Panbiogeography

In 1964 the biogeographer and evolutionist Leon Croizat published a book titled Space, Time, Form: The Evolutionary Synthesis. The title of the book presented a renewed emphasis on the role and significance of space and time in the evolutionary process and in understanding evolutionary history. Many representations of the theory of evolution from the time of Darwin's On the Origin of Species (1859) assumed that space and [Page 961]time together constituted a separate environmental container through which organisms moved and evolved. Croizat pointed out that this perspective resulted in an erroneous understanding of the evolutionary process.

For most people, time is perhaps the most compelling element of evolution that directly links the present with the past, principally through the geological fossil record. Fossilized organisms are iden-tifiably related to those of the living world, either at a general level of organization or at more specialized levels such as those of genera and species. These fossils have contributed to the idea that living species have a history of ancestral species, some of which are preserved in the fossil record. However, this record alone was not necessarily enough to convince everyone of evolution by descent with modification—including Darwin himself. But it was during his world voyage on H.M.S. Beagle that Darwin found that some fossils in Argentina were more closely related to organisms currently living in that region than to those of other areas. This geographic juxtaposition of temporal records and biological relationships provided Darwin with a critical insight that helped lead him from a creationist to an evolutionary perspective. So it is no surprise that the very first sentence in Darwin's 1859 book began with the observation that the distribution of organisms and the geological relationships of the present to the past inhabitants of South America “seemed to throw some light on the origin of species.”

Darwin's discovery pointed to a key aspect of evolution, that time and space are causally interrelated. But this interrelationship was taken largely for granted in much of evolutionary theory until nearly a century later, when Leon Croizat developed his unique approach to evolution called panbiogeography. In this approach Croizat did what no one else had ever done before. He tested Darwin's theory of evolution through the comparative study of animal and plant distributions, whether living or fossil. Animal and plant distributions provide a direct representation of time and space in evolution. The spatial component is represented by their location, while the temporal component is represented by their differentiation or divergence as well as the spatial correlation of distributions with tectonic features associated with earth history.

In recognizing the integral relationship of time with geographic location and the evolution of biological form, Croizat proposed the representation of evolution as the summation of their individual and combined effects by the following equation: Evolution = space + time + form. This formulation showed that the study of evolution was effectively the study of how all three elements are interrelated and affect each other, rather than just the study of a purely physical (biological) process. Time now becomes part of the evolutionary process rather than just a temporal record of evolutionary events. Because of this integral relationship, Croizat regarded the process of biological evolution (which he referred to as “form-making”) in space over time as fundamental for the whole of biology in both its theoretical and practical aspects.

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