The great man theory is the oldest of the three theories and historically seems to be the most used. It argues that history has been highly influenced by a chain of “great men.” These people stand apart from the crowd when we look back into history; their strength, insight, fortitude and inspiration drove society forward until the next picked up the pieces left by the last and continued on. (Johnson p.42)
The next model used in The Invention of Air is the paradigm shift theory. This theory focuses less on the individual and more on the intellectual era. Paradigms shift when there is too much contradictory evidence that the current theory fails to take into account; exception after exception to the existing model builds up until a new model is presented without the exceptions and eventually takes over. (Johnson p. 47)
The ecosystem theory states that there are many factors at work that prime a time for discovery or stagnation. Each discipline in the sciences, both soft and hard, help to explain a small piece in the larger puzzle that is the global ecosystem, in both the cultural and scientific sense. The ecosystem theory is the newest, and most complicated of the models as it draws on the most factors to explain different events, requiring cooperation between many studies that would typically interact less than is needed to explain historical phenomena. (Johnson p.51-52).
Johnson uses the ecosystem theory most compellingly to explain Joseph Priestly’s discovery of oxygen. He explains that in the ecosystem. Energy is not only in the sense we think of it now, but the agricultural revolution spurred an increase in energy because it allowed food—the primary source of human energy—to be stored. In Priestly’s age the coal deposits he was standing on increased the energy of his society, in that a single person, with the help of machines, could now achieve far more than their predecessor. This allowed for leisure time, which gave Priestly, whose job was religious, not scientific, the time to dabble in science and discover oxygen. This, however, was only a piece of what led Priestly to discover oxygen, alongside it where his biology, geography, culture, aristocratic support, and an amount of luck. The ecosystem approach can also be used to explain other phenomena, such as the literal ecosystem. So much goes into the ecosystem and the ways humans interact with it that there needs to be cooperations between disciplines to explain it. Economists can offer insight into the factors driving pollution, which climatologists can explain the reach that pollution gains, here medical professionals and biologists step in to explain the impact to humans, plants and animals, and economists can again look at those factors to understand a loss in productivity and the negative external effects of loss of loss of biodiversity. This is just one example of how disciplines working together can help us understand the world we live in.