RAPID increase of the population of India has led to a demand for the inception of preventive measures. Birth-control there, and also in Great Britain, is, however, criticised by Col. C. A. Gill in a recent somewhat polemical paper (J. Hygiene, 34, 502; 1934). According to Col. Gill, population in an area ought to be considered not only from the point of view of numbers, but also from the occurrence of irregular changes or ‘movements' in the population, which, apart from migration, are largely determined by forces controlling the birth- and death-rates. Statistical methods forecasting future population ignore such ‘movements' of population, and estimates based upon population-growth curves have proved unreliable, for example, in India, and must be accepted with reserve. In a primitive community, prolificity as a means of race survival and an essential factor for progressive evolution is a paramount necessity, and artificial birth-control would constitute racial infanticide. Rural India, it is held, is such a community and is under-populated, and any State action to promote the practice of birth-control there is regarded as being a political crime and a biological blunder. In Great Britain, natural forces are now acting tending to limit increase of population, such as postponement of the average age of marriage and, possibly, a real decline in fertility. Since Nature requires a wide field of selection, nothing should be done to restrict the reservoir from which in the past many have sprung who have contributed greatly to human progress. The encouragement of birth-control among the masses, it is argued, is therefore to be regarded as being biologically reprehensible.