It should be observed, first of all, that neither of these two doctrines upholds the rights of particular groups of wage earners. They aim to bring all wage earning groups to perceive that they are part of a larger whole; they emphasize the fact that the wages of each group are what they are, more because the total wage income is what it is, than because of the special type of work performed by the group. They, however, recognize the necessity of giving extra reward for the training and skill or natural ability required for particular kinds of work, for more than common danger or disagreeableness incurred in the performance of particular kinds of work, and the like--in short, for all those factors which elevate a job above what is called common labor. As an applied doctrine, the doctrine of the unity of wage income and of the wage earners means that the same wage should be paid throughout industry for work which requires approximately the same human qualities, and which makes approximately the same demands upon the individual. The common effort involved in production is emphasized, rather than the differences between the work performed by workers in different parts of the field of production. As an applied doctrine, the doctrine of extra reward means that certain groups of wage earners should receive higher wages than other groups, because the work they perform is deemed to require considerably higher individual qualities or talents, or to make considerably greater demands upon the individuals engaged upon it.[140] The extra reward should not be regarded primarily as an ethical right; but rather as a payment to ensure the development and exercise of those higher qualities and talents required in the performance of the more skilled industrial tasks, and to ensure also the performance of the more arduous, irregular, disagreeable, and less desirable industrial tasks. It is a recognition of the fact that the spirit of serving without direct reward is not a sufficiently strong and constant motive to persuade men to make the special efforts, or to undergo the special disadvantages required for some kinds of work. It is an incentive to the development of those abilities and talents which are relatively scarce in industry; it is also an incentive to the undertaking of those tasks which the run of men, at any given time and place, regard as unusually difficult or undesirable. The extra reward for different kinds of work which are judged to require for their performance qualities equally difficult to secure, and which subject individuals to the same hardships should be the same. The test of the special reward must be in any particular case, the amount necessary to secure the performance of the work in question.