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.