The idea that an organism well-suited to its environment is more likely to pass on its genes forms the basis of natural selection, a core concept in Charles Darwin's theory of evolution.

Here's why:

* Survival of the Fittest: Organisms with traits better suited to their environment are more likely to survive, reproduce, and pass on those advantageous traits.

* Genetic Variation: Within a population, there's natural variation in traits. Some of these variations are more beneficial than others.

* Differential Reproduction: Organisms with more advantageous traits are more likely to reproduce successfully, leading to their genes being passed on more frequently.

Over generations, this process of natural selection leads to the evolution of species, as advantageous traits become more common and less advantageous traits become less common.