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Historically, Africans faced significant environmental challenges that limited population growth. There are exceptions, but overall, African soils are poor and rainfall has been unpredict-able. Soils are comparatively unfertile, due in part to the geologic age of the continent. Also, the more temperate climates in a number of regions slows the decomposition of organic materials in the soil, meaning that the soil in many regions has few minerals and nutrients. The areas that are exceptions, such as the highlands of Ethiopia, Rwanda, and Burundi, have seen much higher population concentrations. Rainfall also tends to be concentrated in just two or three months a year, while disease has been yet another challenge.
Considering the past 5,000 years of African history, malaria, yellow fever, and trypanoso-miasis (also known as sleeping sickness) have made the biggest impacts on population growth and settlement patterns. Even today, all three diseases affect the continent. Both malaria and yellow fever are spread to people by mosquitos. According to the World Health Organization (WHO), despite preventative measures and great efforts to extend the availability of treatments, malaria was responsible for almost 600,000 deaths in 2013. Children in Africa account for most of the fatalities, and the WHO estimates that currently one African child dies from malaria every minute of every day.[4] Those who have su ered through malaria multiple times as adults will attest that malaria, with the exception of its most virulent strains like plasmodium falciparum, is usually more of a nuisance than an emergency for healthy adults. It causes symptoms like headaches, fever, and chills. Even though it does not usually constitute a medical emergency for adults, malaria does decrease productivity and has significant treatment costs. On the other hand, yellow fever has a high mortality rate—about 50%—even amongst healthy adult populations.[5] While malaria and yellow fever have historically taken the largest toll on human populations, one of the main effects of trypanosomiasis (or sleeping sickness) has been to limit the practicality of keeping certain types of livestock in Africa. Horses and many breeds of cattle are especially susceptible to trypranosomiasis, which is spread by the tsetse fly and can lead to either chronic illness, characterized by weight loss, fever, anemia, cardiac lesions, and other symptoms in animals, or to a more immediate death. Until the past fifty years or so, in many parts of the continent, these noteworthy challenges with disease, alongside the low fertility of the soils and the unpredictable rainfalls, were significant constraints on human pop-ulation growth. Environmental challenges and disease also affected settlement patterns as, for example, people avoided more forested and wetter areas because of the prevalence of mosquitoes. Additionally, Africans continuously adapted their herding and farming techniques to overcome these challenges.
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