Natural selection alters the likelihood of an organism passing on its genes to subsequent generations. The evolutionary effects of natural selection are only apparent when looking at an entire population over time. Why are the evolutionary effects of natural selection only apparent when looking at populations

Natural selection is an evolutionary process which occurs over hundreds and thousands of years. These effects are visible when we look closely at a population, because they surpass the lifetime of an individual. Moreover, the process of natural selection is involved with the evolution of a whole species, and not just a single individual.

Explanation:

Charles Darwin gave the theory of natural selection to define the process of biological evolution. This theory states that the individuals of a species with heritable traits that are superior or better suited to their environment will survive, and this process continues over time. This leads to the formation of a new species with the continued process of natural selection.

when looking for the evolutionary effects of the natural selection, one need to look over the selected population over a period of time to see the evolved inherited characters. An individual may or may not have these evolved characteristics, and hence, looking at a single individual of a species will not be a success.