Based on data obtained from the marriage registers of seven Oxfordshire parishes in the Otmoor region, an analysis has been made of the effects of social mobility and marriage exchanges on the relatedness of the five social classes which are recognized by the Registrar General. From a starting position in which it is assumed that there was no relatedness between the classes, it is calculated that under the average social mobility patterns which have characterized the area from 1837 to 1967 the different social classes would come to share 95% of their ancestry in sixteen generations. The marriage movement would produce the same levels of relatedness in twenty generations, and the combined effects of social mobility and marriage produce homogeneity in nine generations. It is further argued that these are maximal estimates but in considering the genetic implications it is noted that, whilst genes which do not affect social mobility and marriage movement are not likely to show social stratification in Otomoor populations, genes affecting behavioural traits may well be heterogeneously distributed.

Sex in man and probably throughout the class mammalia is normally determined by the presence of a Y chromosome (male) or its absence (female). The presence of genetic loci on both the long and the short arm of the X chromosome in double dose appears to be essential for the development of mature functional ovaries in the human female though a single X suffices in the female mouse.

The development of masculine genital anatomy and phenotype is a consequence of prior formation of testes. In the absence of gonads of either kind, female internal and external genitalia are formed but secondary sex development fails. In rare human families a mutant gene suppresses the development of male external genitalia in 46, XY embryos but permits the development of testes and male internal genitalia. The external phenotype is normal female (syndrome of testicular feminization). A sex-linked mutant gene in the mouse has a similar effect.

The locus or loci directly concerned with male development might lie wholly on the Y chromosome or might be located on another chromosome or chromosomes. In the latter case it (or they) must be repressed in the female and normally activated by a locus or loci on the Y chromosome in the male. Present evidence does not permit the exclusion of either possibility.

Data concerning occasions of coitus were recorded by 241 married couples who had sought advice from the Catholic Marriage Advisory Council about the basal body temperature method of regulating births. The present analysis deals with the 6 days of the post-ovulatory phase which are considered to be least affected by intended birth regulation. The distribution among couples of coital frequencies is tabulated by age of wife; the mean frequency during the 6 days is 1·8 (Table 2) but this value may be influenced by the fact that some couples had avoided coitus in the pre-ovulatory phase. The hypothesis is examined that the probability of coitus on any day is unaffected by whether or not coitus occurred on the previous day. Sufficient data are available to show, as expected, that not all couples behave in the way described by this hypothesis. It is estimated that for about a third of the couples the probability of coitus is decreased if it occurred on the previous day (alternators). There are also significant numbers for whom it is increased (persisters), besides those conforming to the hypothesis.

In this paper an attempt is made to indicate how the number of coloured people in England and Wales might be expected to grow in the future. The best available estimate of the initial distribution by sex and age of the coloured population would appear to be that prepared by the Institute of Race Relations and this has been used by the author. Suitable assumptions are made regarding the fertility of the immigrants and possible rates of immigration. The calculations are illustrative, with the objective of providing a framework within which a discussion of the growth of the coloured immigrant community of Britain can proceed. The results obtained are summarized in Table 3.

The incidence of spina bifida and anencephaly, according to reports, has declined in some parts of the world but not in others. It is suggested that social factors, greater awareness of the familial nature of these disorders coupled with the increased availability of effective contraception, may account for part of the decline and that these factors are less operative in the areas where no decline in incidence has been observed.

Data are presented for 65 families living in the Manchester area, each of which contained at least one affected child. Forty of these families appeared to have been ‘discontinued’ after the birth of the affected child.

The physical changes which take place at puberty in both sexes may be classified under the following headings:

(1) Morphological. The rate of growth increases but this acceleration is greater in some dimensions than others so that the overall shape of the body changes, i.e. the rate of change in both size and shape alters.

(2) Body composition. There are changes in the relative amounts of bone, muscle and fat.

(3) Physiological. There are changes, particularly in the circulatory and respiratory systems, altering the ability to carry out prolonged muscular work.

(4) Sex specific. The secondary sex characters develop and reproductive capacity is attained.

(5) Endocrine. The above changes result from alterations in the quantities of various hormones released into the blood stream by the endocrine glands, especially the pituitary, the gonads (ovaries in female and testes in male), and the adrenal cortex. The endocrine changes must precede the morphological or other effects which they produce, but will be more readily understood if we examine their effects first.

The Twelfth Oliver Bird Lecture was delivered by Professor Richard Doll, Regius Professor of Medicine in the University of Oxford, at the London School of Hygiene and Tropical Medicine on 19th March 1970. This was the last lecture to be given under the auspices of the Oliver Bird Trust, an account of which starts on page 359. Professor Doll was formerly Director of the MRC Unit of Medical Statistics, in which capacity he had exceptional experience in assessing the significance of changes in the incidences of abnormal conditions. The subject of his lecture was therefore highly appropriate to his special knowledge, as well as to current controversy and to the series of Oliver Bird lectures. The Journal of Biosocial Science is glad to publish this authoritative exposition of a most important problem.

The Sexual Offences Act, 1967, which made private homosexual behaviour between consenting males over the age of 21 years legal in England, marked a significant stage in the gradual change of social attitudes on this topic. A substantial body of opinion, including perhaps most of those personally affected, now takes the line that homosexuality is a common and relatively minor variant from the normal, that its occurrence is inevitable and that it is about time that the community learned to live and let live, recognizing that many ordinary folk, as well as many outstanding citizens, are unalterably homosexual.