140 evolution: the ages and tomorrow 



cally and with specific responses in a predetermined se- 

 quence. These specific responses strike the human observer 

 as being beautifully adapted to certain conditions in the in- 

 sect's life, but sometimes they default badly when condi- 

 tions are changed, even though a faint glimmer of intelli- 

 gence might save the situation. 



The "inborn tricks" of the insect make its life easier 

 under the normal conditions which called forth the adapta- 

 tion, but they are useless or even dangerous in new situa- 

 tions. On the other hand, the greater reliance of the verte- 

 brate on learning by experience, bitter or not, opens up a 

 far greater range of adaptive possibility. Under ordinary 

 circumstances the faults of fixed instinctive patterns are not 

 troublesome to the organism, but they can sometimes ap- 

 pear very glaringly and ridiculously faulty to the human 

 experimentalist. 



Fabre describes the behavior of the digger wasp Sphex 

 which hunts crickets. Sphex brings a paralyzed cricket to 

 her burrow, she leaves it on the threshold, and enters for a 

 moment to look the place over, then emerges and drags the 

 cricket in. While one of these wasps was inside, Fabre 

 moved the cricket a few inches awav from the door. The 

 wasp emerged, found the same cricket after a moment or 

 two, dragged it back up to the edge of the burrow, left it, 

 and entered. Fabre again moved it a few inches away. x\gain 

 the wasp found it, dragged it back to the edge of the bur- 

 row, left it, and entered. Again and again Fabre moved the 

 cricket and observed the same results. Apparently the in- 

 stinct demands a sequence of drag the cricket to the door, 

 enter and look the place over, emerge and haul the cricket 

 in— a cogwheel-like arrangement of successive actions, each 

 setting off the next and tolerating little variation. In a cir- 

 cumstance like this the wasp does finally, after repeated tri- 

 als, drag the cricket straight into the burrow. 



The Peckhams describe another typical case of a rigid, 

 sequence instinct in one of the spider-hunting wasps, which 



