I
suspect that, as a rule, the answer is none. Before man started living in cramped, unhealthy conditions in ghettos, working in sweathouses or swamps, using the waterways as sewers, spraying poisons on fruit and vegetation, obtaining drinking water from lead pipes, breathing factory and vehicle emissions and any of the countless other methods that we've devised to ruin our health, disease would have been a little known experience.
Sure, there would have been bad times such as the supervolcano eruption in Asia about
70,000 years ago when just about all above ground vegetation was killed off. Homo sapiens would have had to survive on whatever could be found while wandering across vast deserts searching for potable water. Anyone who made the mistake of drinking or eating anything contaminated by the poisonous ash would likely have exhibited many of the symptoms that we associate with disease today and died due to the inability to reach sustenance.
Check out the demise of the Fuegians as discovered by Darwin and Fitzroy. In perfect health when found but in short order on the journey back to England, 4 had been vaccinated for
smallpox and one died of smallpox shortly after that. (A 75% success rate - very good.)
Not to worry though because before long, the white man's diseases, greed and alcohol had brought the population to extinction.
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Sorry but I was not suggesting that our species "merely" survived. It is
more likely that they thrived as they would have been living in the "garden of Eden" so to speak with fresh fruit and vegetation available year round. We know of one natural disaster where they would have been "thrown out of the garden" and many would have had to learn to live on less choice fare just to survive.
The move from hunter/gatherer to farmer saw another downturn in health:
Biological Changes in Human Populations with Agriculture
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And I'm certainly NOT suggesting eugenics. Heck, I can barely spell the word. Perfect health is the birthright of every living creature and each organism strives for ultimate health. With a species correct diet of wholesome, natural foods as well as a clean and pleasant environment, all of us will achieve our ultimate health. Unfortunately, generations of poor diets, less than optimal environments and the outrageous treatment of patients (especially women) by the medical and other industries have robbed many of us of our highest potential.
The less-resilient of humans will succumb quicker to a toxic environment and lifestyle than those with higher vitality. The answer to keeping them alive and healthy is not injecting them with foreign matter cultured on chicken eggs or monkeys although I've heard that hanging a dead crow by their front door is mighty effective.