Which concept relates to the survival and reproduction of the fittest within a species?

The concept that directly relates to the survival and reproduction of the fittest within a species is natural selection. This mechanism, proposed by Charles Darwin, explains how certain traits become more common in a population over time based on their advantages for survival and reproduction in a given environment. Individuals with favorable adaptations are more likely to survive and reproduce, passing those advantageous traits to the next generation.

Natural selection operates on the variation that exists within populations, leading to evolution as advantageous traits become more prevalent. Therefore, it is the process that explains how species adapt to their environments through the differential survival and reproduction of individuals. This makes it a foundational principle in evolutionary biology, highlighting the importance of environmental pressures and the resulting changes in species over time.