The fitness of human zygotes depends on both biological and demographic parameters. Some of the demographic parameters are changing at present in this country and accurate estimates of them are not available but this imprecision has no great bearing on the estimate of fitness offered below.

Of 100 human zygotes, now, in this country, it is estimated that embryonic and early fetal loss (before the end of the 3rd month) accounts for 44; induced abortion, 7; late fetal loss (after the 3rd month), 4; and mortality between birth and maturity, 1½. Of the remaining 43½ who reach maturity, it is estimated that 8 fail to reproduce, leaving 35½ who do reproduce.

The standard error of this estimate must be large because of the large standard error of the estimate of the incidence of natural reproductive wastage from which it was derived.

Using the ISCC and the Burnham-Clark-Munsell tests, the colour aptitude and colour memory of a group of art students have been compared with a control group, matched for sex and age. The results of the colour aptitude test show that, for the men, but not for the women, the art students performed significantly better than the control group. With the colour memory test, there was no significant difference between the art students and the controls but, overall, the women had better results than the men.

Eleven-year-old boys and their parents from southern Ontario, Canada, were used to examine relations among sibling constellation variables, social status indicators and a set of parent-sibling interaction variables which were highly predictive of mental ability performance. A two-term equation including father's occupation and either sibsize or the inverse of sibsize parsimoniously accounted for as much significant variance in the parent-sibling variables as complex many-termed equations. Within each socioeconomic group the amount of parent-sibling interaction decreased as the family size increased. It was also found that in high social status groups the amount of interaction in large families was greater than in small families from lower social status groups. By using refined environmental measures the study provides an increased understanding of the relations between social status, sibling constellation variables, family environment and cognitive performance.

The personality dimension ‘introversion-extraversion’ as a factor in the socialization of approved school delinquents has been examined. Contrary to expectations of certain theorists, the allegedly more easily socialized introvert is usually not under-represented in delinquent populations. The possibility was investigated, therefore, that the level and type of attention an individual receives during the socialization process is a function of personality factors thought to reflect socialization capacity. The findings supported this hypothesis from which it would follow that a significant correlation between delinquent behaviour and such personality characteristics is improbable.

The problem of involuntary childlessness and its effect on marital happiness has been studied in an investigation involving interviews with 75 childless couples and a matched control of 75 couples with children. Marital happiness in various phases of the couple's relationship is plotted; in childless women this is seen to fall to its lowest ebb during the phase immediately before the problem is brought to the attention of the doctor, whilst in men it occurs whilst waiting for the medical diagnosis to be made. It seems that whilst childless marriages in themselves are not necessarily less happy than those with children (though all the childless couples interviewed had sought to change their situation by seeking medical help) such marriages are based on a different equilibrium from that of couples with children. In childless marriages there is often closer communication between the partners and a greater degree of communis opinio. People with children are sometimes over-careful in their approach to those without children. Attitudes and behaviour with regard to fidelity are seen to differ; the childless couples interviewed were less permissive in this respect than those with children. Alternatives in the form of artificial insemination, adoption, careers and pets are briefly considered.

The prevalence of vaginal mucus at the time of ovulation was recorded by 166 women in 1800 cycles along with their basal body temperature (BBT). Seventy-five per cent of women observed mucus in every cycle, 21% in some cycles only and 4% never saw mucus. Three women conceived in cycles in which there was no mucus. The time of first appearance of mucus has been related to cycle length and to the time of rise in BBT. The implications of these findings for the use of the mucous method of avoiding conception is discussed.

Gross motor performance data were secured from boys and girls in special education classes for the minimally brain injured. By factor analysis two gross motor factors were identified, one a strength-maturation component, and the other general motor ability. In comparison groups of educable mentally retarded children from the same school districts, the same factors were apparent, though the order of extraction was reversed.

Using data from the 1960 US census of population, migrant and non-migrant families are compared, over the period 1955–60, for family size in three residence groups of whites and non-whites. Migrant families in both colour groups are found to have a higher mean number of children under 6 years of age than do the non-migrants and a small differential is maintained even after indirect standardization for age of family head. Non-migrant families have a higher mean number of older children but this excess decreases after standardization. It is concluded that migration does not interfere with childbearing and that, on balance, migrants do not have fewer births.

Fifty years ago, in the early 1920s, Marie Stopes published her books on childbearing, contraception and sex, and immediately became famous. Indeed recently when an American jury was asked to select the 25 most influential books published in the previous 50 years, Marie Stopes was one of a list of twelve authors which included Marx, Lenin, Freud, Einstein, William James and Hitler.

I was fortunate to read her books when I began my career as a practising obstetrician in Glasgow in 1928 and I propose to discuss the changes in human reproduction which have occurred in the last 50 years under the headings of three of Marie Stopes' best known books: (1) Radiant Motherhood, (2) Planned Parenthood and (3) Married Love.