The structural and functional unit of the body level is the body, and the population-species unit is the population and species.
At the organismic level, such phenomena occur: reproduction, the functioning of the organism as a whole, ontogenesis, etc.
At the population-species level, the following phenomena occur: a mutation process, population waves, isolation, gene drift, natural selection.
That is, an organism, or an individual, is part of a population as part of it, as a special structural and functional component that plays an appropriate role in population-specific processes.
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.