Malaria due to Plasmodium falciparum is a major selective factor in human evolution .   It has influenced mutations in HBB in various degrees resulting in the existence of numerous HBB variants. Some of these mutations are not directly lethal and instead confer resistance to malaria, particularly in Africa where malaria is epidemic.  People of African descent have evolved to have higher rates of the mutant HBB because the heterozygous individuals have a misshaped red blood cell that prevent attacks from malarial parasites. Thus, HBB mutants are the sources of positive selection in these regions and are important for their long-term survival.   Such selection markers are important for tracing human ancestry and diversification from Africa . 
Side effects tend to be common and occur more frequently with increased age.  The most common adverse reactions associated with benznidazole are allergic dermatitis and peripheral neuropathy.  It is reported that up to 30% of people will experience dermatitis when starting treatment.   Benznidazole may cause photosensitization of the skin, resulting in rashes.  Rashes usually appear within the first 2 weeks of treatment and resolve over time.  In rare instances, skin hypersensitivity can result in exfoliative skin eruptions, edema, and fever.  Peripheral neuropathy may occur later on in the treatment course and is dose dependent.  It is not permanent, but takes time to resolve.