Transcribed, by permission, from Tuatara (1984) Vol. 27 (1): 8-13.

Leon Croizat's biogeographic work:
A personal appreciation

By R. C. Craw
Zoology Department, Victoria University of Wellington

Abstract

Leon Croizat's bold and novel attempts to empirically refute Charles Darwin's theory of geographical distribution of organisms by their "means of dispersal", A. R. Wallace's classification of zoogeographic regions, and Alfred Wegener's concept of Pangaea are discussed. Croizat's panbiogeographic methodology and synthesis, and alternative approach to these generally accepted views, is discussed in relation to vicariance cladistic biogeography with which it is often confused.

Keywords: biogeography, cladistics, Croizat, Darwin, dispersal, geology, panbiogeography, vicariance, Wallace, Wegener.

"It may be said, indeed, that Charles Darwin's destiny in life was to watch physical movement physical movement from the stir of an insect in the dust to the explosion of an earth quake all around." So wrote James Hutchinson Stirling, in his little known critique of Darwinism, published in 1894, and relegated to complete obscurity since (Darwinianism, Workmen and Work, Edinburgh, T. & T. Clark). Stirling's critique is philosophical, and heavily coloured by an abstruse Hegelianism, but it is nevertheless perceptive in that it strikes straight at the major weakness of Darwin's theory of evolution by natural selection: the notion that the differentiation of organisms in space and time is a consequence of their originating in specific centres of origin from whence they migrate by means of dispersal, thus to establish their geographic distribution. Darwin's world is a world where organisms are constantly moving, continually pouring forth from specific evolutionary centres that supply advanced and more competitive organisms to other areas of the globe.

There have been many critiques of Darwinism, both before, and after the publication of Stirling's work. Most, if not all, of these critiques focus on the problem of form initially, and argue that natural selection, as conceived by Darwin cannot possibly account for the origin of new structural types of animals and plants. These critiques range from the superb to the indifferent. Some of these critiques like St. George Mivart's On the Genesis of Species, will never be surpassed. But only leon Croizat's critique is unique.

Croizat's criticism of Darwinism is the most fascinating ever published because he chose not to address himself primarily to the problem of form, but rather to the problem of space. For it is through space and in time that the forms of organisms change. Darwin too, of course, thought that biogeography was an interesting subject, for otherwise he would not have introduced "On the Origin of Species" to the world through the medium of this discipline:

"When on board H.M.S. Beagle as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America…" (Introduction to "On the Origin of Species").

And this is Croizat's very point; Darwin knew the importance of the spatial aspect, but failed to capitalize on his initial insights into the problem as recorded in The Voyage of the Beagle when he came to write The Origin (see Croizat, 1964: Space, Time, Form, pp. 592-641).

Croizat thought of doing something that no one had ever thought of doing before, and that no one will probably ever do again. He decided to subject Darwin's theories to an empirical test and posted the question: "Did the geographical distribution of organisms in space and through time, by form support the Darwinian view that means of dispersal, and migrations by these means out of specific centres of origin was the process responsible for geographic distribution?" In order to undertake this massive and challenging experiment Croizat developed his track method of investigation, which enabled him to analyze the geographic distributions of organisms and graph them into what he termed dispersal patterns.

Croizat found these dispersal patterns were rather repetitious and that apparently highly vagile organisms like birds and butterflies exhibited very similar dispersal patterns to extremely sedentary organisms, with no obvious means of dispersal. Such as earthworms and flightless beetles. He discovered that these repetitious patterns, which te hermed standard or generalized tracks, bore no relationship to the present day geographcy of the world, but rather joined areas of the globe what were widely separated; for instance one of his standard tracks crossed the Tasman Sea from New Zealand to Southern Australia/Tasmania, and then drove straight on out over the vast expanse of the Indian Ocean to Southern Africa, while another headed in the opposite direction from New Zealand over the Pacific Ocean to Western South and North America. Various standard tracks were found to overlap with considerable complexity in areas of endemism like New Zealand, and Croizat considered this a major problem of biogeography (Fig. 1).

Of course, the Darwinian answer to this complex pattern of biogeographic area relationships is that present day biota, such as that of New Zealand, have extremely diverse relationships because the means of dispersal of organisms are responsible for the presence or absence of a particular organism in the biota. Each group of organisms in the biota has had a history unique to itself. Biogeography is just telling a 'story': unique narrative explanations are proposed for the historical development of each group studies. But using this approach one can explain everything and anything, and faced by anomalies like organisms with no obvious means of dispersal living on isolated islands, Darwinian biogeographers attribute their presence there to "chance". In contrast to this approach, Croizat suggested that many parts of the world have complex biogeographic relationships because they are biogeographic boundaries.