01 February 2011

Humboldt, Bergmann, and Haeckel: The German Roots of Ecology

One of the axioms of science is that any report on your research should include a thorough overview of the topic it addresses. This often means that introductions to scientific papers include some very old citations (for some authors, trying to find the oldest publication you can legitimately cite has become a game, and a pretty fun one at that). I'm in the process of writing the first chapter of my dissertation on the influence - or lack thereof - of climate on body size evolution in mammals, which turns out to be a very long-standing area of study. In working back to the roots of the debate, I've found myself returning to three papers from the early to middle 19th Century, one of which has a direct bearing on my research, another that is a little more tenuously connected, and a third that is only indirectly related but has a profound impact on everything I study. These papers were written by three very different scientists who were studying very different groups of organisms, but all three papers share one major commonality and, as I hope to convince you, several smaller ones as well.
The most recent of these publications is Haeckel (1866): Generelle Morphologie der Organismen by Ernst Heinrich Philipp August Haeckel. Haeckel is remembered today for many things; some of these are positive (he was continental Europe's most eloquent and effective supporter of Darwin and one of the most accomplished scientific illustrators of all time) and some of them very, very negative (he used evolution and his studies on development to justify scientific racism), but he makes an appearance here because it was in his 1866 book that he introduced the word 'ecology' to the world. Haeckel defined his newly-minted word (which roughly translates as 'house study' in Greek) as the study of the environments of organisms. In modern popular culture, environment is often taken to mean the group of abiotic factors - variables such as climate, geography, and geology - that influence an organism, but to ecologists, this is only half the story; organisms also interact with a biotic environment shaped by factors such as predation, competition, and productivity. Ecology, then, is the study of how biotic and abiotic variables influence organisms or, more simply put, the study of why organisms evolve (as opposed to how life has evolved and is evolving, the province of evolutionary biology, though of course there is a huge overlap between the two fields). Because he coined the term, Haeckel is often thought of as the father of ecology, but in fact he would have had no field to provide a name for had it not been for the work of earlier scientists studying the influence of environment on evolution.
One of the most influential of these proto-ecologists was Karl Georg Lucas Christian Bergmann, whose work forms the backbone of my dissertation and of countless other research projects over the course of the last century and a half. Very little biographical information is available for Bergmann: the salient points are that he was born in 1814, attended the University of Göttingen, taught at both his alma mater and at Rostock, and died in 1865, one year before Haeckel wrote his landmark book. While at Göttingen in 1847, Bergmann published the paper for which he is best remembered today: Über die Verhältnisse der Wärmeökomie der Thiere zu ihrer Grösse. The title is a bit of a tongue twister for non-German speakers, but the concept is straightforward enough. Bergmann observed that species of mammals (not individuals within species, as is commonly thought) that lived near the poles tended to be larger than those living towards the equator. Bergmann's explanation for this was that large mammals have small surface area to volume ratios and can therefore retain heat more easily while, conversely, small mammals can shed heat more effectively. Naturally, the poles are colder than temperate regions which are in turn colder than the tropics, and therefore as you head from the former to the latter, you should expect to see a decrease in body size. Bergmann's rule, as this hypothesis has come to be known, has been put to the test several times; his relatively simple explanation has been both supported and attacked by ecologists through the years, but regardless of what you think of his rule, it can't be denied that Bergmann was a pioneering ecologist. By assigning a physical cause to a biotic pattern - and eleven years before Darwin and Wallace introduced the world to natural selection, no less - Bergmann set the tone for generation of ecologists to follow, and as such he deserves to be remembered as a father of the field.
If Bergmann is one of the fathers of ecology, then surely its grandfather was Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt (1769-1859). As opposed to the relatively obscure Bergmann and the politically distasteful Haeckel, Humboldt is one of the best-known and most beloved figures in the history of science; his Latin American travels and research garnered praise from such luminaries as Edgar Allen Poe, Simon Bolivar, and Thomas Jefferson (himself a scientist of no little reputation) and would inspire Darwin's voyage on the Beagle. While it was his travel narrative that would establish his fame, Humboldt also laid the cornerstone of ecology when, along with his traveling companion Aimee Bonpland, he published Essai sur la géographie des plantes in 1805.  During his sojourn in South America, Humboldt had climbed the volcanic peak of Chimborazo in the Ecuadorian Andes (though he failed to reach the summit) and was struck by the distinct zones of vegetation he encountered during his ascent.  His notes, coupled with observations of similar patterns on European mountains, gave Humboldt the data necessary for his 1805 paper as well as the large-scale figure that accompanied it (itself a milestone of scientific illustration).  By tying vegetation to factors such as temperature, air pressure, and soil type Humboldt became the first scientist to seriously study the influence of the environment on organisms, earning his reputation as a pioneering ecologist as well as countless citations in manuscripts (including mine) over the course of the subsequent two centuries.
The authors of these three papers no doubt had many things in common, but perhaps the most striking is that they shared a country of origin.  At first glance, it seems illogical that ecology should have been born in Germany (which, after all, was only a collection of smaller kingdoms and principalities until 1871).  Germany has always produced great scientists, from Leibniz to Einstein, but in Humboldt's time Paris was the center of the scientific world, and many of the most celebrated accomplishments of 19th Century science took place not on the Continent but across the English Channel.  Even within biology, France and Britain played a dominant role, producing some of the greatest anatomists and, later, evolutionary biologists that have ever lived.  Nonetheless, ecology was, at its root, a uniquely German phenomenon.  This begs a rather obvious question: why?  While I'm a far better paleontologist than historian, I think think I have the glimmer of an answer, but in the interest of keeping unassailable historical facts apart from more baseless arm-waving, I'll save my thoughts for a later post.  Stay tuned...

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