What are the Effects of population on human health?

This question is worthy of a thesis; not a quick one-liner here. That said, I'll indulge in a huge amount of generalization: Humans are a social animal -- we don't exist well alone, and so we form up into small groups in the wild. In prehistoric times, evidence indicates that nomadic groups were typically numbered between 50 or 100 persons at any given time. And so the minimum base population was one in which any given group, in order to survive and propagate, and in order to maintain genetic diversity, would need to meet other, genetically non-identical groups. Factors invovled would of course include the availability of food and water, climatic causes for the necessity of shelter (versus travel), the possible presence of geographic features that increased likelihood of encounter, etc. This then is the low end of the population bell curve as it relates to long term survival. As population density increases, more and more interaction between genetically diverse groups occurs. This causes a wider, healthier genetic base to form up and, semiotically, allows for a faster and more inclusive mimetic diversity as well. So we see an increase in survivability in physiological, nutritional, sociological and semiotic areas. After a time, and as with any organism, over-crowding sets in and starts to generate a complex of health-related factors. In mammalian populations, when nutrition is not a factor (e.g. there is ample food and water available, and sewage is also not a problem), gross overcrowding showed at first an increase in cardiovascular events as well as an increase in psychological presentations that could be related to neuro-physiological phenomena. An experiment circa the 1960's with Sikh Deer on an island that presented more than amble pasturage and no sewage related health issues, showed an annual increase in the population until density was approximately 400% over max norm. The next year's study showed a massive population die-off, in which the living population had reduced to roughly 90% max norm. Autopsies of recently dead individuals showed adequate nutrition, but also the effects of a high degree of stress (indications of intense, chronic cardiovascular strain) as well as a high level of adrenochrome, a metabolite of adrenalin. The interpretation was that the animals, who experienced a fight-flight reaction on over-close proximity with other animals, hyper-secreted adrenalin, and suffered for it. What caused the sudden die-off at exactly that point was not determined in the course of this study and, in most naturally occurring cases, this level of population density will not be reached, as groups will migrate away, if they can. We can therefore surmise that, after the maximum beneficial population density is reached, we will see a decline in the overall health picture, as population increases. Cardiovascular problems and other stress-related pathologies start to manifest in greater and greater incidences, as well as stress-related psychopathologies. We also note that intense chronic stress can result in a loss of efficiency of the immune system, thus paving the way for unusual mini-epidemics and epizootics. In summary, starting at minimum population density, health increases to an optimum level, and then falls off as population surpasses the max safe density.