The contents of the book were severely backed by Darwinian evidence, which gave it its authenticity and is now considered a pioneering work in effect for the study of modern evolution theory. The survival of the fittest is a theory every person is familiar with, as it is often used as an expression in generic situations. Charles Darwin proposed a theory that contains his views on population size and the species in general. Some of the key features of this book are the building blocks of society. Some of these are as follows: each population size remains almost the same over time, species have to struggle in order to survive and individuals belonging to the same species differ significantly.