In many mammals the entire sperm enters the egg, bringing proteins that may influence development (Image: Thierry Berrod/Mona Lisa Production/SPL)
From New Scientist:
EVEN the most romantic evolutionary biologist knows that sexual reproduction is rarely a harmonious affair. Among most higher animals it is often predicated on fierce fighting, showy one-upmanship, exploitation and deception. Charles Darwin himself drew the battle lines, when he set out his ideas on sexual selection to explain the evolution of traits that provide mating advantages - either through contests between members of the same sex or by increasing attractiveness to the opposite sex. Much of what Darwin said still guides our thinking. However, since the mid-19th century it has become clear that there is more to successful reproduction than mere copulation.
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