THE OUTLOOK 
been possible to ascertain it exactly?” For the 
quinquennium 19o6 to 1911 there: were accurate 
statistics for twenty-six countries, and these gave a 
rate over all of 1-159 per cent. per annum. For the 
century 1800 to 1900, however, there is no doubt that 
the rate of increase was not even 1 per cent. Roughly 
it was about only 0-864 per cent.! Thus, although 13 
per cent. is approximately the recent annual rate of 
increase for twenty-six countries, it is only about six- 
sevenths of a per cent. for the whole world. We get 
an idea of the significance of these rates by asking 
in what time the population would double itself, 
if they held good. It is sufficient to mention that 
1 per cent. means doubling in 69-66 years.2 Hence, 
supposing Man started from a single pair, it has to 
be doubled only thirty times to give a population of 
2,147,483,048, that is more people than the world yet 
contains. This means that a rate of increase of 1 per 
cent. would give a population of over 2147 millions 
in 2090 years. 
We get also, and very readily, a clear idea of the 
extraordinary slowness of the average rate of growth 
of the world’s population by making any plausible 
assumptions as to the length of time Man has been on 
the planet. If this was only 100,000 years, and he 
sprang from one pair only, then his average rate of 
increase was only about one-fiftieth of a per cent. 
annually, or 2 per 10,000 per year. If, however, he 
has been on the earth as much as one million years, 
his increase-rate was only one five-hundredth of a 
per cent., instead of about 1 per cent. as at the 
beginning of this century. In other words, every 
1 See Mathematical Theory of Population, Appendix to Report on 
1911 Australian Census, G. H. Knibbs, p- 31. i 
? The rate 0-864 per cent. doubles the population in 80-54 
years; 1-000 per cent. in 69-66 years; and 1-159 per cent. in 60-22 
years.