I think a large part of it has to due with a combination and of culture and biology. Biological women are pre-wired to generally be more caring towards others since their job was to carry the baby and then in most societies they would be the most active caregiver towards the baby. Men on the other hand generally went out to hunt, and were far more exposed to competition with other men. They were also the protectors of their family or community. In the parties today, Ds are generally seen as the more compassionate party that wants to lift everyone up while the Republican Party encourages the "pull yourself up by the bootstraps" ideology of individual people reaping the benefit of their hard work.
