Figure 4
A map of the approximate area dwelled by Akha and Lahu54, represented by the rectangle, illustrating a hypothetical scenario of M. tuberculosis L2 evolution. The map was adapted from a public template (https://commons.wikimedia.org/wiki/File:Mainland_Southeast_Asia.png), using Google Slide (https://docs.google.com/presentation). As L2.1, the most basal sublineage of L2 was most common in Guangxi, the origin of L2 may be there. Subsequently, L2 strains might have spread to the mountainous areas on the west of Guangxi, and diversified to become L2.2 and L2.2.1/Ancestral strains. The strains circulated among various ethnic groups. The harsh terrain and alternate high mountains and valleys running mostly from North to South support a highly diverse species adapted to different latitudes and altitudes and allow societies with different cultures and languages to thrive, presumably with minimal genetic admixing for a prolonged period of time. This might have allowed for the diversification of L2.2.1, each of which co-evolved with a different ethnic group. Potentially facilitated by the Ancient Tea Horse Road or Southwest Silk Road45, some of the bacteria might have eventually been transmitted to a much larger and denser population of Han Chinese and further evolved to become the current Modern Beijing strains. Some of the minority tribes migrated to the South carrying some sublineages, such as L2.2.1.Ancestral 4 and L4.5.2, with them.
