THE LAW OF HUMAN INCREASE. 39 



Among them are some lactucas (or lettuces), the Chinese arbor vitce, 

 and a number of Australian plants. Whenever this peculiarity has 

 been observed, it has also been found, on examination, that both sides 

 of the leaves were structurally alike. The property can be brought 

 out clearly under favorable conditions ; but it is liable to be modified 

 or marked, in the actual circumstances of growth, by any difference 

 in exposure to the sun or wind, on different sides of the plant. 



THE LAW OF HUMAN INCREASE. 



By NATHAN ALLEN, M.D.,LL. D. 



IT is almost one hundred years since the attention of T. R. Mal- 

 thus was first called to the subject of population and its changes. 

 As his views have had more influence than any other writer, it is well 

 to notice briefly what they were. His leading principle is, that " popu- 

 lation, when unchecked, increases in a geometrical ratio, while subsist- 

 ence increases only in an arithmetical ratio." He held that " popula- 

 tion is necessarily limited by the means of subsistence," and " invari- 

 ably increases where those means increase, unless prevented by some 

 very powerful and obvious check." He divides these checks into two 

 classes, the positive and the preventive : among the former are wars, 

 famine, diseases of all kinds, unhealthy occupations, extreme poverty, 

 great cities, etc. ; and in the latter class are abstinence from marriage 

 and sexual intercourse, from considerations of prudence. The last class 

 come more directly under the control of human agency. 



The next writer of any note was Thomas Doubleday, who published 

 in 1840 a work with this title : " The True Law of Population shown to 

 be connected with the Food of the People." The term "true law" 

 was undoubtedly introduced in opposition to the doctrine of Malthus. 

 Doubleday attempted to demonstrate that " wherever a species or 

 genus is endangered, a corresponding effort is invariably made by 

 Nature for its preservation and continuance, by an increase of fecun- 

 dity or fertility ; and that this especially takes place whenever such 

 danger arises from a diminution of proper nourishment," and that con- 

 sequently "the deplethoric state is favorable to fertility." Thus, 

 " there is in all societies a constant increase going on among that por- 

 tion of it which is the class worst supplied with food in short, among 

 the poorest." 



The April number of the "Westminster Review" for 1852 con- 

 tained an elaborate essay by Herbert Spencer, introducing a "New 

 Theory of Population," deduced from the general law of animal fer- 

 tility. He " maintained that an antagonism exists between individual- 

 ism "and reproduction ; that matter in its lower forms, for instance, of 



