:30 a.m., and 10 percent start before 7:30. Later start times have been shown to produce better attendance, better test results, fewer car accidents, and even less depression and self-harm.
• Medical science has never produced a more noble and selfless group of investigators than the pathologists and parasitologists who risked and all too often lost their lives in trying to conquer the most pernicious of the world’s diseases in the late nineteenth and early twentieth centuries. There ought to be a monument to them somewhere.
• As Daniel Lieberman told me, reaching 80 is largely a consequence of following a healthy lifestyle, but after that it is almost entirely a matter of genes. Or as Bernard Starr, a professor emeritus at City University of New York, put it, “The best way to assure longevity is to pick your parents.”
• It is an extraordinary fact that having good and loving relationships physically alters your DNA. Conversely, a 2010 U.S. study found, not having such relationships doubles your risk of dying from any cause.