The fourth edition was issued in 1949 as Freshwater Fishes of the Soviet Union and Adjacent Countries and won him the Stalin Prize.

In the book Berg collected a large amount of empirical data which offered a strong criticism of Darwin's theory of evolution.

[8] Berg's theory of nomogenesis combined arguments from paleontology, zoology and botany to claim that evolution is not a random process.

[9] Berg claimed that the variation of characters in species is confined within certain limits due to both internal and external factors.

The limitation of the variability, Berg argued, left hardly any space for natural selection; he claimed this was supported by the paleontological record because all the phylogenetic branches look more or less like straight lines.

It is connected with the alteration of the fauna of a certain horizon and comes about in certain periods only to be absent for a long time"[10] Thus Berg claimed evolution was caused by mass mutations, which are directed by internal and external factors, so that new species occur with a high probability of being almost perfectly adapted.

According to Berg, newly evolved species beget the subordinate taxonomic categories, and appear to be perfectly adapted to their environments.

They separated shortly after the birth of their second child and though Polina sued, the Russian Orthodox Church granted custody to her Christian husband.

[12] Berg was honored for a lifetime of scientific achievement by the Imperial Russian Geographical Society and presented with the P. P. Semyonov-Tyan-Shansky Gold Medal.