It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.
It is not the strongest or the most intelligent who will survive but those who can best manage change.
In the struggle for survival, the fittest win out at the expense of their rivals because they succeed in adapting themselves best to their environment.
The expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient. 2