The Survival of Animals in Hot Deserts’ 
By E. B. EDNEY 
Professor of Zoology 
University College of Rhodesia and Nyasaland 
Salisbury, Southern Rhodesia 
My arm in this lecture is to consider the difficulties which confront 
animals living in hot dry environments, and to try to answer the 
question as to why some animals are more successful than others in 
overcoming them. The problems for all are the same: how to prevent 
desiccation and how to keep cool. But the solutions are various, and 
depend upon the morphological and physiological equipment of the 
animals concerned. 
The process of keeping cool may involve loss of water. But water 
in hot climates may be in short supply, and in any case water loss is 
necessarily incurred in such vital processes as respiration, excretion, 
lactation (in mammals), egg production, and so forth. A conflict is 
therefore immediately apparent between the necessity to conserve 
water for vital processes and to transpire water for cooling. It will 
be part of my purpose to see how these opposing needs are brought 
into equilibrium in different kinds of animals. 
Now the problems confronting animals in hot deserts are essentially 
the same as some of the problems experienced in a less acute form by 
all terrestrial animals during their evolution from water to land life. 
We must therefore see the former problem in a wider setting, and take 
the discussion in two stages. First, we may review, in fairly general 
terms, the problems of terrestrial life, and note how different groups 
of animals have tackled them. Second, in the light of this informa- 
tion, we may consider in greater detail the solutions of the more acute 
problems posed by extreme terrestrial conditions. 
There have been major invasions of the land by three great phyla 
vertebrates, arthropods, and mollusks—as well as minor invasions by 
other animals such as flatworms and annelid worms. Within the 
arthopods there has certainly been more than one invasion. Insects 
and spiders probably emerged separately; crustaceans certainly 
1Inaugural lecture given in the University College of Rhodesia and Nyasaland. Re- 
printed by permission of the College and the Oxford University Press. 
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