26 



THE HISTORY OF ECOLOGY 



ades of the niiieteentli century. Doubleday 

 (1841), stimulated by his skepticism con- 

 cerning the validity of the population 

 theory of Malthus, brought forth his "true 

 law of population." He said in part (p. 6) : 



"The great general law then, wliich, as it 

 seems, really regulates tlie increase or decrease 

 both of vegetable and of animal life, is tiiis, 

 that whenever a species or genus is endangered, 

 a corresponding effort is invariably made by 

 nature for its preservation and continuance, by 

 an increase of fecundity or fertility; and that 

 this takes place whenever such danger arises 

 from a diminution of nourishment or food, so 

 that consequently the state of depletion . . . 

 is favorable to fertility; and that, on the other 

 hand, . . . the state of repletion, is unfavor- 

 able to fertihty, in the ratio of intensity of 

 each state, and this [holds] probably through- 

 out nature universally, in the vegetable as well 

 as in the animal world . . . ." 



Doubleday was mainly concerned with 

 human phenomena. He accurately detected 

 the fact that the well-to-do and rich repro- 

 duce less rapidly than the poor, and inac- 

 curately thought that this human situation 

 and similar phenomena in plants and 

 animals were wholly expUcable in terms of 

 the effects of overrich mineral nutrients on 

 plants and overfeeding with domestic ani- 

 mals, including man. 



The next contribution, that of WiUiam 

 Farr, did not grow out of the same set of 

 considerations that had intrigued Malthus, 

 Quetelet, Verhulst, and Doubleday. Farr 

 was especially concerned with mortahty. In 

 1843 he discovered that, within limits in 

 England, there was a relation between the 

 density of the human population and the 

 death rate such that mortahty increased as 

 the sixth root of density. Farr returned to 

 the problem in 1875 and tested his earlier 

 discovery against population and mortahty 

 data from all districts of England and 

 Wales for the years 1861 to 1870, finding 

 that when the districts were listed in the 

 order of their mortahty, the latter always 

 increases with the density, but less rapidly. 

 In general terms, Farr's rule states that if 

 the death rate is represented by R and the 

 density of the population per unit area by 

 D, then R = ^D"*, where c and m are con- 

 stants. 



Brownlee (1915) rehabihtated this rule 

 by showing that the statistics used by Farr, 

 which came from the decade 1861 to 1870, 

 compared favorably with those from the 



decade 1891 to 1900. The only correction 

 needed arose from tire improvement of san- 

 itation in the intervenmg years. 



It is easy to jump ahead of our chiono- 

 logical story. In 1852 Herbert Spencer pub- 

 hshed an outhne of "A Theory of Popula- 

 tion, Deduced from the General Law of 

 Animal Fertihty," which he later incor- 

 porated in his Principles of Biology (1867) 

 and expanded to make a whole section of 

 that work. The essence of his later state- 

 ment is: 



"Individuation and Genesis are necessarily 

 antagonistic. Grouping under the word Indi- 

 viduation all processes by which individual life 

 is completed and maintained, and enlarging 

 the meaning of the word Genesis so as to in- 

 clude all processes aiding the formation and 

 perfecting of new individuals; we see the two 

 are fundamentally opposed. Assuming other 

 things to remain the same— assuming that en- 

 vironing conditions as to cUmate, food, enemies, 

 etc., continue constant; then, inevitably, every 

 higher degree of individual evolution is fol- 

 lowed by a lower degree of race multiplication, 

 and vice versa. Progress in bulk, complexity, 

 or activity involves retrogress in fertihty; and 

 progress in fertihty involves retrogress in bulk, 

 complexity, or activity." 



We sympathize with Doubleday, who 

 complained (1853, p. xxix) about an earher 

 version of this idea: "The author will now 

 venture a few brief remarks on positions of 

 a very erudite review of the 'True Law of 

 Population' . . . pubhshed . . . under the 

 name of 'Herbert Spencer.' It is not easy to 

 evolve the exact doctrine of the reviewer 

 from the load of learned diction ..." 



Stated simply, Spencer's ideas were that 

 when the amount of energy is hmited, the 

 greater the proportion used in the growth 

 of nutritive aspects of the individual, the 

 less there is left for reproduction. Double- 

 day found this suggestion entirely unac- 

 ceptable. 



Darwin took over without criticism the 

 whole of the Malthusian doctrine as regards 

 the geometric ratio of population growth 

 and the resulting struggle for existence. He 

 documented these ideas extensively with 

 data from nonhuman as well as from human 

 populations. The use he made of them is 

 well and generally known. In the Origin of 

 Species he also clearly recognized that 

 populations exist as units. Thus the evolu- 

 tion of instincts of neuter insects can be 

 explained on the ground that the colonies 



