proof, that the death rate among these two classes, the Irish and the negroes, is much higher than that of the general population. I have not at hand statistics which will conclusively prove this fact, and will only quote the tables prepared by General Walker, based upon the United States census of 1870, in which he shows that while the Irish constituted three hundred and thirty-three per thousand of the foreign population, they contributed four hundred and ten to every thousand foreign-born decedents, thereby largely exceeding their due proportion.
If we accept the opinion alluded to as a fact, we are brought face to face with the paradoxical condition of a large proportion of persons reaching extreme longevity among classes noted for a low average longevity. How to account for this apparent anomaly is a question of interest. But one explanation suggests itself to me, and this I believe to be, in the main, the true one—namely, that the centennarians of the classes named owe their great age to favorable heredity, a natural life-force and power of endurance transmitted to them by their ancestors, which enabled them to withstand or overcome the unfavorable environment which carried off a large proportion of their respective races; while, on the other hand, the admittedly higher average longevity of the native whites is to be accounted for by their more favorable surroundings and mode of life, better hygiene in health and care when sick, whereby the vitality of the weak, the sickly, and the young is conserved, and many years of life are added to the average. If this explanation be accepted as the correct one, it suggests the law, which is also warranted by a wider observation, that extreme individual longevity depends chiefly upon favorable heredity, while a high average longevity is promoted mainly by a favorable environment.