Why did Darwin, in elucidating the driving forces of evolution, attach great importance to the indefinite (individual) variability of organisms?

Darwin considered the indefinite form of variability to be the leading material for the evolutionary process, since it is hereditary in nature and as a result of it a significant variety of individuals appears.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.