168 INTELLIGENT BEHAVIOUR 
condensation and concentration of experience by the formation 
of generic products through the reiterated emphasis begotten of 
recurrent situations having certain salient features in common, 
though differing in details; and fourthly, an increased 
plasticity of behaviour, especially in early life, enabling an 
animal to deal effectually with an environment far less 
simple than that to which the more stereotyped instinctive 
behaviour is fitted by inheritance to respond. And this 
evolution of intelligent behaviour is working its way up 
to, though as such it cannot reach, the succeeding phase 
of mental evolution in which the data, supplied by in- 
telligence, are treated with a new purpose for higher ends 
in the rational thought which seeks to explain the pheno- 
mena, and frame an ideal scheme of their relations and inter- 
connections. 
Two further points may be noticed. First, that it is during 
the early and plastic days or months of life that intelligence is 
setting its seal on animal behaviour, and stamping it with its 
distinctive character. Adult life is very much what youth has 
made it ; and old age is stereotyped through habit. In times 
of progress, the character of the race is determined by plastic 
possibilities of the young. Among them it is that the incidence 
of elimination makes itself felt, resulting in the survival of those 
whose intelligence can mould behaviour in accordance with 
the new circumstances of a wider life. 
Secondly, this selection of the intelligent involves the 
survival of those in whose higher brain-centres there is room 
for a greater range and variety of interconnection by means of 
associating fibres. It involves a selective survival of the 
larger and more finely organized brains. It is probable, as 
Professor Ray Lankester has recently indicated, that the 
ridiculously small-brained mammals and reptiles of the past 
were creatures of instinct with little capacity for intelligent 
control. Their lives were simple, and their enemies and com- 
petitors no better provided with higher brain-centres than 
themselves. Stereotyped instinctive behaviour sufficed to 
enable them to hold their own, and meet the requirements of 
