In most species females invest more so that competition is greater among males . In most species females are the sex investing most in each offspring. Therefore, a female can maximize her RS by choosing a male judiciously. DAD OR CAD 1. In birds, the egg is detached from the female earlier, so incentive to care is greater for male.
Males therefore compete among themselves for fertilization opportunities.
Investing little in each offspring, males are selected to sow their seed wherever opportunity arises. Investing considerably in each offspring, females are selected to exhibit greater selectivity in their choice of mates. One feature on which females may exercise selectivity is the male's willingness or ability to make an effective parental contribution. But wherever males do in fact invest parentally, they are under selective pressure to protect themselves against cuckoldry, and therefore males have a greater concern than females over the fidelity of their mates. Genetically-based behavior differences between males and females are inherently paradoxical, since males and females share most of the same genes.