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Perspectives in Biology and Medicine 43.2 (2000) 243-251

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On The Significance of a "Minor" Phylum (The Tardigrada) in the Context of a Constructivist View of Knowledge

Ian M. Kinchin *

The tardigrades--also known as "water bears" or "moss piglets"--are microscopic invertebrates (typically 100 to 500µm long). They exhibit a unique anatomy and so have been designated as a discrete phylum in their own right. Tardigrades are found in a wide range of aquatic habitats (both freshwater and marine), with many found in temporary bodies of water, such as those held in cushions of moss or in soil. Most of the tardigrade species, which inhabit such unpredictable environments, are able to tolerate total desiccation by replacing the water in their bodies with an inert sugar (trehalose) in order to maintain cellular integrity. Such desiccated animals are resistant to environmental extremes and can remain viable for several years. This has generated interest among those who would like to apply this technique to other biological systems that might benefit from dry storage in extreme conditions (e.g., storage of live vaccines in parts of the world where refrigeration is not an option).

Though tardigrades have been known for over 200 years, their small size and benign nature means that few observers happen upon them by accident. As a consequence, only about 800 species have been described world-wide, though this number continues to grow at a steady rate. Those who have studied tardigrades know these animals as a source of delight and fascination. Their strange anatomy and remarkable physiology have provided researchers with numerous questions since their discovery--many of which still remain unanswered despite the efforts of an active and dedicated global research community. However, the Tardigrada has often been considered as a relatively unimportant group of invertebrate animals, representing no immediate medical, agricultural, or economic significance. With [End Page 243] such a recommendation, it is not surprising that major funding for research into the biology of these animals is rare. However, despite this unpromising background, this was the group upon which I chose to carry out my own postgraduate research. In an article that reviewed the literature concerning the origins and affinities of the phylum [1], an attempt was made (perhaps prematurely) to address the deceptively simple question that had been asked of me by numerous colleagues: "What is a tardigrade?" The arguments presented were largely based on interpretations of structural and histochemical studies of tardigrades (often made by authors who were really more interested in other invertebrate groups), on a comparative basis in the light of similar observations of various aschelminths 1 and/or arthropods. The conclusion drawn was that the tardigrades (one of the smallest animal groups) were probably more closely related to the arthropods, the biggest group of all. The same question was subsequently given prominence in the first chapter of a book, which summarized the state of knowledge of this group and provided a modern literature review [2]. Some of the tentative suggestions made therein have subsequently been explored more thoroughly by others in various detailed studies, including some in which the authors have used sophisticated investigative techniques which had previously not been applied to the tardigrades. These are reviewed below and set in the context of the current "nature of science" debate which occupies so many pages in the science education journals. While many "traditional" scientists may not agree with alternative views of science, they should be aware of the debate and its possible consequences.

The Nature of Knowledge

Sir Isaac Newton eloquently summarized a widespread view of science as a "great ocean of truth, waiting to be discovered" [quoted in 2]. Such a traditional view holds scientific facts as unshakeable truths which are simply awaiting discovery. This objectivist view of knowledge, or epistemology, is taken for granted by many in the sciences, though critics would argue that such a search for truth is no longer a viable position and can be likened to the quest for the Holy Grail...


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