The right approach: As the question asks to explain emergence of the concept of individual differences, we should map out its genesis and the course of development. The most common error in this question is that students start emphasizing and elaborating what is individual differences.
The second part asks to signify its importance for vocational guidance. Clearly, this part requires the knowledge of actual or potential application.
The answer:The concept of individual differences is as old as is the human civilization. During prehistoric times, individuals were differentiated in terms of their hunting skills. Physical strength was the prime dimension of judgement of a king in the ancient time. The difference was attributed to the difference in the genetic makeup of the individuals.
The western world started recognising the mental strength and virtues. They started judging the difference along mental dimension on the basis of body morphology. Sheldon & Kreschmer adopted this model to differentiate personality virtues of the individuals.
Greeks were probably the earliest ones who differentiated people for their logical capacity. The father of modern psychometry , Francis Galton, too, differentiated people for their mental abilities on the basis of their physical attributes like visual acuity, sensory threshold etc. The equation however was not very valid.
In 1905, Binet and Simon developed, first known valid psychological scale to differentiate students of poor and normal mental development.
In parallel, Allport, Freud, Murray like psychologists identified individual differences along personality attributes. In psychiatric evaluation, the MMPI scale paved the way empirically valid measurement of the individual differences.
Vocational guidance and training is based on the notion that individuals have different aptitudes and attitudes . Everyone is not fit for every kind of the job. A good fit between the person and her job is imperative for performance and job satisfaction. A person profile includes physical, intellectual and personality characteristics. The vocational guidance & training in paramedical , banking and management require different profiles. Those who make career decisions based on scientific data obtained through psychometric tests are more successful and satisfied than those who make such decisions casually.( LinkedIn research ). Holland’s RIASEC model too, underscores the importance of awareness of one’s personality type to be successful and satisfied with the job one chooses.
Mentor, Arun Kumar