Sexual selection is explained.
These questions relate to various interesting aspects of animal mating systems that result in sexual selection. Both males and females of many species can preferentially control fertilization. The mechanisms employed can occur before mating (pre-mating mechanisms) or after (post mating mechanisms).
Males typically control fertilization of a female's eggs through sperm competition mechanisms (see http://oregonstate.edu/~arnoldst/pdf_files/Jones%20et%20al_2002.pdf and http://euplotes.biology.uiowa.edu/web/sexpapers/2004/week12/choosyfemales.pdf
for further information.).
One such mechanism is called sperm precedence. In this process, males possess structures and/or behaviours that can result in preferential fertilization of a female's eggs by their own sperm, rather than that of another male, in species where females have multiple mating partners in one season. One way to bias fertilization in one's favour is to produce more sperm per ejaculate volume than other males (see http://beheco.oxfordjournals.org/cgi/content/full/10/4/358). A ...
This job addresses sexual selection.