In the ensuing section the focus shifts via the slave trade from Africa to the West Indies and the southern United States, while it continues to remain riveted on black resistance to yellow fever and malaria.

As mentioned previously, medical science has not acknowledged that blacks were gifted with innate yellow fever protection relative to whites. Yet that resistance is discernible in the vast epidemiologic laboratory of history, which Chapter II explores. It is not, however, always clearly discernible, because acquired immunity to yellow fever sometimes camouflages innate protection. Therefore special (perhaps even excessive) care has been taken in disentangling the two, so that the statistical evidence upon which much of the chapter rests, evidence generated in abundance by yellow fever's repeated assaults on cities of the West Indies and the American South leaves no doubt of the blacks' superior ability to host the disease and survive.

By contrast much of the reason why blacks have historically proved resistant to malaria is known to medicine; yet, perhaps paradoxically, it is much more difficult to spy this resistance at work than to detect blacks' resistance to yellow fever.

Yellow fever's appearances were specific and limited epidemic events, which means that differential morbidity and mortality by race are easily linked to those appearances. But malaria fevers worked constantly, year in and year out, quietly killing not only directly, but indirectly as well, by weakening the victim, leaving him susceptible to the fatal effects of intercurrent diseases.