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Population Density and Disease
Population Density and Disease

Population Density and Disease

In “Infectious Diseases and Human Population History: Throughout history the establishment of disease has been a side effect of the growth of civilization” (BioScience Vol. 46 No. 2, Feb 1996), Andrew P. Dobson and E. Robin Carper write:

Archeological studies on human communities entering the transition between hunter-gathering and primitive pastoralism provide evidence suggesting that a more sedentary existence tended to lead to increased child mortality and high levels of disease. A significant characteristic of this malnutrition was a reduced diversity in diet as humans switched from a mixture of meat, grains, and fruit to a diet dominated by grains.

Hippocrates (460-377 B.c.) was probably the first person to record diseases with enough precision for them to be identified today as malaria, mumps, diphtheria, tuberculosis, and perhaps influenza. The Greeks were definitely aware of palmonary tuberculosis-an epidemic of tuberculosis seems to have raged during Hippocrates’ lifetime. Hippo-crates also described many other recognizable infections, including malaria, so it is apparent that these diseases were present in Hellenic times. Interestingly, none of Hippocrates’s records indicate the presence of smallpox, measles, or bubonic plague in ancient Greece, which suggests that the size of ancient Greek and Egyptian cities may not have been large enough to continuously sustain measles and smallpox infections, and these pathogens may have died out.

It is likely that many of the plagues mentioned in the Old Testament arose when human populations became sufficiently aggregated to sustain epidemics of new pathogens. Because human populations had not previously been exposed to pathogens such as smallpox, rubella, measles, levels of immunological resistance were low and mortality rates were high. After several visitations by a specific pathogen, levels of genetic resistance and herd immunity start to increase, leading to reduced pathogenicity and a more regular pattern of prevalence.

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