BIOLOGICAL FOUNDATIONS 19 



we come to the birds, parental love becomes of enormous 

 importance* Any species of bird that neglected its 

 young would soon become extinct. Think for a moment 

 of the enormous amount of loving care that is needed to 

 rear a brood of little birds* Even before the eggs are 

 laid the nest has to be built and a comfortable home 

 prepared* Then, when the eggs are laid, the mother bird 

 has to sit on the eggs, whilst the father bird fends for the 

 two ; and sometimes the father bird will take his place 

 on the eggs, in order to give the mother bird a change* 

 And even when the little ones are hatched out, a vast 

 amount of loving care is still needed in order to rear 

 them* Now all this means self-sacrifice* Moreover, 

 every variation in the direction of less self-sacrifice, less 

 love, a lower sense of parental responsibility, will be to 

 the disadvantage of the offspring, so that this variation 

 is not likely to be handed on by heredity to the next 

 generation* But any variation in the direction of 

 more love will be to the advantage of the offspring, so 

 that this variation is much more likely to be handed on 

 to the next generation* And what is true of the birds, 

 is still more true of the mammals* Take, for example, 

 the domestic cat ; what a splendid mother she makes ! 

 No sacrifice seems too great for her to make on behalf of 

 her kittens* She will even rush into a burning house to 

 rescue them* But although the cat's self-sacrifice is 

 almost unlimited in degree, it is strictly limited in time* 

 Before long, the kittens are old enough to fend for them- 

 selves, and then the cat's love for them is apt to change 

 ro green-eyed jealousy* And the same is in large measure 

 true of all mammals until you come to Man* And here, 

 as we should expect from his far higher evolution, a far 

 greater degree of self-sacrifice is demanded from him* 

 Take, for example, a child three years old* How entirely 

 dependent he is on the loving care of his parents ! 

 Compare him with a horse three years old ; almost ready 



