THE CHANGING WORLD OF LIFE 545 



veloping new and better ways of destruction and, unless there is a con- 

 stant improvement of methods of resistance, extinction is a certainty. 



At the opposite end of the scale we find the large, slow-breeding ani- 

 mals that produce a much smaller number of offspring, but give pro- 

 tection to those that are produced to reduce the loss during the early 

 stages of life. One of the best illustrations of such slow breeding ani- 

 mals is the elephant. The gestation period of elephants is about two 

 full years, so the young elephant has the protection of its huge mother's 

 body for the first two years of its life, and it is large enough when born 

 to be able to protect itself very well. However, even then, the mother 

 shows a solicitude for her baby that is unexcelled in the entire animal 

 kingdom, and woe betide any creature that is rash enough to molest a 

 young elephant in the presence of its mother, and she is always near 

 enough to come running at the slightest squeal from her baby. As if 

 this were not enough, one of the other female elephants in the herd that 

 does not have a baby of her own will aid in the protection of this one. 

 This second female is called the "auntie," and between the two there 

 isn't much chance of harm coming to the precious infant. This pro- 

 tection continues for years until the young elephant is large enough to 

 hold its own among other members of the herd. 



It will be about ten years before the mother will be able to give birth 

 to a second baby under such a system. However, because of the long 

 life of elephants a single female will have seven or eight offspring during 

 her lifetime. On the average, only two of these will live, so there is 

 natural selection and elimination of the least fit among the elephants 

 just as there is among the bullfrogs. 



Among human beings, natural selection works to eliminate the unfit 

 just as surely as it does among the other forms of life. By means of 

 medical science and social welfare agencies we have been able to reduce 

 the number eliminated in the highly civilized countries, but it is im- 

 possible to save those least adapted to our environment. We have bal- 

 anced this with a reduced birth rate, so that there is not a great popula- 

 tion increase in these countries. In the less civilized countries, how- 

 ever, the birth rate and death rate continue at the same high level found 

 in other forms of animal life. 



Sexual Selection 



This is a phase of selection that is of great importance in maintain- 

 ing the vigor of a race. It does not work by the complete extermina- 

 tion of the least fit, but by eliminating reproduction of the least fit. It 

 is most effective among the males because most of the females manage 



