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":

Dans l'investigation scientifique, les moindres procédés sont de la plus haute importance. Le choix heureux d'un animal, d'un instrument construit d'une certaine façon, l'emploi d'un réactif au lieu d'un autre, suffisent souvent pour résoudre les questions générales les plus élevées.

Claude Bernard: Introduction à l'étude de la médecine expérimentale, J.B. Baillière et Fils, Libraires de L'Académie Impériale de Médecine, 1865. pp. 400

Krogh wrote the following in his 1929 treatise on the then current 'status' of physiology (emphasis added):

...I want to emphasize that the route by which we can strive toward the ideal is by a study of the vital functions in all their aspects throughout the myriads of organisms. We may find out, nay, we will find out before very long the essential mechanisms of mammalian kidney function, but the general problem of excretion can be solved only when excretory organs are studied wherever we find them and in all their essential modifications. Such studies will be sure, moreover, to expand and deepen our insight into problems of the human kidney and will prove of value also from the narrowest utilitarian point of view.

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. Many years ago when my teacher, Christian Bohr, was interested in the respiratory mechanism of the lung and devised the method of studying the exchange through each lung separately, he found that a certain kind of tortoise possessed a trachea dividing into the main bronchi high up in the neck, and we used to say as a laboratory joke that this animal had been created expressly for the purposes of respiration physiology. I have no doubt that there is quite a number of animals which are similarly "created" for special physiological purposes, but I am afraid that most of them are unknown to the men for whom they were "created," and we must apply to the zoologists to find them and lay our hands on them."

August Krogh The Progress of Physiology, The American Journal of Physiology, 1929. 90(2) pp. 243-251

"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:

Thermus aquaticus
Tyto alba, the Barn Owl

See also

Further reading

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