Charles Darwin was the first to purpose a feasible mechanism for evolution.
It is called natural selection.
Natural selection is the process by which populations of organisms with variations that help them survive in their environments longer, complete better, and reproduce more than those that do not have the variations.
Natural selection favors survival and reproduction.
Individuals with favorable traits are more likely to leave more offspring that is better suited for their environment.
Variations can be inherited.
The variation that increases reproductive success will have a greater chance of being passed on.
Over any generation, a population can acquire so many new traits that it becomes a new species.
An example of natural selection is a peppered moth (Biston betularia) that has light and dark phases.