Krogh's principle
Krogh's principle states that "for such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." This concept is central to those disciplines of biology that rely on the comparative method, such as neuroethology, comparative physiology, and more recently functional genomics. History. Krogh's principle is named after the Danish physiologist August Krogh, winner of the Nobel Prize in Physiology for his contributions to understanding the anatomy and physiology of the capillary system, who described it in The American Journal of  Physiology in 1929. However, the principle was first elucidated nearly 60 years prior to this, and in almost the same words as Krogh, in 1865 by Claude Bernard, the French instigator of experimental medicine, on page 27 of his "Introduction à l'étude de la médecine expérimentale": Krogh wrote the following in his 1929 treatise on the then current 'status' of physiology (emphasis added): "Krogh's principle" was not utilized as a formal term until 1975 when the biochemist Hans Adolf Krebs (who initially described the Citric Acid Cycle), first referred to it. More recently, at the International Society for Neuroethology  meeting in Nyborg, Denmark in 2004, Krogh's principle was cited as a central principle by the group at their 7th Congress. Krogh's principle has also been receiving attention in the area of functional genomics, where there has been increasing pressure and desire to expand genomics research to a more wide variety of organisms beyond the traditional scope of the field. Philosophy and applications. A central concept to Krogh's principle is evolutionary adaptation. Evolutionary theory maintains that organisms are suited to particular niches, some of which are highly specialized for solving particular biological problems. These adaptations are typically  exploited by biologists in several ways: