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.

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 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.

In considering the evolutionary implications of the sex ratio (as opposed to the evolutionary implications of there being two sexes) a dual approach is required. On the one hand we need information about the variability of the sex ratio and to what extent that variability is genetically controlled, and on the other hand we need a theory which embraces the evolutionary consequences of a heritable variability, and which, ideally, is able to account for the observed situation by showing that it corresponds to a stable solution of the theoretical equations.

To summarize the findings presented here, only three of the five factors studied appear to be independently related to the sex ratio at birth. The significant negative birth-order effect, which in the first analysis accounted for a 2·6% shift in the relative odds of male birth, remained significant when adjustment for the race effect was provided in the second analysis. The magnitude of the effect was diminished by this adjustment, however, indicating that analysis for birth-order effects in the absence of adjustment for the race factor may lead to over-estimates of the importance of the birth-order factor.

The significant race effect detected in the second analysis resulted in a 3% lower relative odds for a Negro male birth than that for a white. This racial difference, coupled with the non-uniform distribution of Negro births by paternal-age and birth-order categories, appears to be the source of the mysterious ‘interaction effect’ between birth order and paternal age reported by Novitski & Kimball. The race effect remained significant after adjustment was provided for both the birthorder and socio-economic effects.

The subject of this talk is the ages of brides and grooms and how the relativity of the ages of such marriage partners has changed in England and Wales over the years. It is a well-documented subject in the sense that square tables showing the combinations of ages of marrying couples have been published annually since the middle of the nineteenth century. It is not well-documented in the sense that these plentiful data have attracted the research interest of demographers, economists or sociologists. Indeed, little work has been done up to now on this subject.

A good deal of the best-known work on the relationships between the sexes among humans has concentrated mainly on two aspects of this subject: either the physical or the psychological implications of sexual interaction have been quite widely discussed in literature easily available and often popularly presented. Without wishing to minimize the importance in its time of the work of Alfred Kinsey and his colleagues, one cannot help feeling, as Richards (1969) has recently observed in this journal, that since all primates copulate in much the same way, one is not going to achieve great insights by examining this in much detail. It is the humanity, not the animality, of man which provides the most significant part of his behaviour in this field. No one can write on this theme without paying due tribute to the work of Margaret Mead (1950), but much of it has concentrated on looking at ways in which upbringing in different societies makes people feel differently about their male and female roles.

I will preface these remarks by saying that I am a fierce believer in the fundamental equality of the sexes—after all, I am told that they are both necessary for the survival of the human race—or at least this seems to be so at the moment, though the way things are going it might at some time cease to be so. A second caveat is that I am not going to pretend to talk about the whole field of attainment, it would be inevitable that one would say too little about too much. However, if any of the audience wish to ask questions about any aspect of the topic in which they are interested I shall attempt to answer.

The employability of men and women in different industries is shown to be based mainly on traditional patterns and culture and by economic pressure and conditions of the labour market. Two probable reasons for the preference of men in some industries are: (1) their physical strength; (2) their lower labour turnover rate. One probable reason for the preference of women in some industries is their lower incidence of colour blindness. Other aspects of employability, including wages, anthropometry and productivity, are discussed.

I do not believe that I am the right person to give this Galton Lecture. I am not in the least a dyed-in-the-wool woman academic. To be that one has to have been man-and-boy in the job. Most of my colleagues at Oxford and sister colleagues at Cambridge could have given the lecture much better. Having written this introductory sentence, it was borne in on me that there were two separate breeds (I am not quite sure whether in this scientific milieu I should say species or genera) of academic women. At Oxford and Cambridge, at Durham, and up to recently in London, there has been the phenomenon (I cannot, in fact, think of any other classificatory term, for obviously one cannot use either breed or species or genera in the generally accepted sense about a single-sex organization) of associations of undiluted women academics, associations to be diluted by about 1972. In other universities, the female of the species is absorbed in the whole. Again, having reached this stage in my meditations, my sense of inadequacy in my present situation is slightly mitigated by the fact that I have at least had some experience of a community in which sex-differentiation was nominally not observed. Between my period as an Oxford undergraduate and my past 7 years as Principal of an Oxford women's college, I had 27 years at the University of London, though I must admit it was at an eccentric and utterly atypical institution.

Patterns of divorce behaviour in England are not well documented. Apart from the limited data provided annually by the Registrar General, and secondary commentaries on these, our knowledge comes almost entirely from a single paper which is now becoming historically dated (Rowntree & Carrier, 1958). There has been no social survey of a specifically divorced population, and the paper referred to is the only example of analysis based on court records. The present paper derives from work currently in hand which is utilizing survey interviews, court records, autobiographical materials and other documentary sources, to obtain new kinds of information about divorce. More specifically, what follows is based in part on data from the Registrar General's annual reports and, in part, on a provisional analysis of the court records of 1000 undefended divorce suits occurring in a provincial city during the years 1966–68.

The relation between sex and crime is an important and significant one. Broadly speaking, recorded criminality varies notably according to sex, being at a much higher level among males than females. It is men who are largely responsible for the planning and execution of large-scale crimes such as robberies. Serious recidivism, which presents such a problem in terms of penal care and treatment, is almost exclusively a masculine phenomenon—in a recent survey of crime in the UK, the incidence of serious recidivism amongst women is not even calculated (McClintock & Avison, 1968). The study of sex differences in criminality should, then, illuminate our knowledge of crime and its aetiology; it should also tell us something about sex differences in society in general.

Sex differences in psychiatric illness in earlier adult life are discussed. A random sample of elderly respondents were seen in their homes in order to examine neurotic reactions in the aged.

The relationship between neurotic symptoms, physical health, social data and sex were ascertained for the population as a whole.

Normal and late onset neurosis sub-groups were compared with regard to selected medical, psychiatric and social variables considered to have a bearing on neurotic reaction in the elderly. The variables discriminating best between ‘neurosis’ and normality were abnormal personality traits, physical ill-health and being female.

In the absence of any marked physical disability, being female was among the highest discriminators between the normal and neurotic groups. In the physically ill group, neither sex was more significantly represented than the other. Social factors were examined to explain the continuing preponderance of females in the late-onset neurotic group, but it was felt that they did not fully explain the differences observed.

The male is the weaker sex in nearly all disease categories and age groups. Sexual differences in mortality rates sometimes pose some interesting biological problems and warrant the interest of those concerned with the health of society. Males are undoubtedly the weaker sex. In contemporary, developed countries most mortality is man-made, the male being particularly adept at killing himself. In addition, men, the weaker sex, appear to reap some sort of vengeance on women, as the attitudes of doctors—and these are predominantly male attitudes—do not always lead to the most rational care of women undergoing the uniquely female risk of reproduction.