Explanation:

The theory of natural selection was developed by Charles Darwin and is a fundamental principle of evolution. It explains how species change over time and how certain traits become more common in a population.

The following statement best explains the theory of natural selection:

Individuals with advantageous traits are more likely to survive and reproduce, passing on their traits to their offspring. Over time, this leads to a population with more individuals possessing the advantageous traits, as they are better suited to survive in their environment.

This means that in a given population, individuals with traits that give them an advantage in survival and reproduction are more likely to pass on those traits to their offspring. This can lead to changes in the population over time, as advantageous traits become more common and less advantageous traits become less common or disappear altogether.

In the case of the missing link between reptiles and birds, the theory of natural selection suggests that the traits that allowed the 6th specimen to survive and reproduce would have been favored by natural selection, and over time, these traits would have become more common in the population of species that gave rise to birds.