Evolutionary Processes. Chapter 24. Populations. Group of individuals from the same species that live and breed together Smallest unit that can evolve four mechanisms can cause evolution in a population: natural selection genetic drift gene flow mutation.
Shaking just a few marbles through the narrow neck of a bottle is analogous to a drastic reduction in the size of a population after some environmental disaster. By chance, blue marbles are over-represented in the new population and gold marbles are absent.