A reminder of how Raymond Cowles and Charles Bogert changed how the world viewed body temperature regulation in reptiles

An offprint for sale caught my eye. Shortly afterwards I had my first comfortable look at an important piece of research published in wartime USA that I had quoted in my final-year student seminar in February 1965. I say comfortable because all I had then was an incomplete pre-xerox photocopy that was difficult to read. After I read the paper and looked at the photographs, I looked up the authors both in Contributions to the History of Herpetology and on Wikipedia. Showing how appallingly bad many zoologically based articles on the latter are, the most important work of the two authors does not even get a mention.

Raymond Bridgman Cowles (1896-1975) and Charles Michill Bogert (1908-1992) found from their studies of desert lizards that the poikilothermic animals, usually described as ‘cold-blooded’, are  not simply at the same temperature as their surroundings. Instead, by day they use behavioural mechanisms to achieve and maintain a preferred body temperature. When cool they move into, and orientate their bodies towards, the sun. When too hot, they move into shade and/or into burrows. Later, the preferred body temperature of a particular species was shown by Paul Licht to correspond to the optimum temperature for the activity of key enzymes in the tissues.

Cowles and Bogert’s research was enormously influential not only in changing the prevailing views of how poikilothermic animals work but also in opening up a new field of physiological ecology. Indeed Cowles changed the nomenclature.  Poikilothermic (i.e. variable body temperature) was taken to imply that body temperature was not regulated while homoiothermic was the term used for the internally regulated constant body temperature of birds and mammals. He argued that the term ‘ectothermic’ for animals such as reptiles that rely on external sources of heat to maintain their body temperature was more appropriate, with ‘endothermic’ for mammals and birds which generate their own body heat.

Raymond B Cowles
from Contributions to Herpetology
see below

Cowles started the whole thing off. He was born to an American missionary family in South Africa. There, as a boy, he developed an interest in birds and reptiles and back in the USA his PhD thesis was on the life history of the Nile Monitor. Appointed to the University of California at Los Angeles (UCLA) in 1929 he became interested in the extinction of the dinosaurs. He developed the unconventional idea, after seeing the work of two friends on the importance of body temperature on the activity of reptiles at night and on the heat tolerance of lizards and snakes, that dinosaurs were wiped out not by a fall in temperature at the end of the Mesozoic but by a rise. He realised that he should investigate thermoregulation in reptiles both in the field and in the laboratory and to that end established a field station near Indian Wells in 1939.

As well as his work in physiological ecology, Cowles was horrified by the effects of over-population and campaigned vigorously. He saw the effects when he returned in the 1950s to the valley in South Arica where he had lived as a boy. The land was over-grazed, barren and ripe for erosion and flooding. I find astonishing the fact that his trenchant views on the growth of the human population caused him to become unpopular—even a pariah—in his own institution and among the general American public.

Cowles remained at UCLA from 1939 until his retirement in 1962; thereafter he worked at the University of California in Santa Barbara.

Charles M Bogert
from Contributions to Herpetology
see below

Charles Bogert was a student of Cowles at UCLA in the mid-1930s, and like Cowles had wide interests in natural history. By the time he was collaborating with Cowles on thermoregulation in reptiles he was at the American Museum of Natural History in New York. Unable to afford progression to a PhD at UCLA, he had been appointed as assistant to Gladwyn Kingsley Noble in 1936. On Noble’s death at the age of 46 in 1940, Bogert was appointed to head the herpetology department. There he continued the classical ‘museum style’ systematic studies but continued with laboratory and field work in a number of areas, most notably on frog vocalisations and their biological significance. In 1966 UCLA awarded him an honorary LLD. He took early retirement in 1968, continuing to write but a series of strokes from 1988 and severe arthritis debilitated and depressed him. He killed himself in 1992 at home in Santa Fe, New Mexico.

It has been a pleasure reading Cowles and Bogert’s seminal paper which they described as a ‘preliminary study’. It described the first four years of their work  in the Coachella Valley which they described as ‘a desert of extreme heat and aridity, characterized by sporadically abundant annual, and scanty perennial vegetation’. The style of the publication, which appeared in the Bulletin of the American Museum of Natural History, is more discursive than that of a scientific paper with photographs of the terrain, experimental housing and some of the animals they studied.

Much as been added over the 80 years since Cowles and Bogert were busy in the Coachella Valley but some fundamental questions still remain. For example, although some ectotherms may achieve their preferred body temperature for part of the day, they are still poikilothermic—their body temperature does vary over the course of a day. Since temperature affects all chemical processes, then there are implications for such physiological mechanisms as the internal biological clock, for processes like memory and the action of hormones. In addition, questions of ectothermy and endothermy in dinosaurs—the problem that first attracted Cowles to the thermal physiology of desert reptiles—are still a hot topic.

Cowles RB, Bogert CM. 1944. A preliminary study of the thermal requirements of desert reptiles. Bulletin of the American Museum of Natural History 83, 261-296.

Anon. 2014. Cowles, Raymond B (1896-1975). In Contributions to the History of Herpetology (Volume 1, revised and expanded), Edited by Kraig Adler, pp 116-117. Society for the Study of Reptiles and Amphibians.

Anon. 2007. Bogert, Charles M (1908-1992). In Contributions to the History of Herpetology (Volume 2), Edited by Kraig Adler, pp 178-180. Society for the Study of Reptiles and Amphibians.

Turner JS. 1984. Raymond B Cowles and the biology of temperature in reptiles. Journal of Herpetology 18, 421-436.