Males Have Adapted To Battle With Competing Sperm
"In the context of sexual reproduction, natural selection is generally thought of as a pre-copulation mechanism."
Adaptation to Sperm Competition in Humans
"With the recognition, afforded by recent evolutionary science, that female infidelity was a recurrent feature of modern humans' evolutionary history has come the development of a unique area in the study of human mating: sperm competition."
RELATIONSHIPS BETWEEN SPERM LENGTH AND SPEED DIFFER AMONG THREE INTERNALLY AND THREE EXTERNALLY FERTILIZING SPECIES
"It is often assumed that longer sperm, by virtue of their increased swimming speed, have a fertilization advantage over shorter sperm when in competition to fertilize eggs."
"As was noted in the previous section, although a dominant chimpanzee may not try to monopolize time with a female in estrous, most of the competition in this species is carried out at the level of the sperm."