This brings us naturally to the second part of our discussion--the consideration of the causes which lead to the increase or decrease of population. It is the most important part of our inquiry; for it is usually assumed that the British Isles will continue to send out colonists in large numbers, as it did in the last century, and the hopes of the imperialist that a large part of the world will speak English for all time depend on the untested assurance that the swarming-time of our race is not yet over. Our starting-point must be that the pressure of population upon the means of subsistence is a constant fact in the human race, as in every other species of animals and plants. There is no species in which the numbers are not kept down, far below the natural capacity for increase, by the limitation of available food. It may not always be easy to trace the connection between the appearance of new lives and the passing away of old, nor to say whether it is the birth-rate which determines the death-rate, or the death-rate the birth-rate. But it is well known that, wherever statistics are kept, the numbers of births and of deaths rise and fall in nearly parallel lines, so that the net rate of increase hardly alters at all, unless some change, which can easily be traced, occurs in the habits of the people or in the amount of the food supply. In civilised countries the greater care taken of human life, and its consequent prolongation, has reduced the birth-rate, just as in the higher mammals we find a greatly diminished fertility as compared with the lower, and a much higher survival-rate among the offspring born. The average duration of life in this country has increased by about one-third in the last sixty years, and the birth-rate has fallen in almost exactly the same proportion. The position of a nation in the scale of civilisation may almost be gauged by its births and deaths. The order in Europe, beginning with the lowest birth-rate, is France, Belgium, Sweden, the United Kingdom, Switzerland, Norway, Denmark, Holland, Germany, Spain, Austria, Italy, Hungary, the Balkan States, Russia. The order of death-rates, again beginning at the bottom, is Holland, Denmark, Norway, Sweden, Switzerland, the United Kingdom, Belgium, Germany, France, Italy, Austria, Serbia, Spain, Bulgaria, Hungary, Roumania, Russia. These two lists, as will be seen, correspond very nearly with the scale of descending civilisation, the only notable exception being the low position of France in the second list. This anomaly is explained by the fact that France having a stationary population, the death-rate in that country corresponds nearly with the mean expectation of life, whereas in countries where the population is increasing rapidly, either by excess of births over deaths or by immigration, the preponderance of young lives brings the death-rate down. We must, therefore, be on our guard against supposing that countries with the lowest death-rates are necessarily the most