Fig. 2

Illustration of the hypotheses of evolution and natural selection on the impact of blood pressure variability of the ancestors of anatomical modern human (AMH). During the Pleistocene Period, the ancient AMH practiced hunting-gathering lifestyle thus required higher physical stamina and endurance. Consequently an effective system of O₂ exchange was evolved in such a way that smaller size of red blood cells, capillary diameters but denser capillarization to cater increasing sustained aerobic activity. As compensation to the physiological adaptation, systemic BP is elevated to suffice blood flow in the circulation. The savannah climate was hot and humid resulting in excessive sweat loss thus unavoidable sodium loss. The scarcity of salt further stringent deficiency. Kidney would then adapt an effective sodium and water retention which in turn elevated the renin-angiotensin-aldosterone system (RAAS) hence increase in blood pressure. Chronic infections with pathogens, notably the plasmodium sp. infection promotes disruption of RBC and effects on endothelial cells, subsequently triggered oxidative stress to the circulation, thus enhancing the renin-angiotensin-aldosterone system (RAAS) which in turn elevated BP. Low energy intake yet high requirement of physical stamina and endurance of the savannah hunters and gatherers often resulted in starvation. Prolonged starvation led to reduction of BP thus resulted in increased arterial tone and force of cardiac contraction to maintain BP and ensure organ perfusion. Therefore, genetic variation that enhances arterial and cardiac contractility, as well as those of energy-preservation preference was of selective advantage. In addition, foetus in the mother with low energy intake would alter the energy metabolism pathways to cope with famine. Postnatally in a nutrient rich environment, the altered physiological changes became maladaptive therefore increased risk of elevated BP. Out-of-Africa, natural selection and genetic drift may have resulted in lower ancestral allele frequencies of genes responsible for salt homeostasis in AMH habitation at higher latitude. Whilst during ‘middle passage’ and enslavement, a sudden drop of number of enslave caused a severe bottleneck. Those that survived however, are likely to carry excess frequencies of the ancestral alleles that allowed rapid adaptation to the extreme stress of dehydration. AMH carrying the ancestral alleles in modern lifestyle with resource enriched environment thus became maladaptive against the snail-speed evolution therefore increase risk of hypertension