From p. 55 of Jonas Stadling’s Through Siberia (1901):
… the Russian settlers here [in Buryatia] have to a great extent been “Buriatised”, as the Russians in Yakutsk have been “Yakutised”. This is to be seen not only in physical changes of the Russian type — the dark colour of hair, eyes, and skin, and the Mongolian or Tatarian facial traits characterising the old Russian population in Siberia — but also in their habits and ideas. Thus, both here and in Yakutsk, the old Russian settlers and their descendants have forgotten their mother-tongue, and speak only the Buriat and Yakut languages, or some kind of mixed tongue. Their Russian orthodoxy has also become very much weakened, many of them cherishing stronger faith in the powers of the Shaman than in the ceremonies of the Russian priest.
All of these aspects of metamorphosis through admixture and prolonged proximity are also to be seen amongst the blancos and brancos of Latin America, but rarely to so dramatic an extent. Why is this so?
Stadling echoes Yadrintseff’s harsh judgment on the roughness and low civilizational quality of the conquerers of Siberia — the trappers and the Kossacks — and those that followed in their footsteps (pp. 285), deeming them criminals, slaves, and rapacious adventurers. The fairness of that characterization aside, he does point out what would seem to be a serious Russian disadvantage in culture-transmission: Not only the common people among the Russian colonists, but also the priests were illiterate. I have elsewhere pointed out the fact that even to-day illiteracy — e.g. among the Buriats — is much less than among the peasantry in European Russia. It is therefore no wonder that the Russian colonists easily forget their native tongue and adapt the language, manners, and superstitions of the natives… (p. 287).
But it seems obvious that a purely numeric factor is also at play here: Buryats and Yakuts, at least, did not suffer any irrecoverable demographic collapse upon the introduction of Russian disease; in fact, their ranks burgeoned considerably during Russian rule. (Resilience in the face of zoonotic epidemic disease probably owes much to these groups’ history of stock-breeding and ought not be construed as typical for the natives of Siberia or the Russian Far East — look, for one instance among many, to the experience of the Yukaghirs.)
Stadling, J. (1901). Through Siberia. (F. Guillemard, Ed.). Westminster: A. Constable & Co.