4. cause a steady decline in average intelligence of the community. This consequence is inevitable just in so far as intelligence is inherited. The assumption is that the genetic factors which produce mental ability of a high standard will become rarer and those which tend to produce mental ability of low standard will become commoner. The present rate of decline due to genetic changes has been estimated by Cattell[superior 15] to be of the order of one point in the intelligence quotient (or one per cent.) every ten years: it is clear that such a precipitate fall in general intelligence would soon produce a [strikeout] population of simpletons. The process cannot have been going on in this way for long because, if so, a century or two ago we must have been a nation of geniuses. [Add insert: see image 2232] In my view, the arguments used to prove [strikeout text] that such a precipitate decline is likely are fallacious because the birth rate is highest among people whose average intelligence quotient is from 90 to 95.[superior 16] If conditions continue as they are at present, the end result of the differential fertility would be to produce a population with an average intelligence quotient scarcely below that which now exists in rural districts. This point, however, would be reached slowly. The prospect of even a slightly abnormal community is not very encouraging to those interested in mental hygiene, particularly when we remember that there is an association between delinquency and mental retardation. Moreover, no educationalist can view with equanimity the prospect of having to provide for more and more dull pupils and fewer and fewer children of scholarship standard, even if the change in number is slow. It is possible that indirect estimates based on differential fertility may be in some unforeseen way erroneous. [Note to insert 2 here] The direct method of checking whether an intellectual decline is taking place would be to examine very large representative groups of children at regular intervals, say of 5 to 10 years, with the same standardized mental tests. Unless the standards are kept constant, evaluation of the results of periodic surveys may be extremely difficult. The incidence of mental defect in England and Wales was estimated by Lewis in 1929 to be double the incidence estimated by Tredgold in 1904[superior 18]. It is impossible to assess how far this difference between the results of the two surveys was due to a real increase and how far it is an artefact because different methods of investigation and testing were used by the two observers. Mental deficiency will apparently become more prevalent in any district where mental health services are developing because of improvement in facilities for ascertainment. Direct proof of the lowering of average intelligence in this country is lacking, but there is a large amount of indirect evidence which points to a genetic position which is unfavourable from the point of view of national intelligence in the future. Moreover, if, in addition to this, the general decline in birth rate continues, [Note here to insert text Insert 3] the types of idiocy of which maternal age or primogeniture is a part cause will become more frequent. The facts of population on which a decline in average intelligence can be predicted are not peculiar to the British Isles: indications of similar trends can be found in statistics of almost all civilized countries[superior 21]. The quantitative aspect of a declining birth rate, hoever, is more often stressed than the qualitative aspect, but it is the qualitative aspect in which we should expect the educationalist to be specially interested. It is hardly within the terns of reference of my part in this discussion to suggest remedies for the present state of affairs, but it is evident to me that a civilized community which is able [end]