ai6 



Laboratory Populations 



POPULATIONS 



The first example, taken from Richards 

 (1932), concerns the growth of pure strain 

 populations of the yeast Saccharomyces 

 cerevisiae. Figure 109 shows this trend for 



four different yeast cultures over 1200 

 hours of observation. The abscissa records 

 the number of cells in 1/250 mm'. The 

 asymptote is attained between 180 and 200 

 hours. Subsequently (and this is the per- 

 tinent point for present purposes) an equi- 



100 



en 

 o 



_J 



2500h- 

 2000 

 15001— 

 1000 



2 5001- 



SECOND HYPOTHESIS 



LOWER ASYMPTOTE 



PRESENT CYCLE ==^_^445 MILLIONS 



13 

 CL 

 O 

 CL 



3 2500 1— 

 9 2000 



1500 



1000 



500 



THIRD HYPOTHESIS 



_LOWER ASYMPTOTE 



"present CYCLE = 



445 MILLIONS 



/ \ 



DATE 

 1930 



1630 



DATE 



-r 



100 



DATE 

 1930 

 / 



± 



1630 

 DATE 



100 



TIME SCALE OF MAN'S POPULATION HISTORY 



(IN THOUSAND YEAR UNITS ) 

 Fig. 108. Three alternative hypotheses to account for the growth of the human population 

 of the world. (The slight backward bend displayed by each of the last three logistics in the 

 three diagrams is inaccurate. ) ( From Pearl and Gould. ) 



