Evolutionary conflict over the control of offspring sex ratio

There are many theories which predict how animals should control the sex ratio of their offspring. In diploids, however, such control is rarely seen. Two explanations have been suggested for this. One is that parents are simply unable to control the sex ratio of their offspring. The other is that sperm actively oppose such control. This paper examines the possibilities and consequences of parent-gamete conflict over the sex ratio. Such conflict may occur between any of the parties concerned--sperm, ova, fathers, mothers, offspring. It is concluded that gametes are indeed almost always opposed to any parental manipulation of the sex ratio. However, it is probable that the rarity of adaptive parental control of progeny sex ratio in diploids is because parents are physiologically incapable of altering the sex ratio.