HEREDITY AND EVOLUTION 257 
area contains about as many plants and animals as it can sup- 
port. On the average, then, each plant produces one offspring 
which reaches maturity and takes the place of its parent. Every 
mature plant, however, produces many seeds, each of which 
contains a young plant. If all the seeds produced by one plant 
and its descendants should come to maturity, the descendants 
would soon be numerous enough to cover the earth. Likewise, 
if all the descendants of a pair of animals lived to old age, there 
would be enough of them to populate the earth in a short time. 
Natural selection results from the facts that a given region is fully 
occupied by plants and animals, that these give rise to many off- 
spring, and that, owing to competition, only a small proportion 
of the offspring can grow up and in turn leave descendants. 
Owing to the large number of offspring produced, there 1s 
necessarily competition between the offspring and also between 
these and their parent. There is competition not only between 
individuals of the same species but also between different species. 
This competition is the so-called struggle for existence. In the 
case of animals it is perhaps easier to visualize than in the case 
of plants. There is, however, just as true competition between 
plants as between animals. Every farmer knows that it 1s neces- 
sary to keep down the competition between weeds and his crop 
plants by destroying the weeds. Otherwise the weeds would be 
successful and the crops would disappear. 
Survival of the fittest. In the competition between plants and 
between animals chance plays a considerable part. For example, 
many seeds never reach situations where it is possible for them 
to germinate. Nevertheless it is true that, in general, those indi- 
viduals that are best adapted to their environment and for with- 
standing competition will survive. In other words, competition 
results in the survival of the fittest. By this we do not mean the 
survival of those which are more pleasing or more useful to man- 
kind, but those which are best fitted to live under the conditions 
of their environment and to withstand competition. The survival 
of the fittest might just as well be termed “the elimination of 
the unfit,” as what really happens is that the unfit are eliminated. 
