Malaria has been an extraordinary shaper of history. Dated as far back as 30 million years old, this protoza really took off after the agricultural revolution (not surprising, since it thrives in mosquitos, who love the standing waters that frequently accompany cleared out lands). Some scientists believe Malaria to be the single-biggest killer in human history. The warm and tropical climate of central Africa has been so continuously impacted by the mosquito-born disease that natural selection actually fostered the inherited genes causing sickle-cell anemia among humans from this part of the world. (See second photo.) Although the dominant genetic expression of sickle-cell anemia has led to early mortality, in its recessive form resistance to Malaria can be conferred. (See third image: HbAS is the sickle-cell gene.) Scientists aren’t certain about the mechanics of how the resistance works, although they think it might starve the Malaria protozoa from oxygen in a certain point in its life cycle. Regardless, the genetic evolutionary response to Malaria has been a boon and a curse historically for those from central Africa, even aside from the immediate health effects. In the 1700s in the Mid-Atlantic region of North America, because the white settlers and American Indians died so frequently from an increasing rate of Malaria (caused by the clearcutting and newly swampy lands of plantation farming), the hardiest slaves to be found were from Central Africa. Thus, the creation of a slave system linked to race became an entrenched part of American history. On the other hand, the prevalence of Malaria protected much of the African continent from colonization by Europeans until the development of anti-Malaria medications became effective. (The last photo is of the cinchona tree, whose bark produces quinine, a critical anti-Malaria agent.)
