Life of Francis Galton by Karl Pearson Vol 2 : image 149

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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		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.