Economic historian Gregory Clark created a stir with a new book Farewell to Alms: A Brief Economic History of the World, which argues that culture, biology and "survival of the richest" — rather than coal, political institutions or geography — led to the Industrial Revolution in England and explains why some parts of the world today are so wealthy and others so poor. Clark's book, based on 20 years of quantitative research of historical data — including his examination of the wills of more than 3,000 people in 17th-century England — has provoked strong reactions and has been misunderstood as social Darwinism or a call for an end to foreign aid, neither of which he supports.

The book makes the case that living conditions of humans in pre-industrial societies, like those of other animal populations, were determined by the balance of births and deaths, a principle first described by Thomas Robert Malthus in 1798 in "An Essay on the Principle of Population." The English became richer than the rest of the world, Clark writes, largely due to poor hygiene; the death rate was high and fertility low because pre-industrial Europeans lived in close proximity to human and animal waste and they rarely bathed. However, in England, the wealthy survived in greater numbers and had more children, who moved down the social ladder as their family estates got divided into smaller portions. With that downward mobility,

middle-class values spread throughout the society, a cultural shift that set the stage for a historical event like no other — the Industrial Revolution.

Why should it matter to people today what caused the Industrial Revolution?

In economic history, the Industrial Revolution is the great problem, like the origin of the universe in astronomy or the unification of forces in physics. The thing most people don't understand about the Industrial Revolution is that it's very mysterious. It's a startling development in world history. In the pre-industrial world there weren't many differences between the rich and the poor societies. One of the things that the book shows is that people in England in the 1800s, who lived then in one of the richest societies of the world, were no better off than hunter-gatherers. Why is it we were all poor at one time, but now some societies have become very rich and some places are even poorer? If we can understand the Industrial Revolution, then we have a much better chance of understanding the modern world.

Central to your book is a biological idea, Malthus' model for population growth. How did you come to that?

Quite long ago, I thought, if you have the Malthusian model, you would have these selective pressures within pre-industrial societies, and it would gradually change people's economic behavior. But I had completely given up on pursuing that idea for something like 10 years. Then I saw a paper by some theorists arguing the same thing, and I realized that I could test this idea: I can get data and can see if there is any possibility. The bizarre thing was I thought I would prove the opposite, that the people who stayed on the farm, who were the least adventurous, the least innovative, would be the ones who actually survived to form modern populations. But when I got the data and looked at it, I was astonished to see a very clear pattern, that the rich were taking over the pre-industrial Western world. And even then, it took me a while to realize, oh, I could actually link that up with other changes that were occurring, such as that levels of violence had steadily dropped in English society since 1200, interest rates were going down — and interest rates measure how impatient we are.

Another thing that sparked my interest was Jared Diamond's book (Guns, Germs and Steel: The Fates of Human Societies). In the introduction, he asks, Why are people in New Guinea so much poorer now than Europeans? It's not because Europeans are any smarter than people in New Guinea. In fact, Diamond believes that people in New Guinea are selected by their social structure to be smarter than Europeans. He writes that it's because in New Guinea you live by your wits, while in densely settled pre-industrial Europe disease resistance determines survival.

You take on a lot of presuppositions about our past and turn them upside down. Did that make you nervous?

There was kind of an "aha" moment, when my academic editor said, "People are not going to believe this. The book will be discredited." I said, "I can make a case, and I'm going to take a risk of being wrong." In fact, that's what we should do, that's what everybody should do in writing books. It produces more interesting books. But I wasn't quite prepared for the ferocity of people's reactions. You realize there's a raw nerve out there about potential connections between genetics, economics and race, and it's very tricky getting anywhere near this area. The book is not saying that we got any better through these kinds of pre-industrial mechanisms (or that) we are smarter than people in hunter-gatherer societies. We just have abilities in certain areas that are necessary for a productive capitalist economy.

Kathleen Holder is the associate editor of UC Davis Magazine. She wrote this article for the spring 2008 issue.