Perspectives on Life and Respiration: How, When, and Wherefore
Humankind has always been fascinated by the spectacle of extreme states and phenomena. The Guinness Book of Records, which after the Holy Bible is alleged to be the second most widely read book, is according to the publishers compiled “in hope of providing a means for peaceful setting of arguments about record performances”. Though not given much attention outside the professional realms, the elegance and constellation of life on Earth is enchanting, bewildering, and intellectually intriguing. More than 284 000 species of plants, 750 000 species of insects, and 280000 species of other animals have been catalogued (e.g., Dixon 1994; Service 1997). Of this plethora, vertebrates represent only one phylum and a mere 50000 species or so (e.g., Pough et al. 1989). Nature’s fortitude for survival is remarkable. For example, albeit the tumultuous crises which preceded the Tertiary period when colossal population clashes occurred and many species were wiped out, by the end of the period, there were as many as 2500 families of animals (Benton 1995). From molecular sequence studies of different microcosms (e.g., Pace et al. 1985; Ward et al. 1990; Winker and Woese 1991; Olsen and Woese 1993), it is becoming unequivocally evident that, compared with the Metazoa and the Metaphyta (i.e., the visible world), the microbial domain (i.e., the microworld) presents a more complex biodiversity than was hitherto thought, and quantitatively remains largely unknown to us (e.g., Embley et al. 1994; Lovejoy 1994). The existing numerical data on the taxonomic diversity of animal life differ remarkably. It is envisaged that life’s copious tree comprises between 5 and 50 million species of animals (e.g., May 1988, 1990, 1992; Hammond 1992).
CitationThe Gas Exchangers pp 1-51
Springer Berlin HeidelbergFaculty of Veterinary Medicine Dept. of Veterinary Anatomy, University of Nairobi