GUNS, GERMS AND STEEL - Cloverport Independent Schools

4 2 2 • EPILOGUE
must gain knowledge in these historical sciences by other means, such as
observation, comparison, and so-called natural experiments (to which I
shall return in a moment).
Historical sciences are concerned with chains of proximate and ultimate
causes. In most of physics and chemistry the concepts of "ultimate cause,"
"purpose," and "function" are meaningless, yet they are essential to
understanding living systems in general and human activities in particular.
For instance, an evolutionary biologist studying Arctic hares whose fur
color turns from brown in summer to white in winter is not satisfied with
identifying the mundane proximate causes of fur color in terms of the fur
pigments' molecular structures and biosynthetic pathways. The more
important questions involve function (camouflage against predators?) and
ultimate cause (natural selection starting with an ancestral hare population
with seasonally unchanging fur color?). Similarly, a European historian is
not satisfied with describing the condition of Europe in both 1815 and
1918 as having just achieved peace after a costly pan-European war.
Understanding the contrasting chains of events leading up to the two peace
treaties is essential to understanding why an even more costly pan-European
war broke out again within a few decades of 1918 but not of 1815.
But chemists do not assign a purpose or function to a collision of two gas
molecules, nor do they seek an ultimate cause for the collision.
Still another difference between historical and nonhistorical sciences
involves prediction. In chemistry and physics the acid test of one's understanding
of a system is whether one can successfully predict its future
behavior. Again, physicists tend to look down on evolutionary biology
and history, because those fields appear to fail this test. In historical sciences,
one can provide a posteriori explanations (e.g., why an asteroid
impact on Earth 66 million years ago may have driven dinosaurs but not
many other species to extinction), but a priori predictions are more difficult
(we would be uncertain which species would be driven to extinction
if we did not have the actual past event to guide us). However, historians
and historical scientists do make and test predictions about what future
discoveries of data will show us about past events.
The properties of historical systems that complicate attempts at prediction
can be described in several alternative ways. One can point out that
human societies and dinosaurs are extremely complex, being characterized
by an enormous number of independent variables that feed back on each
other. As a result, small changes at a lower level of organization can lead