"which is the most appropriate description of evolution by natural selection? "

a population can become more adapted to its environment through natural selection. natural selection is a process by which organisms that are well adapted to their environment survives and produce more offspring. The least adapted organism die and are unable to give rise to new generation with characteristics that are not well adapted to the environment. the process is also referred to as survival for the fittest. this is the main process that brings about evolution. the theory of natural selection was fully expounded by scientist Charles Darwin.    

It explains why rocks appear in layers