(biol.), the average for the form (population) probability of retaining
the organisms of each generation and their participation in the
reproduction of form. V. measure with the ratio of the number of
adult individuals, who participate in the multiplication, to the
number of those bearing in each generation (or to the number of
postponed eggs, vymetannykh roe corns, ripened seeds, etc.). It
is lowered with the unfavorable conditions v. (as fruitfulness), the
number of population falls; it grows with the favorable
conditions, producing stabilization or increase in the number of
population. In the course of progressive evolution v. it grows
by many orders. Thus, sr. V. of organism with 10-7-10-6% in bacteria, unicellular animals and plants rises to
10-30% in the highest animals. This is connected with the
development of a number of the systems, which facilitate increase in
the reliability of organism and reduction in the losses on all phases
of ontogenesis (development of multicellularity, differentiation of
organs, the improvement of self-adjustment and homeostasis, an increase of the quantity
of yolk in the egg, passage k vnutr. to fertilization, to viviparity,
the active concern about posterity, etc.). Increase in the
course of evolution v. is accompanied by a regular drop in
fruitfulness. Thus, in animals with the small and poor by yolk
eggs, edged directly into the water, females put aside one time many million eggs, and in it is
specific with well the protected large eggs and capable to guard young
- only of 10-100 eggs. The retention by optimum v. is important
for the process of evolution, since its further increase can
dangerously decrease the effectiveness of natural
selection and the evolutionary plasticity of form.
With action research on the organism of different
unfavorable factors (for example, the ionizing emissions) they also
use term "v.", designating by it the percentage of the survived
organisms. K. M. Zavadsky.
