Malaria, the oldest and cumulatively the deadliest of the human infectious diseases, seeped into our very earliest human history. It was a primordial companion of our distant protohuman ancestors and an even earlier companion of the chimpanzees from which we branched off six to seven million years ago. During the last one hundred thousand years, malaria began a new chapter in the human heartland of tropical Africa. As our ancestors clustered in seasonal settlements to fish and gather, mosquitoes found a temporarily less-mobile source of nourishment. This allowed the malaria parasites carried by mosquitoes to infect a growing number of human hosts. From these humble beginnings, malaria became more deeply integral to human history. Malaria eventually traveled with some of our ancestors out of Africa into Eurasia, where new infections took root, even as it percolated more deeply throughout the African continent.

Over tens of thousands of years, as early humanity expanded in tropical Africa and across tropical Eurasia, malaria parasites continued to take advantage of our human propensity to migrate and our social need to congregate. Eventually, the parasites moved with their human hosts into the nascent river-basin communities that would ultimately develop into permanent settlements. Malaria traveled with infected hunters and adventurers across mountain ranges and deserts, and after the domestication of animals, malaria traveled more quickly, galloping across grasslands and plains. It became the principal disease burden of Eurasia as well as tropical Africa.