Final answer:
The theory of evolution by natural selection explains the diversity of life as a process where organisms change over generations, with traits that offer survival and reproductive advantages being more likely to be passed on.
Step-by-step explanation:
The theory of evolution by natural selection, first proposed by Charles Darwin, explains how populations change over time and the vast diversity of life that we see on Earth today. Darwin's theory is centered around the idea that heritable characteristics which provide a survival and reproductive advantage tend to be passed on to subsequent generations. Thus, species evolve and become better suited to their environments over time.
Mutations contribute to genetic variation within a population, and these variations may improve an organism's chances of survival and reproduction. As the environment changes, different traits may become advantageous which can lead to the development of new species. This is known as adaptive evolution. Natural selection is the mechanism by which certain traits become more common in a population because they confer an advantage in survival or reproduction.
It is a common misconception that evolution explains the origin of life, but it does not. The initial appearance of life is a different field of study. However, once life began, evolution by natural selection became the driving force behind the diversity of species that followed. From the first cells to the myriad of species we see today, evolution shapes life on Earth.