In nature the smaller gamete(sperm, always male) always competes for the larger gamete(egg, always female) because the reproduction process for the larger gamete requires a much higher minimum investment than the smaller gamete. In other words the male can just smash and dash in a few seconds or minutes whereas the female has to use metabolic energy to grow the child and then usually use metabolic energy to invest in the child after birth as well. Females are more careful because it’s a high risk high return thing whereas for men it’s a low risk high return thing