Nomothetics and idiography in developmental biology.

Successions of space-temporal structures arisen during development of multicellular organisms are the most regular, complex and reproducible ones among all taking place in the entire nature without a human's intervention. Therefore, the question whether it would be possible to embrace them by a common physicalistic law (nomothetic approach) or they can be only enumerated and described one after another (idiography) is of an overall importance for the natural sciences in general. We review several nomothetic attempts performed in XX century biology and suggest that such laws may have a structure of feedback contours between the active and passive mechanical stresses generated in developing embryos. We trace several steps towards creating such contours and show that they couple mechanics with geometry providing thus a progressive complication of embryonic structure. Then we discuss, in what way genome can influence these morphomechanical laws. We speculate that the main developmental function of genome is to set up the values of the parameters, introduced in these laws. We emphasize that these parameters values acquire a definite meaning only within the context of the laws into which they are introduced.