This study analyses, for the dynamic economy of a typical less developed country (LDC), the significance for economic development over 30 years of gradual reductions in age-specific fertility rates (assumed to result from a government-supported birth reduction campaign).

The computer results, using parameters typical of poorer LDCs, include the following:

1. A modest birth control programme, costing perhaps 30 cents a year per head of national population, can raise average income over only 15 years by almost twice the percentage that it would rise without birth control;

2. Such a birth control programme, including more exposed couples every year until half of them are practising contraception, yields an undiscounted return on cost of 13 times in 5 years and 80 times in 30 years;

3. The value of permanently preventing the birth of a marginal infant is about twice an LDCs annual income per head;

4. Without birth control, to achieve similar rises in income per head, the rate of productive innovation would have to be about 1½ times the typical rate assumed;

5. Saving propensities would have to be from 2 to 3 times as great as are assumed typical if similar income increases per head are to be realized without birth control.

The model employed uses age-specific death, fertility, and consumption rates for an annually changing age distribution of population. It also uses a national production function that takes into account the changing stocks and productivities of labour and capital, saving propensities that vary with disposable income and the rate of productive innovation. Consequently, it can trace, in more detail than any demographic–economic model yet described in the literature, the incidence of whatever fertility reductions may result from government or private birth control programmes.*

From statistics on Australian confinements during the period 1944–63 it seems that the following conclusions can legitimately be drawn:

(1) The proportion of multiple births increases with increasing age of mother up to about age 37, turns, and decreases thereafter.

(2) The proportion of multiple births increases with increasing age of father up to about age 34–38 and is fairly constant thereafter.

(3) The variation with age of father, however, only arises because of the high correlation with age of mother which is the determining factor.

(4) The proportion of multiple confinements increases with birth order. This effect holds for all ages of mother except those over 40 where there is no significant variation.

(5) The proportion of multiple confinements decreases from the first year of marriage to the second, then increases steadily to a maximum after about 15 years of marriage and then decreases slightly.

(6) The proportion of binovular twins increases steadily with increasing age of mother up to about age 37, turns, and thereafter decreases steadily.

(7) The proportion of monovular twins increases slightly with increasing age of mother up to about age 37 and is fairly constant thereafter.

(8) From the small amount of data it appears that the proportion of triplets also increases with increasing age of mother.

It is an observed fact that human populations differ in genetic composition. Some of the inherited diversity is due to combined effects of many genes. Although it would be interesting to know the magnitude and nature of the genetic contribution to some characters under polygenic control, such as intelligence or physique, environmental effects may be so great that no genetic analysis is possible—as Thoday has pointed out earlier in this symposium. With other polygenic characters, such as skin colour, the genetic component is more obvious but still difficult to analyse precisely. The number of genes involved, their frequency and dominance have not been established. This is one of the reasons why selective effects on such characters are not readily measured, although they probably exist.

Reproductive performance and some of the more important features of their progeny were studied in 755 radiologists and in 346 laboratorians as controls in order to investigate the possible genetic injuriousness of ionizing radiation. Significant differences were found only in fertility: the fertility of female radiologists was significantly lower than that of the female laboratorians and of the wives of male radiologists. This phenomenon is probably explained by a more extended use of the methods of birth control by female radiologists due to roentgenophobia.

A longitudinal study of the growth of a cohort of 229 infants born in a rural area in Jamaica and followed to their 4th birthdays is described, and this paper reports analyses of the anthropometric measurements.

Moderate impairment of growth affected the majority of children and was most marked between the ages of 3 and 15 months. Severe impairment occurred in boys more often than girls and in this comm unity was rarely attributable to disease.

The concept of weight faltering has been investigated in some detail; failure to gain weight for a period of 6 months occurred in almost half the children but was not, by itself, a useful prognostic index of malnutrition; it occurred commonly in children of above average weight whose subsequent growth was normal.

The provision of intensive care at specially appointed child welfare clinics did not completely prevent the development of serious malnutrition.

