Darwin was fully aware of an important problem relating to his theory of natural selection. It lay in the relationship between an individual of a species and the species itself, or other individuals of the species. It is apparent in his approach to the struggle for existence in Chapter III of The Origin of Species, where he writes:

I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny.1