For this purpose we augment the 100 families of the preceding section by the addition of 240 more families like them, and we examine each family history to find how many of the children died before completing the fourth year of life. The data are summarized in the following table:
Child Mortality in Families of Long-lived Stock, Genealogical Record Office Data
| Size of family | No. of families investigated under 5 years | No. of families showing deaths | Total no. of deaths | |
|---|---|---|---|---|
| 1 | child | 6 | 0 | 0 |
| 2 | children | 6 | 0 | 0 |
| 3 | " | 38 | 4 | 5 |
| 4 | " | 40 | 6 | 7 |
| 5 | " | 38 | 4 | 4 |
| 6 | " | 44 | 12 | 13 |
| 7 | " | 34 | 8 | 11 |
| 8 | " | 46 | 13 | 18 |
| 9 | " | 31 | 14 | 20 |
| 10 | " | 27 | 14 | 14 |
| 11 | " | 13 | 6 | 9 |
| 12 | " | 13 | 9 | 16 |
| 13 | " | 1 | 0 | 0 |
| 14 | " | 2 | 0 | 0 |
| 17 | " | 1 | 1 | 2 |
| — | — | — | ||
| 340 | 91 | 119 | ||
The addition of the new families (which were not subjected to any different selection than the first 100) has brought down the child mortality rate. For the first 100, it was found to be 7.5%. If in the above table the number of child deaths, 119, be divided by the total number of children represented, 2,259, the child mortality rate for this population is found to be 5.27%, or 53 per thousand.
The smallness of this figure may be seen by comparison with the statistics of the registration area, U. S. Census of 1880, when the child mortality (0-4 years) was 400 per thousand, as calculated by Alexander Graham Bell. A mortality of 53 for the first four years of life is smaller than any district known in the United States, even to-day, can show for the first year of life alone. If any city could bring the deaths of babies during their first twelve months down to 53 per 1,000, it would think it had achieved the impossible; but here is a population in which 53 per 1,000 covers the deaths, not only of the fatal first 12 months, but of the following three years in addition.
Now this population with an unprecedentedly low rate of child mortality is not one which had had the benefit of any Baby Saving Campaign, nor even the knowledge of modern science. Its mothers were mostly poor, many of them ignorant; they lived frequently under conditions of hardship; they were peasants and pioneers. Their babies grew up without doctors, without pasteurized milk, without ice, without many sanitary precautions, usually on rough food. But they had one advantage which no amount of applied science can give after birth—namely, good heredity. They had inherited exceptionally good constitutions.
It is not by accident that inherited longevity in a family is associated with low mortality of its children. The connection between the two facts was first discovered by Mary Beeton and Karl Pearson in their pioneer work on the inheritance of duration of life. They found that high infant mortality was associated with early death of parents, while the offspring of long-lived parents showed few deaths in childhood. The correlation of the two facts was quite regular, as will be evident from a glance at the following tables prepared by A. Plœtz:
Length of Life of Mothers and Child-mortality of Their Daughters. English Quaker Families, Data of Beeton and Pearson, Arranged by Plœtz
| Year of life in which mothers died | At all ages | |||||
|---|---|---|---|---|---|---|
| 0-38 | 39-53 | 54-68 | 69-83 | 84-up | ||
| No. of daughters | 234 | 304 | 305 | 666 | 247 | 1846 |
| No. of them who died in first 5 years | 122 | 114 | 118 | 131 | 26 | 511 |
| Per cent. of daughters who died | 52.1 | 37.5 | 29.9 | 19.7 | 10.5 | 27.7 |