Here's why:
* Definition of Gene Pool: A gene pool is the total collection of genes within a population that can be passed on to the next generation.
* Reproductive Capacity: The key aspect of a gene pool is the potential for genes to be passed on. Individuals who cannot reproduce, whether due to age, sterility, or other factors, do not contribute to the gene pool.
* Impact on Evolution: The gene pool is the foundation of evolution. Changes in the gene pool over time (through mutations, genetic drift, etc.) drive evolution. Individuals who cannot reproduce cannot contribute to these changes.
Example: Consider a population of butterflies. A butterfly that has been injured and can no longer fly might still possess genes within its body. However, because it cannot reproduce, those genes will not be passed on to offspring, and therefore are not part of the butterfly population's gene pool.
