A unit of input can be land the firm bought, or a new machine it brought in to increase revenues. The worth or value of any additional unit which is brought in is simply determined by how much more revenue that it will bring to the firm during it's time there. In a persons case this would be the length of their employment. A firm will never pay more for an additional unit of input, whether it is a person or machine that will not increase their profits. If you found a firm that will, then rest assured they will not be around for too long!.
A great man once said that "all men are created equal". Sadly, even in this day and age, employment discrimination is still something that has to be dealt with. Employment discrimination is unequal treatment in the hiring of individuals due to race, sex or religion. To refer back to the quote, I think that man meant women as well. First I will speak on the way gender plays a role in the differences in wages in our market place. For years women could not make as much as a man and to this day still are not making as much as a man on average in the same job. Lat year female workers only made about 77% of what their male counterpart made. This pay gap between the genders is slightly more prevalent in the United States than most other countries. Some argue this is because of some religious beliefs of people place the man at the head of the house hold while women play the role of housekeeper. As David Leonhardt brought up in his article "Wage Gap Between Men and Women Shrinks", in the Book of Leviticus it is said "the value of a man's life was put at 50 shekels and a woman's at 30 shekels." Here it is obvious of our past way of thinking that women were somehow less important than men. During our day and age it has become increasingly apparent that women can play many other roles besides "housekeeper". While keeping with an economic view of this issue, it is most apparent in the increased wages of women in recent years.