The fall in the birth rate in Australia, from 23·6 per 1000 population in 1946 to 19·4 in 1967 is analysed according to various biosocial factors: the age composition of the female population and the age incidence of marriage in relation to it, the timing of births, the size of completed family and the overall effect of the variables.

It is both a pleasure and an honour for me to participate in one of the stimulating Symposia arranged by the Eugenics Society. But it was with some diffidence that I agreed to speak on the topic of miscegenation: a topic which is so complex, so illunderstood, so charged with emotion. Yet miscegenation is of obvious interest to all who concern themselves, as members of the Eugenics Society do, with human biology, human society and the future of humanity. It is a topic worthy of study, and a topic which needs to be discussed frankly if myths are to be dispelled, confusion to be reduced, and problems resolved. For miscegenation has been a continuous process since the earliest times: it is nothing new. As my own guru, Professor E. A. Hooton, was fond of saying, ‘When peoples meet they sometimes fight, but they always mate.’

The first Hammond Memorial Lecture was given in London in March 1969 by Dr C. P. McMeekan, CBE, formerly Director of the Ruakura Research Centre in New Zealand, afterwards on the staff of, and currently consultant to, the World Bank. Apart from its special interest to those engaged in animal science, the lecture contained much of general interest to natural and social scientists and we are grateful to Dr McMeekan, the Hammond Memorial Trustees and the British Society for Animal Production, under whose auspices the lecture was delivered, for permission to print a substantial portion of it in the Journal of Biosocial Science.

Some of the selected material is provocative. For instance, it would be interesting to know the basis of the assumption that world population having risen to 6000 million by the end of this century, will then stabilize. Again, many will disagree with the estimates of unused usable land. But all of the material stimulates thought and we are glad to have the opportunity of publishing it.

After discussing the outstanding achievements of Sir John Hammond and the progress of animal science generally, Dr McMeekan continued:

Anencephaly and spina bifida cystica, malformations of the central nervous system, are due to failure of closure of the neural tube. These malformations are a major cause of stillbirth, infant death and (in the case of spina bifida) of childhood morbidity in Britain today.

Their aetiology is not known in detail. There are, however, indications from family studies and from the striking racial variation in their incidence (which is in part at least maintained after migration) that genetic factors are important in their causation. There is also evidence from maternal age and birth order effects, secular and seasonal variation, and social class effects that environmental factors also are important in their aetiology.

Much of our understanding of the biological differences between races has come with the development of human genetics. Surveys have established the frequencies of genetic characters known to be under the control of single genes and independent of environmental modification; comparisons of these frequencies in different populations have led to the resolution of many of the earlier outstanding problems of affinities between races and, with the support of experimental and associated investigations, to the identification and measurement of the processes that have given rise to race formation. With this information we can begin to appreciate the extent to which apparent differences are due to racial heritage and to environmental influences.

313 pairs of brothers and 296 pairs of sisters were compared by one or both parents in a postal questionnaire. For 495 pairs independent questionnaires were completed by father and mother, and agreement between parents was good.

There was a marked tendency for the first-born child to be rated as less fond of cuddling; he was also easier to train, worked harder at school, set himself higher standards, and was more serious, methodical, law-abiding, tidy and less impulsive; he learned to talk and read at a younger age and was rated as having more natural ability at schoolwork. These three groups of first-born attributes were relatively independent; for instance, even the first-born with less ability at schoolwork were given more responsibility at school. In the 152 pairs which did not contain a first-born, little birth order effect could be found, whether or not the elder was the eldest of his or her sex.

There was a slight tendency for the broader, fatter and more muscular child to be less nervous and highly strung, but otherwise differences in physique were not related to differences in behaviour. Abilities at schoolwork, games, music and painting were not related. Tendency to anxiety and depression was related to lack of sociability; to stubbornness and lack of practicality; to angryness but not the bottling up of anger; to level of aspiration but not the possession of abilities or good looks. These relations of anxiety and depression in a normal sample closely parallel the items which distinguish psychiatric patients from their healthy siblings.

Man's ability to perform his daily round of work is a complex matter and depends upon an optimal function of numerous organs and their integration. Intellectual ability, motivation and emotional stability play a great, and sometimes decisive, role in work performances.