Book review: The Great Divide

The Great Divide: Nature and Human Nature in the Old World and the New by Peter Watson (2013-06-25)

I was quite eager to read this book. It’s about the roughly 16,000 years in which the world contained two entirely separate populations of humans, one in the Old World and one in the New; the author describes this time period as a huge natural experiment. Although these two groups were obviously very similar, this book focuses on the ways that differences arose between them as they responded to their natural environments and experiences. 

I love big-picture, big-history books like this that integrate information from a range of disciplines, and I’ve wondered in particular about how religious beliefs are shaped by the physical environment, which seems to be an important part of this book. In the beginning, I found the book fascinating and even exciting, but I quit reading after about 100 pages.

The trouble really started when I got to a bit about how variations in Earth’s orbit and rotation affect climate. I was bothered by the way the author described a particular orbital/climate cycle.1 You expect a certain amount of hand-waving and speculation in a book that spans so many areas of study and such a vast time frame, but this seemed to be a failure to grasp the material well enough to explain it clearly. That bothers me in a book that covers so many areas where I’m ignorant and hoping to learn. If I’m tripping over things in a subject I know something about, am I missing similar misunderstandings or errors on topics where I lack the expertise to evaluate the information?

Sometimes you can overlook flaws in a book like this because it serves as a good-enough introduction to unfamiliar areas, with pointers to where to learn more. I appreciated that Watson named many of the scientists whose work he described in the chapters I read, and he cited some scientific papers as well as books. However, I unfortunately discovered what I considered to be gaps in his supporting information.

One useful thing an author can do is give readers the name of an event or hypothesis or phenomenon so that they have a handy search phrase. I went to Google for more information about one of the most exciting things I read about in the book, a hypothesized cometary impact about 12,900 years ago that might have had something to do with the extinction of North America’s megafauna. I Googled something like “comet 12900 bp” and learned that the idea is referred to as the Younger Dryas impact hypothesis.2

What a name! Why hadn’t the author used it in his book, as a handy hook for readers who want to know more about this mysterious comet? Maybe he did and I forgot. But no, he doesn’t even name any of the authors on the paper he mentions. Worse, the footnote numbers in the chapter appear to be off by one, so the footnote to the sentence describing that paper refers to something else entirely, and the proper citation is in the next footnote.

It’s a small thing, and maybe it was just bad luck that the first footnote I checked was messed up. Still, in my work as an editor, I’ve spent a fair amount of time doing frustrating battle with incomplete, inaccurate, or incorrectly numbered citations so that readers won’t have to, and I’m irritated by the lack of courtesy implicit in sloppy citations. (To be fair to the author, I think HarperCollins probably could have exerted some effort to clean up various infelicities, and perhaps some of them have been fixed in the paperback.)

The beginning of the end for me came when the book went back to talking about the Earth’s orbit: “We have already seen how the orbits of the Earth in relation to the sun determines Ice Ages and interglacials … .” Leaving aside the “orbits … determines” gaffe, I wondered: Orbits? Does he mean “orbital and rotational motions“? Probably, but why say “in relation to the sun”? What else would we be orbiting in relation to?

I can only guess at the difficulties of synthesizing a huge amount of information across a broad range of fields, and I have to respect a writer for trying. Still, maybe hiring a research assistant would have been a good idea, or asking experts in various fields to review certain parts. I really get the feeling this author doesn’t understand some of what he’s talking about. And that means it’s hard to trust him.

I didn’t want to give up on this book. It had promised so much. I thought maybe it was worth sticking with because other areas are handled with greater mastery. I Googled around and found, among other things, a review in the Guardian by Tom Holland, who is knowledgeable about the ancient world. Despite his overall positive take, the reservations he mentioned about information in his field helped persuade me to walk away from the book.3

I’ve encountered a feeling among some academics that popularizers are something of a lesser breed. If they were real scholars (in particular, real scientists), they’d be publishing in scientific journals, not writing books. As a reader who relishes the big picture, I greatly appreciate popularizers who do their job well. However, books like Watson’s almost persuade me that maybe the experts are right when they complain about people who present their material sloppily, or oversimplify it, or don’t fully grasp the details. And that makes me sad, because well-written books that give nonspecialists a trustworthy cross-disciplinary introduction to interesting research can provide a valuable bridge between the scholarly literature and the average reader. Overall this book struck me as a missed opportunity.


1 The book describes a 100,000-year cycle as arising “from the Earth’s orbit around the sun, which is elliptical and means that the distance from Earth to sun varies by as much as 18.26 million miles, producing marked variations in the force of gravity” (p. 30 in the hardback). This doesn’t really explain how the cycle works (not to mention being a rather sloppily written sentence), and the important part about this cycle has nothing to do with the force of gravity. What’s going on is that the Earth’s orbit slowly changes from more circular to more elliptical, and then back again. When it’s at its most elliptical, the difference in Earth’s distance from the sun at different times of year, and thus the difference in how much energy from the sun we receive at different times of year, is much greater. The 18.26 million mile variation that he mentions would mean a lot more, I think, if he noted that the current variation is about 3.1 million miles (we’re about 3.1 million miles closer to the sun in January than in July). NASA has a nice page explaining how recurring changes in Earth’s orbit and rotation affect climate.

2 It appears to be a troubled hypothesis, unfortunately. Drat. I was so thrilled by the idea of nanodiamonds and helium-3 at Clovis sites.

3 On the plus side, I discovered Tom Holland, who wrote some books that look interesting.