Léon Croizat

Léon Croizat (1964)

Leon Camille Marius Croizat (July 16, 1894 - November 30, 1982) was a French-Italian scholar and botanist who developed a synthesis of evolution of biological form over space, in time, which he named Panbiogeography.

Life

Croizat was the son of French parents, and was born in Torino, Italy, where he studied Law, in spite of his great aptitude for the natural sciences. After obtaining his degree, he concentrated on the sciences, specializing in botany and zoology, studying important aspects of the distribution and evolution of biological species. In fact, he generated a novel current of thought, opposed in some respects to Darwinism, on the evolution and dispersal of biota over space, through time. Between 1936 and 1946, he lived in the United States, where he worked as a technical assistant invited by Dr E. D. Merrill, director of the Arnold Arboretum of Harvard University.

Leon Croizat during the 1950-1951 Franco-Venezuelan Expedition to the sources of the Orinoco River

In 1947, Croizat arrived at Venezuela, invited by the botanist Henri Pittier. He obtained a position in the Faculty of Agronomy of the Central University of Venezuela. In 1951 he was promoted to ordinary professor of botany and ecology in the University of the Andes, Venezuela. Between 1951 and 1952 he participated as botanist in the Franco-Venezuelan expedition to discover the sources of the Orinoco, with Prof. Jose Maria Cruxent. At this time he divorced from his first wife and married his second wife, Catalina, an Hungarian immigrant. In 1953 Croizat gave up all official academic positions to work full time on biological problems. Croizat and his wife lived in Caracas until 1976, when they took over as first directors of the “Jardin Botanico Xerofito” in Coro, a city about 400 kilometers west of Caracas; a botanical garden which they founded and had worked to establish since 1970.

Croizat died at Coro on November 30, 1982 of a heart attack. During his life, Croizat has published around 300 scientific papers and seven books, amounting to more than 15,000 printed pages. He was honoured by Venezuela with the Henri Pittier Order of Merit in Conservation, and by the government of Italy with the Order of Merit. Several plant and animal species have been named after Croizat.^[1][2][3]

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 ^[5]

In graph theory a track is equated to a minimum spanning tree connecting all localities by the shortest path.^[6]

To explain disjunct distributions, Croizat proposed the existence of broadly distributed ancestors that established its 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",^[7] which refers to the fact that a variation in form is limited and constrained.^[8] 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 as one of biogeographic concern.

Although authors belonging to the dispersalist establishment have dismissed Croizat’s contributions, others have considered 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. Panbiogeography became established as a productive research programme in historical biogeography ^[9]

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
• Croizat L. 1982. Vicariance/vicariism, panbiogeography, "vicariance Biogeography," etc.: a clarification. Systematic Zoology 31: 291-304.

References

Further reading

• Morrone J.J. (2004). Homología Biogeográfica: las Coordenadas Espaciales de la Vida. México, DF: Cuadernos del Instituto de Biología 37, Instituto de Biología, UNAM.
• Morrone J.J. (2007) La Vita tra lo Spazio e il Tempo. Il Retaggio di Croizat e la Nuova Biogeografia. M. Zunino (Ed.). Palermo: Medical Books.
• Nelson, G. (1973). Comments on Leon Croizat's Biogeography. Systematic Zoology. Vol. 22, No. 3. pp. 312-320.
• Rosen, D. (1974). Space, Time, Form: The Biological Synthesis. Systematic Zoology, Vol. 23, No. 2. pp. 288-290.

External links

• Heads, M. & Craw, R. (1984). Bibliography of the scientific work of Leon Croizat, 1932-1982. Tuatara 27: 67-75
• References on Panbiogeography
• Croizatia. Revista Multidisciplinaria de Ciencia y Tecnología
• Video documentary on Croizat