After several years and multiple generations of lizards, the researchers found that both natural selection — whereby traits that enhance survival get passed down from generation to generation — and random processes contributed to the animals' genetics and their physical characteristics.

"We were actually able to see these processes and document them happening in a natural environment," Jason Kolbe, a biologist at the University of Rhode Island who led the study, told LiveScience. "We know that islands are colonized by new species over time, but we are rarely there to see it happen."

When a few individuals of a species colonize a new area, their offspring undergo what is known as the founder effect, which is a change in genetics or physical characteristics. Because of the small number of founding individuals, the new population experiences a loss in genetic variability, often resulting in individuals that are physically and genetically different from their source population.