Most Helpful Guy
Before civilization, and even well in to mid 20th Century for many, women could be expected to be pregnant from the time they are mid teenagers until they die or become infertile, whichever occurs first. It is kind of hard for a pregnant woman with kids to gather enough food, hunt game, and run from lions. If she is injured, then the whole lot of them could perish. Males grew bigger and stronger than females in order to protect and provide for them and their children. This is an evolutionary advantage.
But not all males are equal. There are alpha males who have more power and resources to do that protecting and providing.
Humans utilize several mating strategies (an evolutionary advantage, since no one is best in all conditions). A common one is for females to be most attracted to alpha males who then often have several mates.
The lower caste males tend to get killed or are less capable of providing and protecting, and are therefore less desired as a mate by many females.
The underlying trait of the preferred mate is providing and protecting. Some, less evolved females, still think that means being able to run and throw things. More evolved females know that currently means money.
Most Helpful Girl
Not all of us are like that