172 BEGINNINGS OF INTELLIGENCE 
shall therefore consider the question purely from a phy- 
siological standpoint. Viewed objectively we find that 
in an animal’s behavior certain acts when once performed 
tend to be performed with greater readiness under similar 
conditions a second time, while other acts once performed 
tend under similar conditions to be inhibited. This prob- 
lem of learning, Baldwin observes “is the most urgent, 
difficult and neglected question in the new genetic psychol- 
ogy.’ Spencer with his characteristic insight into funda- 
mental problems has grappled with it and has attempted 
to give a physiological explanation. Pleasure, according 
to Spencer, is the concomitant of heightened nervous dis- 
charge; pain the concomitant of lessened discharge. In an 
animal with a diffuse discharge of its nervous energy result- 
ing in random movements, some of these movements bring 
a heightened nervous discharge with its psychic accompani- 
ment of pleasure. This tends to reinforce the movement that 
brought the increase of nervous energy and to cause it to be 
repeated. Responses resulting in pain tend on account of the 
diminution of nervous discharge that follows to be discon- 
tinued, and in this way the organism is kept repeating certain 
acts and avoiding others. “Along with the concentrated 
discharge to particular muscles,” says Spencer, ‘the gang- 
lionic plexuses inevitably carry off a certain diffused dis- 
charge to the muscles at large, and this diffused discharge 
produces on them very variable results. Suppose, now, 
that in putting out its head to seize prey scarcely within 
reach, a creature has repeatedly failed. Suppose that along 
with the group of motor actions approximately adapted to 
seize prey at this distance, the diffused discharge is, on 
some occasion, so distributed throughout the muscular 
system as to cause a slight forward movement of the body. 
Success will occur instead of failure; and after success will 
