Normal, i.e., average.
Advanced, i.e., above average.
| Retarded. | Normal. | Advanced. | |
| A Manual workers B | 45.2 36.7 | 47.1 55.9 | 7.7 7.4 |
| C Artisans, etc. D | 29.4 28.8 | 50.2 50.2 | 20.7 19.5 |
| E Most comfortable | 12.7 | 62.7 | 24.6[[A]] |
[A] I am indebted to Professor McDougall's book for information here given.
These experiments all shew the trend of intelligence (and with it will power or power of concentration, and what we may call general capacity) to be more concentrated in the so-called higher grades of society, and to be less and less evident as we descend in the scale from skilled to unskilled workers. It would, of course, be clear to all that the children of mentally deficient parents can only be a burden on the State or can rarely contribute anything of value to the common weal.
Now the teaching and advocacy of methods of conception control is most easily assimilated and practised by the intelligent classes; indeed, we may say with certainty that such methods can only be used effectively by the intelligent members of the community, such as leisured, professional and mercantile classes, skilled artisans and better class workers, whereas the lowest type of casual labourers whose home conditions render the use of preventive methods difficult or impossible, and the mentally deficient and criminal classes, are unaffected by such teaching.
The result in a few generations must be a marked decrease in the numbers of the intellectual and efficient workers, while the hopelessly unfit continue to produce their kind at the same rate as before.
The figures given do not suggest that individuals with marked ability are to be found in the upper classes only, but they do indicate that there is a larger proportion of boys and girls in the more comfortable classes whose inherited ability is above the average, though this may be partly due to the more intellectual atmosphere in which their early childhood has been passed.
The provision of education for all, with facilities for children of every class to pass on to higher grades of work, is essential if the latent powers in all, whatever they may be, are to be developed to the utmost.