Diseases

When modern humans began to move out of Africa to Asia and beyond one hundred thousand years ago, the number of Homo sapiens sapiens was probably no more than a million, most of whom lived in Africa. They were hunters and gatherers in small family groups who foraged for food in a radius not more than one day's walk from water. There was ample room to roam, 6 million square miles through grass and woodlands, which bipedal modern humans did with increasing vigor. The family clans and groups were consequently widely distributed and few in number compared to the continental landmass. Today Africa has a higher birthrate than any other continent, but this is a phenomenon of the past century. Previously, the rate of population growth in Africa has been consistently lower than that in more temperate climates. Although many explanations have been put forward, the most likely is the inability of the environment to sustain an increase in the population of Africa. When the capacity of the land was limited, the number of Africans remained relatively constant. When the climate, land, and inhabitants produced food in abundance, their numbers rapidly expanded, and as mobility of those with tools and fire increased, they migrated into the more productive regions of the continent. One would expect the increased birth rate, made possible by the increase in food production, to result in a concomitant increase in the total population of Africa, but this did not happen. To be sure, the numbers of Africans steadily but gradually expanded, but those who survived were far fewer than those who roamed and then settled in Asia, Europe, and ultimately in North and South America. They had all come from the same evolutionary beginnings, but the enormous disparity in terms of population growth between those who had moved out of Africa and those who remained can best be explained by the tropical diseases that debilitated the Africans.