When the Committee on the Regional Plan of New York four or five years ago began its study to determine how residential areas should be developed in the New York Region, it was confronted with a lack of standards of density and of use - not merely for residences, but for other structures that come in close proximity to residences. An attempt was made, therefore, to analyze the factors held by the courts to justify the employment of the police power in zoning. Our courts hold that the police power, as is well known, can be employed only to promote and protect health, safety, morals and the general welfare.
The first thing we did was to analyze the problem of density of occupancy - and, in particular, residential occupancy - with regard for these four factors.
The New York City Health Department figures showed some interesting contradictions. The sickness rate per thousand from such diseases as measles, mumps, chicken pox, diphtheria, scarlet fever, etc., was much less in the areas where the density was 200,000 persons per square mile than in districts where the density was much lower. Not only that, but the number of fatalities arising from motor vehicle accidents was much less proportionately in the congested areas. The pneumonia and tuberculosis rates showed similar divergencies. A closer study revealed that the East Side youngsters not only do not get hit so often by motor trucks, but, when they do get hit, do not die, to the same extent as others.
This prompted us to make further inquiry of the Health Department to ascertain the reason for this phenomenon. It appears that inherited resistance to disease, inherited stamina, and inherited vitality resulting from a long process of survival of the strongest under bad conditions in older civilizations have built up a high resistance, or immunity, in the people who have occupied the districts affected. Therefore, in any study of city-wide rates, there must be taken into consideration those factors of racial resistance that are found in certain districts.