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The genus Leishmania Ross, 1903 speculations on evolution and speciation

Lack of biological pressures due to the restriction of Leishmania to phlebotomine sandflies and 
mammals of the warmer regions may explain the overall uniformity of the species in their morphology and 
life cycle. The attachment of the « peripylarian » leishmanias, such as L . braziliensis, to the hindgut of their 
sandfly vectors suggests an origin of Leishmania from monogenetic insect flagellates, in the modern 
representativas of which this development is confined to the hindgut. I t is postulated that the primitive 
hindgut development has been lost in the evolution of the « suprapylarian » leishmanias, which are now 
restricted to the mid- and fore-gut. Leishmanial parasites tend to be much more host-restricted than is 
commonly supposed, and the frequent finding of serodeme and zymodeme variants in populations of 
Leishmania species within their recognized geographic distribution is a reflection of on-going speciation.