León Croizat

Léon Camille Marius Croizat (16 July 1894 – 30 November 1982) was a French-Italian scholar and botanist who developed an orthogenetic synthesis of the evolution of biological form over space, in time, which he called panbiogeography.

Life Croizat was born in Torino, Italy to Vittorio Croizat (aka Victor Croizat) and Maria (Marie) Chaley, who had emigrated to Turin from Chambéry, France. Several plant and animal species (and one genus) have been named after Croizat.

Concepts

Panbiogeography is a discipline based on the analysis of patterns of distribution of organisms. The method analyzes biogeographic distributions through the drawing of tracks, and derives information from the form and orientation of those tracks. A track is a line connecting collection localities or disjunct areas of a particular taxon. Several individual tracks for unrelated groups of organisms form a generalized ('standard') track, where the individual components are relict fragments of an ancestral, more widespread biota fragmented by geological and/or climatic changes. A node arises from the intersection of two or more generalized tracks

In graph theory a track is equated to a minimum spanning tree connecting all localities by the shortest path.

To explain disjunct distributions, Croizat proposed the existence of broadly distributed ancestors that established their range during a period of mobilism, followed by a form-making process over a broad front. Disjunctions are explained as extinctions in the previously continuous range. Orthogenesis is a term used by Croizat, in his words "... in a pure mechanistic sense", which refers to the fact that a variation in form is limited and constrained. Croizat considered organism evolution as a function of time, space and form. Of these three essential factors, space is the one with which biogeography is primarily concerned. However space necessarily interplays with time and form, therefore the three factors are one of biogeographic concern. Put another way, when evolution is considered to be guided by developmental constraints or by phylogenetic constraints, it is orthogenetic.

Some researchers consider Croizat as one of the most original thinkers of modern comparative biology, whose contributions provided the foundation of a new synthesis between earth and life sciences.

While some biologists have continued to apply panbiogeographic approaches, and as having "fallen by the wayside" in 2023. Robert H. Cowie, writing in a book review in Heredity stated "Panbiogeography seems to me at best to offer little new insight, at worst to be fundamentally flawed" criticising panbiogeographers for not placing enough emphasis on phylogenetics, which Cowie states is "the underpinning of any biogeographical analysis".

Selected works Manual of Phytogeography or An Account of Plant Dispersal Throughout the World. Junk, The Hague, 1952. 696 pp. Panbiogeography or An Introductory Synthesis of Zoogeography, Phytogeography, Geology; with notes on evolution, systematics, ecology, anthropology, etc.. Published by the author, Caracas, 1958. 2755 pp. Principia Botanica or Beginnings of Botany. Published by the author, Caracas, 1961. 1821 pp. Space, Time, Form: The Biological Synthesis. Published by the author, Caracas, 1964. 881 pp