324 THE ASCENT OF MAN 



nearest ally of Reproduction, the newer experimen- 

 ters have discovered cases in which sex apparently 

 has been determined by the quantity and quality 

 of the food-supply. And in actual practice it has 

 been found possible, in the case of certain organisms, 

 to produce either maleness or femaleness by simply 

 varying their nutrition — femaleness being an ac- 

 companiment of abundant food, maleness of the 

 reverse. When Yung, to take an authentic experi- 

 ment, began his observations on tadpoles, he ascer- 

 tained that in the ordinary natural condition the 

 number of males and females produced was not far 

 from equal — the percentage being about 57 female 

 to 43 male, thus giving the females a preponderance 

 of seven. But when a brood of tadpoles was 

 sumptuously fed the percentage of females rose to 

 78, and when a second brood was treated even 

 more liberally, the number amounted to 81. In a 

 third experiment with a still more highly nutritious 

 diet, the result of the high feeding was more remark- 

 able, for in this case 92 females were produced and 

 only 8 males. In the case of butterflies and moths, 

 it has been found that if caterpillars are starved 

 before entering the chrysalis state the offspring 

 are males, while others of the same brood, when 

 highly nourished, develop into females. A still more 

 instructive case is that of the aphides, the familiar 



