The sentence is necessarily true. Sexual selection is a biological way one sex chooses a mate for the best reproductive success.
In The Origin of Species, Darwin put out the theory of sexual selection and elaborated on it. By presenting copious data and taking into account the idea's wide-ranging consequences, he went well beyond a straightforward explanation of the phenomena. One of Darwin's greatest assets was that he frequently wrote his literary works with a specific point in mind and gathered a tonne of data to back it up. The main goal of The Descent of Man was to demonstrate that evolutionary principles applied to humans and that we came from an ape-like common ancestor, despite the fact that Darwin's contribution to the idea of sexual selection is what gives the book its most well-known reputation.
