Here's why:

* Natural selection is the process where organisms with traits better suited to their environment are more likely to survive and reproduce.

* These successful organisms pass on their advantageous traits to their offspring.

* Over time, these beneficial traits become more common within the population, leading to evolutionary change.

Other driving forces of evolution include:

* Genetic drift: Random changes in gene frequencies within a population, especially in small populations.

* Mutation: Changes in the DNA sequence that can introduce new traits or variations.

* Gene flow: The movement of genes between populations, which can introduce new alleles and change allele frequencies.

* Sexual selection: A form of natural selection where individuals with certain traits are more likely to find mates and reproduce.

It's important to remember that:

* These forces don't act in isolation. They often interact in complex ways to shape evolution.

* Evolution is a continuous process, not a linear progression towards "better" organisms.

Let me know if you'd like me to elaborate on any of these concepts!