124
Life and Letters of Francis Galton
populations to a standard population (the average of the two) of wives. The following resulted
Mother's age |
Number of wives |
Number of Average number children of children per wife |
Standard Population |
Standard popu lation. Total children | |||||
Factory |
Rural |
Factory |
Rural Factory I |
Rural | |||||
Factory |
Rural | ||||||||
24 and 25 |
107 |
91 |
137 |
130 1.28 |
1.43 |
99 |
127 |
142 | |
26 and 27 |
122 |
104 |
209 |
190 |
1.71 |
1.83 |
113 |
193 |
207 |
28 and 29 |
132 |
119 |
304 |
279 |
2.30 |
2 34 |
125.5 |
289 |
294 |
30 and 31 |
120 |
119 |
299 |
368 |
2.49 |
3.09 |
119.5 |
298 |
369 |
32 and 33 |
128 |
124 |
371 |
403 |
2.90 |
3.25 |
126 |
365 |
410 |
34 and 35 |
132 |
120 |
430 |
401 |
3.26 |
3.34 |
126 |
411 |
421 |
36 and 37 |
100 |
117 |
369 |
395 |
3.69 |
3.38 |
1085 |
400 |
367 |
38 and 39 |
100 |
128 |
354 |
469 |
3.54 |
3.66 |
114 |
404 |
417 |
40 |
59 |
78 |
208 |
276 |
3.52 |
3.54 |
68.5 |
241 |
242 |
Totals |
1000 |
1000 |
2681 |
2911 |
2.68 |
2.91 |
1000 |
2728 |
2869 |
From this table w e see that Galton overlooked the fact that his Coventry sample consisted of younger women than his rural Warwickshire mothers, and therefore would naturally have fewer children. The average difference on the standard population is only .14 of a child, or if we take the average interval between births to be 2.5 years, it follows that a postponement of marriage on the average for four months would explain this difference'. Thus far Galton's paper would not justify any statement as to deterioration arising from town-life. The lesser apparent fertility would be fully accounted for by emigration of the younger women into the towns and a slight postponement of marriage. Galton next proceeds to take the influence of mortality on the town and rural populations. Failing other data he applies to Coventry the mortality table of Manchester and to the rural districts of Warwickshire that of the `Healthy Districts.' I do not think either of these steps is justifiable, nor again the method by which he applies these life-tables. He draws the conclusion that
"the rate of supply in towns to the next adult generation is only 77 per cent., or say, threequarters of that in the country. In two generations the proportion falls to 59 per cent., that is the adult grandchildren of artisan townsfolk are little more than half as numerous as those of labouring people who live in healthy country districts." (p. 23.)
This conclusion has been often cited as if it were rigorous, whereas it is rather an illustration of the grave difficulty of inquiries of this nature, even
i This suggestion is supported by the fact that as the women get older there is a less difference between their number of children, e.g. Mothers 36-40, Factory 3.59 and Rural 3.52, or the town is in excess.