What effect does natural selection have on species?

Natural selection plays a crucial role in shaping the evolution of species by enhancing the fitness of individuals that are better adapted to their environment. Fitness, in this context, refers to an organism's ability to survive, reproduce, and pass on its genes to the next generation. Individuals that possess advantageous traits—those that help them survive and reproduce in their particular ecological niche—are more likely to be selected for over time. As a result, these beneficial traits become more common in the population, leading to a gradual improvement in the overall adaptation and fitness of the species.

This process does not ensure the survival of all species, nor does it have a homogenizing effect on genetic diversity across populations—one key aspect of evolutionary dynamics is the continual fluctuations in genetic variation due to various factors, including environmental changes and genetic drift. Natural selection is not a deterministic force that guarantees fitness for all organisms, but rather a selective process that favors the individuals most suited to their current environment. Through this mechanism, natural selection drives the evolution of species, promoting adaptations that enhance survival and reproduction within specific contexts.