Mosaic Evolution of Subterranean Mammals: Regression, Progression and Global Convergence
- Eviatar Nevo
Across the globe, at least 285 of 4,629 species of mammals, representing 11 families, spend most of their lives in moist, dark, oxygen-poor and carbon-dioxide-rich burrows, deprived of most of the sensory cues available above ground. These mammals have become fully specialized for a unique way of life in which foraging, mating and breeding take place underground.
Although most subterranean species have been known to scientists for a long time, their biology has remained largely unstudied. This may be explained by their cryptic way of life and the related problems of keeping, breeding and monitoring them, and also by the fact that scientists tend to be more attracted by animals confronting environments and problems above ground that seem far more complex than those encountered below ground (sensitive vision compared with blindness, echolocation compared with human-like hearing, long-distance navigation/maze orientation across tens of metres, thermoregulation in the cold/life in a thermally buffered burrow). Although many specimens of moles (insectivorous subterranean mammals) and mole-rats (subterranean rodents) have been deposited in museums, not even the morphology of their digging specializations has received the attention it deserves. The convergent evolution of subterranean mammals, one of the most remarkable examples of convergence, is rarely mentioned in textbooks.
The ‘sleeping beauty’ of subterranean mammals, and their importance for science, has been awoken by Eviatar Nevo of the University of Haifa, Israel. His contribution to the growth of our knowledge of subterranean mammals has not only inspired others; he has himself co-authored at least 20 per cent of all published studies.
Growing knowledge, and the landmark dates of Nevo's major contributions (1969, 1979, 1989), seemed to predestine 1999 as a further important year, and the time was right for his book to appear. Undoubtedly, Nevo is the most competent person to write it. And the expected monograph, which went unpublished for several decades, has at last appeared.
The book describes and analyses the 40 million years of global evolution of subterranean mammals and its implications throughout biology. Although the underground habitat is in many respects relatively simple, monotonous, stable and predictable, it is in others very specialized and stressful. Consequently, the evolution of subterranean mammals involves dramatic and complex adaptive structural and functional changes that are both regressive (degenerative) and progressive (compensatory). This mosaic convergent global evolution of subterranean mammals is an example par excellence of comparative studies in evolution at all organizational levels, from the molecular to the organismal, oriented by natural selection.
The book is filled with information. The reader will find not only an up-to-date overview of subterranean mammals and their evolutionary problems, but also detailed information and references to general aspects of sensory and behavioural ecology, morphology, physiology, genetics and immunogenetics. This is all based on Nevo's 50 years of studies and experience, and on careful, critical and thoughtful study of hundreds of articles and books. The book provides excellent texts for seminars and courses. It is richly illustrated, and there are more than 1,800 entries in both the index and the well-balanced bibliography. The book is a ‘must’ for all students of subterranean mammals, and will be very useful to evolutionary biologists.
Considering the hitherto catalytic effects of Nevo's work, I would like to bet that the number of studies dealing with subterranean mammals will rise dramatically in the coming years (indeed, there is great potential for surprising discoveries), and that there will quickly be a need for a second edition. No doubt, subterranean mammals will soon be burrowing their way into the textbooks of the future.