Abstract <p>The plague microbe (<i>Yersinia pestis</i>) is unique in the family of pathogens of intestinal infections of the family Yersiniaceae (Enterobacteriaceae) and the genus <i>Yersinia</i>. This is the only species of the family and genus that, in natural conditions, is transmitted in rodent populations not by an alimentary route, like typical intestinal pathogens, but through flea bites, which indicates some unique circumstances of its speciation. One such special circumstance was the wound infection in populations of the Mongolian marmot (<i>Marmota sibirica</i>), with the causative agent of pseudotuberculosis of the first serotype (<i>Y. pseudotuberculosis</i> O:1b) or, in other words, Far Eastern scarlet-like fever (FESLF). The abiotic trigger for speciation was the maximum Sartan cooling, which covered vast areas of Central Asia at the turn of the Pleistocene and Holocene, 22 000–15 000 years ago. Deep freezing of the ground in the settlements of the Mongolian marmot led to a change in the behavior of the larvae of the marmot flea <i>Oropsylla silantiewi</i>—a transition to hematophagy on marmots during hibernation, which caused a massive penetration of the FESLF pathogen into the blood of marmots through wounds on the mucous membrane in the oral cavity, created by flea larvae. Aberrant resistant wound infection of marmots with FESLF changed the gene flow and speciation of <i>Y. pestis</i>. According to the optimistic version of the environmental scenario, the speciation process took place autonomously in three geographical populations of marmots; almost simultaneously, three initial microbial subspecies, 2.ANT3, 3.ANT2, and 4.ANT1, appeared, which later became the basis of the entire world intraspecific diversity of this pathogen.</p>