It is only of recent years that the eugenic importance of a considerable interval between births has been fully recognised, as regards not only the mother--this has long been realised--but also the children. The very high mortality of large families has long been known, and their association with degenerate conditions and with criminality. The children of small families in Toronto, Canada, are taller than those of larger families, as is also the case in Oakland, California, where the average size of the family is smaller than in Toronto.[12] Of recent years, moreover, evidence has been obtained that families in which the children are separated from each other by intervals of more than two years are both mentally and physically superior to those in which the interval is shorter. Thus Ewart found in a northern English manufacturing town that children born at an interval of less than two years after the birth of the previous child remain notably defective, even at the age of six, both as regards intelligence and physical development. When compared with children born at a longer interval and with first-born children, they are, on the average, three inches shorter and three pounds lighter than first-born children.[13] Such observations need to be repeated in various countries, but if confirmed it is obvious that they represent a fact of the most vital significance. Thus when we calmly survey, in however summary a manner, the great field of life affected by the establishment of voluntary human control over the production of the race, we can see no cause for anything but hope. It is satisfactory that it should be so, for there can be no doubt that we are here facing a great and permanent fact in civilised life. With every rise in civilisation, indeed with all evolutionary progress whatever, there is what seems to be an automatic fall in the birth-rate. That fall is always normally accompanied by a fall in the death-rate, so that a low birth-rate frequently means a high rate of natural increase, since most of the children born survive.[14] Thus in the civilised world of to-day, notwithstanding the low birth-rate which prevails as compared with earlier times, the rate of increase in the population is still, as Leroy-Beaulieu points out, appalling, nearly half a million a year in Great Britain, over half a million in Austro-Hungary, and three-quarters of a million in Germany. When we examine this excess of births in detail we find among them a large proportion of undesired and undesirable children. There are two opposed alternative methods working to diminish this proportion: the method of preventing conception, with which we have here been concerned, and the method of preventing live birth by producing abortion. There can be no doubt about the enormous extension of this latter practice in all civilised countries, even although some of the estimates of its frequency in the United States, where it seems especially to flourish, may be extravagant.