Salt is one of the most ancient things of value to man, as a moment’s reflection on the origins of words – like salary (something worth working for) quickly brings to mind. Roman soldiers were paid in salt, not silver. By the 1950s, a pound of sodium chloride was one of the best bargains around, available in most supermarkets for approximately 13 cents. It was about this time that Dr. Lewis K. Dahl noticed that in populations of Sprague Dawley lab rats, there existed a sub-group of salt sensitive individuals that developed hypertension spontaneously when fed a high salt diet. With just three generations of brother-sister matings, Dahl was able to segregate the salt intolerant trait into Dahl S (for salt sensitive) animals. He also raised its counterpart, the Dahl R (for salt resistant) rat. Dahl S rats fed a diet 1% by weight sodium chloride rapidly developed sustained hypertension and died by four months of age; tellingly Dahl R rats on the same diet did not. The medical community of hypertension specialists at this time were essentially a bunch of plumbers. They were not informed by evolutionary paleoanthropology. Using crude loop diuretics like furosemide (lasix) they learned to treat high blood pressure by opening a tap in the kidney and pouring salt and water out in the urine. Ignoring the vast differences between a small furry rodent and a naked, heat-adapted endurance predator, they assumed that the Dahl S rat was a viable model of human hypertension.
The resulting emphasis on dietary salt restriction in both research and public health policy during the last 60 years cannot be exaggerated. It cannot actually be read (in any feasible amount of time) – it amounts to tens of thousands of papers, editorials and educational campaigns – it pervades and saturates. And for want of a simple Paleolithic perspective, all those trillions of dollars generated mostly hubris. A typical sample of that is the 2005 review by Meneton et al in Physiology Reviews. This paper references 414 others. By totaling the costs of less than ten of the larger of these studies one quickly surpasses $1 billion in ill-advised public spending. It states without evidence that the pre-modern human diet was the same as a chimpanzee. The author also states, relying only on modern anthropological anecdotes, that the adapted state of the human species is to ingest less than 1 gram of salt per day, an amount that modern man can eliminate by perspiration in 20 minutes. The words “perspiration” and “sweat” do not appear in this review one single time. That’s a pretty big oversight. This is because with respect to salt and water, human beings are a uniquely strange animal. We have at least two million and perhaps 40 million eccrine sweat glands, capable of pouring out 3 liters of isotonic fluid and 2.8 grams of sodium chloride per hour.
We have in essence 3 kidneys – a widely dispersed and inefficient one all over the surface of our bodies, and two additional, highly refined internal ones to clean up whatever imbalances perspiration leaves us. (There are only 800,000 to one million nephrons per kidney, so sweat glands probably outnumber them, but a nephron is a sophisticated work of bio-engineering if ever there was one. The nephrons move 800 grams – more than a pound – of pure salt into your nascent urine every day, then recycle >99.99% of that back to your blood, leaving as waste between 50 mg and 50 grams, customized to your diet and the sort of day you had.)
The sort of day humans evolved to have is that of a cunning persistence predator with no advantages of speed or weaponry. This is our African, heat adapted inheritance, which can be summarized like a panhandler’s cardboard sign: “Will run marathons for food.” We have an evolutionary bet with large ungulates that we can harass them in the open sun until they overheat and die before we do. By eating liberally of their salty tissues and drinking copiously of free water, we recharge ourselves in order to take down another of their brethren in a few days time. The physical signature of that strategy perfected over millennia is stamped onto our genes and our bodies. Humans have sported a highly derived, spring-loaded ankle and foot for more than 2 million years. We have evolved to handle sodium and water like no other animal – and certainly not in the manner of a Dahl S rat. We re-purposed the excess salts from our new diet to create profuse perspiration. We altered the physiologic essentials of blood volume and water balance. We lost our body hair, and developed arterial shunts to our surface veins, turning the dorsal hands and forearms into heat radiators. We grew a wet mop of hair on our head. It’s a lifestyle with little appeal to vegans, but the early hominids that embraced chewing roots instead left us only their enormous molars and crested skulls as fossils emblematic of an adaptive error. They’re extinct now.
Until last month, the most ancient whole genome ever sequenced from the DNA residues extracted from fossilized bone was from a polar bear. Continuously frozen in ice for about 120,000 years on Svalbard Island, Norway, this 
Kirk M. Maxey: Blog and Website 