148 evolution: the ages and tomorrow 



stages. Instincts are like functional organs and have been pro- 

 duced through mutational and other genetic changes by nat- 

 ural selection. In ants all intermediate steps of this evolution 

 have been lost, but in the bees there are many living repre- 

 sentatives of earlier stages from the entirely solitary to the 

 highly communal. There are bees with no trace of social life 

 other than seasonal gregarious associations. In these species 

 the females store up food and then deposit their eggs on the 

 food pile, leaving the grubs to hatch out and take care of 

 themselves. The next step is seen in Halictus and related 

 species where the original female remains in the spring of 

 the year with the first eggs which she has laid on a food pile. 

 The eggs hatch out finally and the young bees go about the 

 business of collecting food and rearing more young. There 

 is a sort of colony life without division of labor that lasts all 

 summer. In the fall, however, the loose social group breaks 

 up completely, and the females that survive the winter must 

 start the cycle all over again. 



Bumblebees are just above this level in their organization. 

 Communal life is for one season only, but there are the be- 

 ginnings of a division of labor, and more specifically differ- 

 entiated instincts are evolving. The colony is started in the 

 spring by a female which has survived hibernation. She digs 

 an underground nest with a few rude cells in which she lays 

 a number of eggs, after having made up a food pile of pollen 

 and honey. The food supply for each set of eggs is inade- 

 quate even though the lone female works overtime, adding 

 to each ceil such stores as she finds. The grubs develop into 

 stunted and sterile neuters, because the gonads in bees need 

 good nutrition for full functional development. The neuter 

 workers at once solve the problem of food supply. They 

 sally out in search of honey and pollen, and soon the future 

 grubs receive all and more than is necessary for full-size, 

 fertile development. In this way, as the season goes on, all 

 transitions between sterile workers and fertile queens are 

 produced. As the summer ends there are plenty of the fe- 



