One of the salient points made by Jared Diamond in his (sometimes reviled) Guns, Germs, and Steel is that humans living in close proximity to livestock will develop, over generations, better immunity to the diseases this practice encourages. In contrast, when more nomadic and less agriculturally inclined populations are subsequently exposed to those same diseases they have catastrophically low immunity.
This got me thinking. If the two lifestyles create such different levels of immunity, it suggests that transitioning from hunter-gatherers to more advanced societies must have radically changed the landscape of human disease.
What did early humans deal with in terms of diseases? Did they have fewer diseases to contend with, perhaps as a result of a much lower population density? How long has malaria been around for in humans, for example? Did disease go up dramatically as a cause of death when societies started to domesticate? Did the number of human diseases continue to rise until the advent of medicine, or was there an initial spike at domestication and then plateauing, or even a decrease in number as the more successful diseases adapted and thrived?
I realise this is a very broad question, and I don't ask for too much detail, but I can't help but feel that it's a hugely important topic that I know almost nothing about. Any info people can provide would be greatly appreciated.
These questions are more suited to one of the anthropology or evolutionary biology subreddits, but I’ll attempt a brief answer.
The patterns of human disease have indeed changed since people settled down. Some of the more important reasons include:
Going over these one at a time, increased population density has several effects. First, it leads to a rise in infectious diseases because individuals are in close contact with a larger number of other people, and can therefore transmit such diseases to more people. Probably the first epidemics arose in this period. Second, when humans settle down and congregate, they produce a lot of human waste, which requires advanced sanitation technology to safely dispose. This took a while to develop, and meanwhile, diseases transmitted by human waste (cholera, typhoid, etc.) became much more prevalent. The use of human feces as fertilizer transmits various intestinal infections to people who eat plants grown in such conditions. Third, there is a transformation of the landscape, for example, agriculture produces pools of stagnant water, in which many insect vectors can multiply, including mosquitoes which transmit malaria, yellow fever, dengue, or liver flukes or schistosomiasis. Agricultural practices such as turning over the soil exposes people to insect bites and diseases such as scrub typhus. Many of the “community diseases” such as influenza, measles, mumps, smallpox – either first appeared, or became much much more prevalent in these early settlements.
The domestication of animals led to close contact with these animals, which increased the spread of zoonotic diseases caused by parasites that can use humans for part of their life cycles. Animals products from these domesticated animals, including meat, milk or hides and wool also spread such diseases. Anthrax, brucellosis, tuberculosis are some of these diseases. Zoonotic diseases spread by insects also became a problem, such as trypanosomiasis, filariasis.
The agricultural revolution had a profound effect on human diet, and initially, the impact was pretty bad. Variety in the diet decreased as humans became more dependent on a few staple crops, and diseases of malnutrition and deficiencies increased. Stored agricultural products were prone to food poisoning by various fungi, and they attracted pests such as rodents, which also transmitted diseases. There were probably other far reaching effects of agriculture on things such as fertility, weaning practices, child labor, which also had effects on health and disease, but that’s a whole other discussion in itself.
As humans were exposed to new diseases, some degree of herd immunity developed. Nomads who came into contact with settled people had no such immunities, which caused much devastation when settled and nomadic populations intermixed.
Moving to individual diseases, you asked about malaria. This is a very old disease, going back long before there were humans. Anopheles mosquitoes with plasmodium in their salivary glands have been found trapped in amber going back to the Miocene, 20 million years ago. Malaria-like diseases occur in a vast range of animals, from rodents on through all primates, including humans. These diseases followed us right down the evolutionary tree. Other diseases of our nomadic ancestors included head and body lice, pinworms, lots of bacterial infections such as salmonella, typhus, staphylococcus, tetanus, various kinds of food poisoning. Zoonotic diseases were a constant threat, including sleeping sickness, relapsing fever, leptospirosis, trichinosis, tularemia, avian/ichthyic tuberculosis. These are all diseases found in contemporary hunter/gatherers as well, depending on the climate they live in.
Of course, the effects of settled life and agriculture don’t just end there, they are ongoing. Since you were interested in the transition between nomadic and settled life, that’s what I talked about. But you could go move ahead a few thousand years and on to the urban revolution, and all the new diseases and problems (and their solutions) that arose. Or move on to the industrial revolution and the massive increase in food supplies and increase in lifespans, and talk about the rise of chronic and degenerative diseases. Or to present times, and talk about antibiotic resistance and the resurgence of infectious diseases. Change just keeps happening.
I can't answer your question, but maybe one of the anthropology subs might get you some answers. Hell, I think they might even have to direct you to a sub dealing with evolutionary biology.
I'm not aware on the particulars further back in history but a very recent pattern has arisen that suggests that countries with advanced health care and thus low infection rates tend to suffer from markedly increased rates of autoimmune conditions, such as lupus, and allergic/atopic conditions such as asthma.