Natural selection
Most evolutionary biologists consider natural selection the primary process responsible for evolution. Natural selection is the process by which certain traits become more or less common in a population over time based on their effects on the survival and reproduction of the individuals that possess them.
Individuals with more advantageous traits for survival and reproduction are more likely to survive and pass on those traits to their offspring. In contrast, individuals with less advantageous traits are less likely to survive and pass on their traits.
Over many generations, this process can lead to the evolution of new species and the adaptation of existing species to their environment.