318 



POPULATIONS 



cross the North Sea, usually from Hull, 

 England, to seaports on the Dutch, German, 

 and Scandinavian coasts. 



Figure 110 shows a particular series of 

 records covering three years of observations 

 made with the plankton recorder over 250 

 miles of the "Copenhagen line." It is of in- 

 terest for our present purpose since the 

 Rhizosolenia populations exhibit an equilib- 

 rium during the February to September in- 

 tervale of 1933 and 1934 characterized by 

 its relative constancy, despite the small to- 

 tal size of the population (in some cases the 

 populations appear to fall essentially to 

 zero) and despite the fact that this species 

 is capable of large fluctuations. The latter. 



It is possible, however, to select arbi- 

 trarily an illustration that shows a semi- 

 equilibrium from the admirable collection 

 of demographic data assembled by Linder 

 and Grove (1943). The yearly census rec- 

 ords for the state of Delaware from 1900 

 through 1940 provide a fair example. When 

 the number of males and females of all 

 races other than white is plotted by years, 

 a graph is obtained (Fig. Ill) that shows 

 that this population component is quite 

 stable. From 1900 to 1917 the population 

 is in striking equilibrium. There is a slight 

 depression and recovery during the next ten 

 years and then a gradual but consistent 

 rise from 1927 on. The latter component 



36.000 — 

 <n 3 5,000- 

 °34p00- 

 a 33,000 - 

 ^ 32,000 - 

 5 31,000 



CD 



§30,000 

 29.000 



28000 



I I I I 



.1 I I I I \ \ I I I 



1900 



10 



20 

 YEAR 



'30 



J I I I L 



40 



Fig. ill. Population trend of "nonwhite" inhabitants of the state of Delaware, 1900 to 1940. 

 Note that base line of graph is 28,000 persons instead of zero. 



especially those associated with the seasons, 

 will be mentioned later in this chapter. 



Human Populations 



Most contemporary human populations 

 for which modern census data exist have 

 not yet attained their maximum growth, so 

 that it is impossible to report an equihbrium 

 state for them. This is true, for example, 

 for the total population of the world and 

 for the United States as well as for numer- 

 ous other political units. Undoubtedly, there 

 have been certain occasions in the past 

 when human populations have reached an 

 equihbrium and held it for a considerable 

 period of time, but accurate data to illus- 

 trate this point are hard to find.* 



* It is a likely assumption that native popu- 

 lations everywhere, beyond the influence of 

 modern technology and isolated from each 

 other, have been in equilibrium, more or less. 

 Illustrations are afforded by New Guinea, New 

 Zealand, or practically any South Sea Island. 

 Consult also Pearl (1930). 



is probably a true departure from the 

 equihbrium in that it represents, for one 

 reason or another, a real growth. The mean 

 population size over this forty-one year 

 period is 31,715 persons. The lowest year, 

 1921, is 7.1 per cent below this mean, and 

 the highest year, 1940, 13.4 per cent above 

 the mean. This example is included here 

 merely to show that it is possible for hu- 

 man populations to attain and maintain 

 something of an equilibrium. It will be in- 

 teresting, of course, when demographers at 

 some future date study this question after 

 the populations of large countries and the 

 world as a whole attain their asymptotic 

 size. 



FLUCTUATIONS 



Whereas the problem of presenting ex- 

 amples of equilibrium and oscillation is one 

 of trying to find adequate examples, that of 

 presenting population fluctuation is one of 

 exclusion. The implication here, of course, 

 is that populations are commonly found in 



