[Properties of norm and variability]

Data of the authors from many years on the two ways of development of a group of offspring of tailless amphibians--development with the effect of the norm of characteristics and development with the effect of mass anomalies of a number of characteristics--are summarized. Mass anomalies of limbs in the African clawed frog Xenopus laevis were obtained in laboratory (without using any special influences). They represent a syndrome when the structure of limbs and their girdles, as well as the sacral part of the spine, change correlatively. The syndrome has several stages of manifestation (according to the degree of intensification of deviations from the norm). The maximum manifestation of the syndrome produces a change in the norm of the structure of the sacral part. It was shown that change in the rule of its variability precedes change in the norm of the structure of the sacrum. Not having an opportunity of observing the process of evolution directly (change in norms on the large scale of time), we have to use any data (even indirect), which can give us information on how the change in the norm takes place and what happens to the variability.