What made you pick your first choice, Medieval Technology and Social Change?

My graduate education was largely focused on the social and political history of Europe. It is only after I got my PhD that I encountered much broader aspects of history. Unlike many historians, who tend to specialise in a narrowly focused area of history, I have become ever more interested in broadening my view of history to encompass the power of technology and the relations between humans and the rest of nature.

This was the first book that called my attention to a new field of history. It opened my eyes to the role of technology in human affairs. Until then, my interest in technology had been purely instrumental – how to fix a bicycle, how an airplane stays up in the air, and so on. White’s book showed me that technology – the means by which humans use resources for their own ends – was one of the most important, though neglected, aspects of history, one that explained how some people were able to thrive in places where others had failed.

I hadn’t realised the importance of technology in human affairs until I read this book. One good example is when he talks about the invention of stirrups for horse riders, which is the metal bit that they put their feet through to keep them stable. This happened in the eighth century, and it meant that they were more agile in warfare because they could still stay on the horse even when they were pushed by a spear from an opposing rider. This transformed mounted cavalry warfare. Also the introduction of a horse collar in the early Middle Ages made the horse infinitely more useful in agriculture. So it was technology making the horse more powerful and useful.

Today many people think of technology as computers and the Internet, but really technology means those devices that humans have invented to make it possible to do things they couldn’t do otherwise – and that could be as simple as the horse collar or a stirrup.

Tell me about your next book, Plagues and Peoples by William McNeill.

I had long known of McNeill’s work as a world historian. In Plagues and Peoples, he showed that humans were not only vulnerable to a force of nature – disease – but that their actions and ways of life made them more so. He looks at how diseases became much more prevalent, how they spread widely.

In Roman and Greek times, diseases were transported with people as they moved from one place to another. A key moment in the history of mankind is the spread of diseases across Eurasia during the Middle Ages. For me, perhaps the most important example of the spread with human interaction is the diseases that the conquistadores brought with them from Europe to Mexico. Many of the people of the Americas were wiped out by those diseases.

In short, this book opened my eyes to the relationship between humans and the rest of nature. Most history books deal with interactions amongst humans, with a passing mention of the weather or the oceans, which are seen as barriers to human interaction. What this book does is bring the role of natural forces – not just diseases – to the forefront and show how, despite what we think of ourselves, we really are a part of nature and vulnerable to the forces of nature. At the same time, we are not just passive victims of natural forces but we have greatly influenced these forces, as in the case of diseases. We are the ones who spread diseases which were once local to the rest of the world. I think that diseases and natural forces are an essential part of understanding world history. And that is what turned me from a political and social historian into an historian of technology and the environment.

Your next book, Alfred Crosby’s Ecological Imperialism, continues this theme of the environment.

Alfred Crosby is a well known environmental historian. He became famous with a book called The Columbian Exchange, which deals with the spread of animals, plants and diseases between the Americas and the old world. What he does in Ecological Imperialism is take that idea one step further and show how environments influenced the relations between civilisations, especially between Europe and the new world – and how, in turn, contact between the old world and the new changed environments around the world.

He shows how Europeans have established what he called “neo-Europe”, such as North and South America, Australia and New Zealand. In taking over those parts of the world, they changed the population from indigenous to European. He says that was done not by warfare so much as by the introduction of plants, animals and diseases. In North America, much of the food and most of the domesticated animals that we have, and the diseases that infect us, are almost all imported from Europe or the Eastern Hemisphere. Technologies were extremely important because they involved transplanting plants and animals.

Some would argue that this movement has been very damaging in many ways for the environment and people of those places.

The damage for some people is a benefit for others. For the great majority of North Americans, it has been a boon. The same goes for the people of the Eastern hemisphere, who obtained a number of plants from the Western hemisphere in exchange.