SOME ASPECTS OF THE BIOLOGY OF HUMAN POPULATIONS 527 



Table hi 



Richmond Mayo-Smith and Thomas Allan Ingram give 

 the following corresponding figures for emigration from 

 Great Britain and Ireland, with the comment that: "Even 

 taking Great Britain and Ireland together, the loss by 

 emigration per annum has not been very large. " 



Besides the three primary biological factors of natahty, 

 mortahty and migration which influence the observed 

 growth of human populations there are various secondary 

 environmental factors which may play a part in determining 

 the final result. These are such things as food supply, 

 the economic situation in general and particular, social 

 forces of various sorts, and perhaps others. But it should 

 always be kept in mind that these are all secondary factors 

 from a biological point of view. They produce whatever 



