High blood pressure of unknown cause (essential hypertension) is the major chronic illness contributing to premature morbidity and mortality in Western Hemisphere Blacks. As a group, Blacks in the Western hemisphere have higher mean blood pressure levels than Blacks from Sub-Sahara Africa where essential hypertension is strikingly less common. Because of the similiar heritage of these populations it has been suggested that blood pressure differences between them is most likely due to environmental differences between them is most likely due to environmental differences such as variations in diet or behavioral stress.

We suggest a new hypothesis:

selective survival related to sodium (Na+) metabolism during the slavery period of Western hemisphere history has led to inherited genetic differences between Western hemisphere Blacks and Sub-Sahara African Blacks which now play a major role in these geographic variations in blood pressure. Most Blacks in the Western hemisphere are descendants from a population of sub-Saharan Africans that survived the select pressure of the trans-Atlantic slave trade and New World slavery; ancestors of most current Black Africans had no such experience. The present article reviews the importance of Na+ metabolism in the causes of mortality during the slave trade and estimates Na+ losses due to sweating, diarrhea and vomitting. The magnitude of these potential losses make it likely that fatal Na+ depletion was a major contributor to the high mortality. Thus, we suggest that slave trade imposed severe demands on Na+ homeostasis and those most likely to survive were more capable of conserving Na+ than those who did not. In today's high dietary Na+ environment the descendents of African slaves may be more susceptible to "Na+ sensitive" hypertension than the descendents of Black Africans without this heritage