In many species, females choose males based on their assessment of characteristics. At this level alone, the woman needs to be choosy in selecting the mate with whom she partners in creating this gene machine. So, she must be very careful about the circumstances under which she will assume this great burden. Males become good salesmen, females resistant to the sale. Males copulate with as many women as often as they can.
Females choose the partners carefully.
In general, males have low parental investment, females high. Evidence comes from different venues. Activities such as prostitution and pronography are overwhelmingly male oriented. The answer isn't simple. Natural selection transmuted all this into the emotion of love, that binds a father to his children and to their mother.